SURGICAL ANATOMY OF THE HAND AND UPPER EXTREMITY part 01

 

SURGICAL ANATOMY OF THE

HAND AND UPPER EXTREMITY

JAMES R. DOYLE, M.D.

Emeritus Professor of Surgery (Orthopaedics)

John A. Burns School of Medicine

University of Hawaii

Honolulu, Hawaii

Editor-in-Chief

The Journal of Techniques in Hand

and Upper Extremity Surgery

MICHAEL J. BOTTE, M.D.

Co-Director

Hand and Microsurgery Service

Division of Orthopaedic Surgery

Scripps Clinic

La Jolla, California

Orthopaedic Surgery Service

San Diego VA Health Care System

Clinical Professor

Department of Orthopaedic Surgery

University of California, San Diego

School of Medicine

San Diego, California

Illustrated by Elizabeth Roselius

with contributions by Christy Krames

Acquisitions Editor: Robert Hurley

Developmental Editor: Keith Donnellan

Production Editor: Thomas J. Foley

Manufacturing Manager: Benjamin Rivera

Cover Designer: Christine Jenny

Compositor: Lippincott Williams & Wilkins Desktop Division

© 2003 by LIPPINCOTT WILLIAMS & WILKINS

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Library of Congress Cataloging-in-Publication Data

Doyle, James R.

Surgical anatomy of the hand and upper extremity / James R. Doyle and Michael J. Botte.

p. ; cm.

Includes bibliographical references and index.

ISBN 0-397-51725-4

1. Hand—Anatomy. 2. Arm—Anatomy. I. Botte, Michael J. II. Title.

[DNLM: 1. Arm—anatomy & histology. 2. Hand—anatomy & histology. WE 805

D754s 2003]

QM 548 .D69 2003

611′.97—dc21

2002030007

Care has been taken to confirm the accuracy of the information presented and to describe generally

accepted practices. However, the authors and publisher are not responsible for errors or omissions or for any

consequences from application of the information in this book and make no warranty, expressed or implied,

with respect to the currency, completeness, or accuracy of the contents of the publication. Application of

this information in a particular situation remains the professional responsibility of the practitioner.

The authors and publisher have exerted every effort to ensure that drug selection and dosage set forth in

this text are in accordance with current recommendations and practice at the time of publication. However,

in view of ongoing research, changes in government regulations, and the constant flow of information

relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug

for any change in indications and dosage and for added warnings and precautions. This is particularly

important when the recommended agent is a new or infrequently employed drug.

Some drugs and medical devices presented in this publication have Food and Drug Administration

(FDA) clearance for limited use in restricted research settings. It is the responsibility of the health care

provider to ascertain the FDA status of each drug or device planned for use in their clinical practice.

10 9 8 7 6 5 4 3 2 1

To Julie Kaye Frances and Robert E. Carroll, M.D., friends and mentors.

J.R.D.

To my mother, Verona Louise Minning-Botte, M.D., and

my father, Joseph Michael Botte, M.D.

For their love, encouragement, and support

and for being the best teachers that I ever had.

M.J.B.

CONTENTS

Contributing Authors ix

Foreword by David P. Green xi

Preface xiii

SECTION I: SYSTEMS ANATOMY 1

1 Skeletal Anatomy 3

2 Muscle Anatomy 92

Appendix 2.1. Muscles of the Hand and Forearm

and Arm: Origin, Insertion, Action, and

Innervation 180

Appendix 2.2. Muscle Compartments and Fascial

Spaces of the Upper Extremity 183

Appendix 2.3. Human Forearm Muscle Difference

Index Values: A Comparison of Architectural

Features of Selected Skeletal Muscles of the Upper

Extremity 184

3 Nerve Anatomy 185

Appendix 3.1. Dermatomes of the Upper

Extremity 226

4 Vascular Systems 237

SECTION II: REGIONAL ANATOMY 295

5 Brachial Plexus 297

Vincent R. Hentz and Y. Mark Hong

6 Arm 315

7 Elbow 365

8 Forearm

Part 1: Flexor Forearm 407

Part 2: Extensor Forearm 461

9 Wrist 486

Richard A. Berger, James R. Doyle, and Michael J. Botte

10 Hand

Part 1: Palmar Hand 532

Part 2: Dorsal Hand 642

Appendix: Anatomic Signs, Syndromes, Tests, and

Eponyms 667

Subject Index 693

CONTRIBUTING AUTHORS

Richard A. Berger, M.D., Ph.D. Professor, Departments of Anatomy and Orthopaedic

Surgery, Mayo Clinic, Rochester, Minnesota

Vincent R. Hentz, M.D. Chief, Hand Division, and Professor of Functional Restoration (Hand), Department of Surgery, Stanford University School of Medicine, Palo

Alto, California

Y. Mark Hong, B.S. Department of Surgery, Stanford University School of Medicine,

Palo Alto, California

FOREWORD

The best surgeons are those well versed in anatomy. A surgeon can never learn too much anatomy, but up until now,

he or she had to go to many sources to glean a broad base of

anatomical knowledge. My own career illustrates this point.

As a medical student, I began with Gray’s massive and dry

tome, learning anatomy for the sake of anatomy, with no

clinical relevance. Then, as a resident, I discovered

Hollinshead’s three-volume text that added functional implications. I also found, at that time, Henry’s classic book with

its quaint Irish-English prose and manual mnemonics. As a

young surgeon, I sought out books that would give me quick,

snapshot glimpses of anatomy that I could memorize and

carry in my head at least until the next day in the operating

room. Grant’s Atlas was the first of these, which was later

replaced on my shelf by McMinn and Hutchings’ magnificent atlas with its lifelike-quality color plates. Specialized texts

such as Sunderland and Spinner have described wonderfully

detailed and precise anatomy, but with a limited focus.

Now the hand and upper extremity surgeon has what all

of the above resources offered and more, packed into a single volume. The thoroughness of Gray, the practical applications of Hollinshead, and the clarity of McMinn and

Hutchings have been blended into one unified source.

More than sixty crisp photographic prints depict

detailed cadaver anatomy with a precision and clarity that

rivals McMinn. Most of the drawings were created by Elizabeth Roselius, a master among contemporary medical

illustrators. The exceptionally high quality of these illustrations is complemented by a text that is not only thorough,

but also replete with clinical applications.

Another pleasant surprise in this text is the appendix of

anatomic signs, syndromes, tests, and eponyms, where even

the surgeon who has studied the history of surgery will find

new or more accurate information. Practical lessons in the

Greek and Latin derivations of words explain why similarsounding words that evolve from separate sources have different meanings.

One of the authors, James R. Doyle, was the first to

describe in detail the flexor pulley system in the fingers

(1975) and later in the thumb (1977). Jim Doyle has studied the anatomy of the hand throughout his entire professional career with the eye of an artist who can perceive

details better than most of us, with an inherent tenacity fired

even harder during a fellowship year with Robert E. Carroll,

and with an exquisite and careful attention to detail. This

book is the culmination of his life-long dedication.

Michael Botte, his co-author, brings to this project the

thoroughness and precision of a true scientist, and his input

is significant. The collaboration of Doyle and Botte has produced a remarkable piece of work that will benefit not only

the entire surgical community, but our patients as well.

Every serious hand surgeon will find a readily accessible

spot on his or her bookshelf for this text.

David P. Green, M.D.

Clinical Professor

Department of Orthopaedics

University of Texas Health

Science Center at San Antonio

San Antonio, Texas

PREFACE

Our goal has been to assemble between two covers a comprehensive collection of anatomical material designed to aid

the hand and upper extremity surgeon in the evaluation and

treatment of patients. A comprehensive knowledge of

anatomy is a major prerequisite for safe and effective

surgery. Although written by hand surgeons for hand surgeons, the authors believe that this text will also be useful to

hand therapists, anatomists, neurologists, neurosurgeons,

sports medicine surgeons and physicians, physiatrists, and

bioengineers because it is a compendium of anatomic

knowledge. The science of anatomy and the art of surgical

technique are intertwined topics that are not easily separated. Although this book is not designed as a text on operative surgery, overlap with surgical technique is inevitable,

appropriate, and complementary to the goal of the book.

Although another anatomy textbook may seem redundant, we hope the reader will agree that this text represents

a unique and current collection of material, which may not

be conveniently found elsewhere. Much of the information

can be found in other resources such as texts and journals

but we hope the reader, who like us has had difficulty recalling where we found a particular bit of information that we

now need to review or utilize in a timely fashion, will come

to value this comprehensive resource. Our primary goal in

this text is to provide a readily available source for this

information that is user friendly, easily portable, and clinically relevant.

We hope that the arrangement, clarity, and brief yet

comprehensive presentations of these topics will be of sufficient uniqueness to earn the designation of original, but we

readily admit that paraphrasing and adoption of others’

original concepts have been used (although we have done

our best to give credit where it was due). The words of Anatole France (passed on to us by Adrian Flatt) bear repetition

here, “When a thing has been said and said well, have no

scruples, take it and copy it.”

The text is divided into sections on Systems Anatomy

and Regional Anatomy, followed by an Appendix on

Anatomic Eponyms, Signs, Syndromes and Tests. The section on Regional Anatomy represents the practical component of this text because it provides the reader with

anatomic landmarks, relationships, surgical approaches,

clinical correlations, and the anatomy of selected anatomic

variations found in that region. The student of anatomy

will also recognize the immense value of the systems

approach, found in the section on Systems Anatomy, in

providing a comprehensive and overall view of a given

anatomic structure or system.

The authors take great pride in the color photographs of

fresh cadavers used in this text. A quote by Emanuel

Kaplan, about color photographs, from his foreword to

Milford’s 1968 classic monograph on Retaining Ligaments of

the Digits of the Hand seems appropriate here as well, “The

natural color illustrations add precision and eliminate the

imaginary interpretive creativity leading to error.” We hope

that the quality of our color photography can approach that

of Milford and warrant the affirmation of Kaplan on the

value of natural color photographs. We hope these color

photographs, along with the excellent illustrations, will

serve to make the anatomy in this text as realistic as possible. We also believe that the combination of these two art

forms along with the descriptive text will provide the reader

with appropriate information, which will permit accurate

preoperative evaluation, diagnosis, and effective surgical

treatment.

Anatomy, as a surgeon must deal with it, is three dimensional, but only two dimensions can be portrayed in a text.

This fact should immediately indicate to the reader that

there is no substitute for personal experience in the dissection room. In a two-dimension text, structures are often

portrayed as lying side by side when in reality they may be

vertically arrayed. A good example is the usual depiction of

the radial and ulnar arteries in the proximal forearm. The

ulnar artery is depicted as lying to the ulnar side of the

radial artery in the same anatomic plane whereas, in reality,

the ulnar artery is deep and ulnar to the radial artery and is

often difficult to find. The reader should also note that the

anatomic variations included are those that the authors perceive to have some practical clinical relevance to the region

and that the list of variations is not encyclopedic.

Reported differences in anatomy may be due to

anatomic variations as well as inter-observer variability and

subsequent interpretation of the observation. It would seem

reasonable to assume that all observers of a particular region

or segment of anatomy would see or observe the same

things and interpret what they saw in a similar uniform

fashion. Such is not the case, and although many points of

anatomy are agreed upon there are many that are not. Two

illustrative examples come readily to mind: (1) the arcade of

Struthers’ in the arm and (2) the location of the sesamoid

bones about the MP joint of the thumb. Some authors

describe in detail the arcade of Struthers’ 8 cm above the

medial humeral epicondyle and attach clinical significance

to it as a potential site of ulnar nerve compression in the

arm. Others claim that it does not exist or at least that they

have never seen it and thus it has no clinical relevance. The

location of the ulnar and radial sesamoid bones about the

MP joint of the thumb have been reported to be in the

adductor pollicis and flexor pollicis brevis tendons respectively or in the palmar plate where they possess articular cartilage and articulate with the thumb metacarpal; two

entirely different pictures of the same structures. Interobserver variability may be illustrated by the imperfect, yet

humorous, analogy of six blind persons examining a camel.

Each of their descriptions are based upon their particular

location about the camel. Their significant inter-observer

variation results in a series of descriptions that would confound even a camel veterinarian. The authors include themselves in those observers who may be subject to imperfect

observation as well as faulty interpretation. Thus, there may

be a lively correspondence and commentary generated by

this text.

We believe that studies that have large numbers of specimens in their data base have a greater potential for reflecting what might be considered more common and thus

likely to be encountered in the day to day practice of

surgery. Studies with small numbers of specimens in which

several patterns or categories of anatomical arrangement are

noted tell us that significant variation exists. It may not tell

us the true incidence of a given pattern or arrangement in

spite of the authors’ conscientious reporting of one, two, or

three cases in their series which demonstrated a particular

pattern or arrangement. Such studies though, are still

important and tell us that significant variation exists in that

particular structure or region and that the surgeon must be

prepared to encounter such an arrangement or even a new

and unreported pattern or arrangement.

By now, the reader has begun to appreciate the fact that

anatomy is not a “fixed” science, but rather an evolving or

developing endeavor with many remaining challenges and

opportunities.

All authors have their own methods for placing thoughts

on paper. This quote from Wallace Stegner1, although

directed at the writer of autobiography or fiction, seems

appropriate, “You take something that is important to you,

something you have brooded about. You try to see it as

clearly as you can, and to fix it in a transferable equivalent.

All you want in the finished print is the clean statement of

the lens, which is yourself, on the subject that has been

absorbing your attention.”

The authors wish to recognize their debt to those surgeons and anatomists who have studied and described their

anatomic findings in the upper extremity and to our many

mentors and colleagues who have taught, encouraged, and

inspired us.

Finally, the authors wish to acknowledge their debt to

Robert Hurley and Keith Donnellan of the editorial staff at

Lippincott Williams & Wilkins who have patiently guided

and encouraged us throughout this process in such a competent and professional manner. We also owe a great debt to

Elizabeth Roselius, medical artist, for her understanding of

complex anatomic concepts and her ability to convert those

concepts into clear and concise drawings.

James R. Doyle, M.D.

Michael J. Botte, M.D.

1 Stegner WE, Where the bluebird sings to the lemonade springs. New

York: Random House, 1992.

xiv Preface

SECTION

I

SYSTEMS ANATOMY

I

1

SKELETAL ANATOMY

MICHAEL J. BOTTE

The skeletal anatomy of the upper limb is divided into the

shoulder girdle, the arm, elbow, forearm, carpus, and

hand. The scapula, clavicle, and sternum comprise the

skeletal shoulder girdle. The mid-portion of the humerus

comprises the skeletal arm. The distal humerus and proximal ulna and radius form the skeletal elbow. The radius

and ulna and associated soft tissues comprise the skeletal

forearm. The carpus consists of the distal radius and ulna

along with the eight carpal bones: the scaphoid, lunate,

capitate, trapezium, trapezoid, triquetrum, hamate, and

pisiform. The hand contains 19 bones: 5 metacarpals, 5

proximal phalanges, 4 middle phalanges, and 5 distal phalanges.

The skeleton of the upper limb is attached relatively

loosely to the trunk. The clavicle provides the only direct

skeletal connection of the upper limb to the axial skeleton,

articulating through the sternoclavicular joint. The upper

limb is substantially stabilized to the thorax by muscles of

the soft tissue scapulothoracic articulation. This relatively

loose attachment maximizes upper limb mobility and flexibility, allowing rotation and translation of the scapula on

the thorax. The loose connection of the upper limb to the

trunk is in contrast to the lower extremity, where the majority of the stabilization is through the skeletal connection of

the hip joint.

In the following sections, each bone and associated

joint of the upper limb is discussed. The ossification centers, descriptive osteology, articulations, muscle attachments, and clinical implications are discussed. Osseous

anomalies or variations, when significant, are described as

well.

CLAVICLE

Derivation and Terminology

The clavicle derives its name from the Latin clavis, meaning

“key” (1–3). The plural of clavicle is claviculae (1,3). The

clavicle has been referred to alternatively as the clavicula.

Clavicular indicates “relating to the clavicle” (1,3).

Ossification Centers

The clavicle begins to ossify earlier than any other part of

the skeleton (4,5). It has three ossification centers, two primary centers for the shaft and one secondary center for the

medial end (Fig. 1.1). The primary centers for the shaft

consist of a medial and a lateral center, both of which

appear during the fifth or sixth week of fetal life. The centers fuse to each other approximately 1 week later. The secondary ossification center is located at the sternal end of the

clavicle and first appears approximately the eighteenth or

twentieth year, usually about 2 years earlier in women. The

secondary center unites with the remaining portion of the

clavicle at approximately the twenty-fifth year. An acromial

secondary center sometimes develops at 18 to 20 years of

age, but it usually is small and fuses rapidly with the shaft

(2,6).

The clavicle does not ossify in quite the normal manner

of endochondral ossification, as occurs in most of the skeleton. Although the medial and lateral ends of the clavicle do

undergo endochondral ossification, the mid-portion is

formed by a process that shares features of both endochondral and intramembranous ossification. The clavicle is preformed of cartilage in embryonic life, but does not proceed

with endochondral ossification in the conventional manner.

Instead, the cartilage model simply serves as a surface for the

deposition of bone by connective tissues. Eventually, the cartilage is resorbed and the clavicle becomes fully ossified

(7–10). [The process is shared by the mandible. The remaining long bones of the upper extremity are formed by conventional endochondral ossification (7).]

Osteology of the Clavicle

The clavicle is a curved, roughly “S”-shaped long bone that

lies subcutaneously along the anterolateral base of the neck.

When viewed from its superior side, the clavicle shape

resembles the letter “F,” with the concavity of the medial

curve being directed posteriorly, and the concavity of the

lateral portion directed anteriorly (Figs. 1.2 and 1.3). It

forms the most anterior portion of the shoulder girdle, and

is subcutaneous along its entire course. It is directed nearly

horizontally toward the acromion of the scapula, located

immediately superior to the first rib.

The clavicle consists of cancellous bone surrounded by

cortical bone (see Figs. 1.2 and 1.3). The cortical bone is

thicker in the intermediate or shaft portion, and relatively

thin at the acromial and sternal ends. The clavicle is unique

in that, unlike most other long bones, it usually has no

medullary cavity (5). This is related to its unique form of

ossification, which consists of both endochondral and

intramembranous ossification.

The clavicle has specific differences in men and women

and can be used to determine sex of a skeleton or specimen.

The clavicle in general is shorter, thinner, less curved, and

smoother in women than in men. Midshaft circumference

of the clavicle is a reliable single indicator of sex, especially

combined with the bone weight and length (11,12). In persons who perform heavy manual labor, the clavicle becomes

thicker and more curved, and its ridges become more distinct for muscular attachment.

For its descriptive osteology, the clavicle is discussed here

from lateral to medial, beginning with the acromial portion

and moving to the lateral one-third, medial two-thirds, and

the sternal portion.

Acromial Portion of the Clavicle

The most laterally positioned part of the clavicle the acromial portion, which contains the articulation for the

acromion of the scapula and the associated attachments

of the acromial clavicular ligaments. The acromial portion of the clavicle is somewhat flattened and is wider

compared with the mid-portions. The superior surface is

flat, with a rough ridge along the posterosuperior portion. The anterior surface of the acromial portion is concave and smooth, the posterior surface convex and

smooth, and the inferior somewhat convex and rough.

On the inferior surface, there are multiple small foramina

for nutrient vessels. The articular surface is oval and

directed obliquely and inferiorly. The rim of the articular

margin is rough, especially superiorly, for attachment of

the thick acromioclavicular ligaments. The acromial portion of the clavicle projects slightly superiorly to the

acromion of the scapula. The acromioclavicular joint is

palpable approximately 3 cm medial to the lateral border

of the acromion.

Lateral Third of the Clavicle

The lateral third of the clavicle is wider and flatter than the

more medial portion. This portion has distinct superior,

inferior, anterior, and posterior surfaces. The superior and

inferior surfaces are flat. The posterior surface is rounded,

convex, and slightly thickened. The anterior surface is

mildly concave, and becomes wider and rough in the most

lateral portion as it approaches the acromion. The posterior

and anterior portions have roughened areas for the attachment of the trapezius and deltoid muscles, respectively. On

its inferior surface in the lateral third, there is the conoid

4 Systems Anatomy

FIGURE 1.1. Illustration of right clavicle showing the three centers of ossification. There are

two primary centers (medial and lateral) for the

shaft and one secondary center for the medial

end.

FIGURE 1.2. Right clavicle, superior surface, showing muscle origins (red) and insertions (blue).

tubercle for attachment of the conoid ligament (the medial

portion of the coracoclavicular ligament). Lateral to the

conoid tubercle is the trapezoid line, an oblique line on the

undersurface for attachment of the trapezoid ligament

(which is the lateral portion of the coracoclavicular ligament).

Medial Two-Thirds of the Clavicle

The medial two-thirds of the clavicle is more rounded than

the sternal end or the lateral thirds, and becomes slightly

wider from lateral to medial. Anteriorly, the surface is

straight or curved with a mild convexity. Along this anterior

surface is the large origin of the clavicular head of the pectoralis major.

The posterior border of the clavicle in the medial twothirds is smooth and concave, and oriented toward the base

of the neck. The posterior border widens as it approaches the

sternum. Posteriorly and inferiorly, there is the small attachment area for the origin of the sternohyoid muscle, which

extends into the sternal region. Also along the posterior border, on the superior margin, is the area of origin of the sternocleidomastoid muscle. On the posterior border of the inferior surface of the lateral two-thirds is a rough tubercle, the

conoid tubercle, for attachment of the conoid ligament.

From the conoid tubercle to the costal tuberosity (see later),

there is a large attachment area for the insertion of the subclavius muscle. This surface also gives attachment to a layer

of cervical fascia, which envelops the omohyoid muscle.

In the medial portion of the medial two-thirds, the clavicle becomes slightly wider and thicker, especially when

viewed from above or below. In this medial portion, the

clavicle is rougher both anteriorly and posteriorly. On the

inferior surface of the medial clavicle extending into the

sternal portion is a delineated long roughened area, the

costal tuberosity, which is approximately 2 cm in length.

The costoclavicular ligament attaches in this area. The rest

of the area is occupied by a groove, which gives attachment

to the subclavius muscle. The clavipectoral fascia, which

splits to enclose the subclavius muscle, is attached to the

margins of the groove.

The brachial plexus is located deep to the mid-portion of

the clavicle. The mid-portion of the clavicle is formed by

the intersection of two curves of the bone, anteriorly convex on the lateral portion, and anteriorly concave in the

medial portion. At the junction of these two curves, the

clavicle overlies the divisions of the brachial plexus and the

subclavian vessels.

Sternal Portion of the Clavicle

At the sternal end, the clavicle becomes wider at the midportion, but not in general as wide as the acromial end. The

relative widths of the bone can be used for easy determination between the sternal and acromial ends. As the sternal

end flares out, it becomes rough and more irregular. The

sternal end usually is easily palpable.

The sternal portion contains a sternal articular surface

for the manubrium of the sternum. The sternoclavicular

joint contains the articular disc. There is a triangular surface

for articulation with the cartilage of the first rib in this area

on the inferior surface of the clavicle. Surrounding the articular surfaces is a rim that is roughened for the attachments

of the sternoclavicular and costoclavicular ligaments. The

sternal end of the clavicle lies slightly above the level of the

manubrium and hence usually is palpable. This area is covered by the sternal end of the sternocleidomastoid muscle.

On the inferior surface of the sternal portion there is a

rough, raised ridge, the costal tuberosity, which extends into

the medial third of the clavicle (see earlier). The costoclavicular ligament attaches to the costal tuberosity.

Associated Joints

The clavicle articulates with the acromion of the scapula laterally (acromioclavicular joint), and with the manubrium of

the sternum and cartilage of the first rib medially (sternoclavicular joint; Fig. 1.4).

1 Skeletal Anatomy 5

FIGURE 1.3. Right clavicle, inferior surface, showing muscle origins (red) and insertions (blue).

The acromioclavicular joint between the lateral end of

the clavicle and the acromion of the scapula is stabilized by

several structures: the acromioclavicular ligaments, coracoclavicular ligament, and joint capsule.

The acromioclavicular ligament crosses the acromioclavicular joint, most developed on the superior portion of the

joint. The ligament is oriented along the axis of the clavicle.

It attaches to the roughened areas on the adjacent ends of

the clavicle and acromion.

The coracoclavicular ligament stabilizes the acromioclavicular joint by anchoring the clavicle to the coracoid of the

scapula. It is more efficient in stabilizing the acromioclavicular joint than the acromioclavicular ligaments, even

though it does not cross the joint. It consists of two parts:

the trapezoid ligament (located laterally) and the conoid ligament (located medially).

The trapezoid ligament, as its name implies, is quadrangular or trapezoid in shape. It is broad and thin, and crosses

from the upper coracoid surface to the trapezoid line on the

inferior surface of the clavicle. It follows an oblique or

almost horizontal direction, ascending laterally as it crosses

from the coracoid process to the clavicle above.

The conoid ligament, located medial and slightly posterior to the trapezoid ligament, attaches from the root of the

coracoid process in front of the scapular notch, and ascends

superiorly to attach to the conoid tubercle of the undersurface of the lateral clavicle. It is a dense ligament, roughly triangular in shape.

At the sternal articulation, the sternoclavicular joint is

located at the superior portion of the manubrium. The

first costal cartilage is located inferior to the sternoclavicular joint. The inferior surface of the medial end of the

clavicle articulates with a small portion of the first costal

cartilage.

The sternoclavicular articulation involves the medial end

of the clavicle, which articulates with both the sternum (at

the sternoclavicular or clavicular notch) as well at the adjacent superior surface of the first costal cartilage. An articular disc composed of fibrocartilage lies between the end of

the clavicle and the sternum. The medial end of the clavicle

is convex vertically but slightly concave anteroposteriorly,

and therefore the shape often is described as “sellar” (pertaining to a saddle, saddle-shaped) (1,3).

The articular disc of the sternoclavicular joint is flat and

generally circular, attached superiorly to the superoposterior

border of the clavicular articular surface (see Fig. 1.4.). The

disc is centrally interposed between the articulating surfaces

of the clavicle and sternum, and divides the joint into two

cavities, each of which is lined with synovial membrane.

The articular disc is thicker peripherally and in the superoposterior portion. The disc is attached inferiorly to the first

costal cartilage near its sternal junction. In the remaining

portion of the disc’s circumference, it is attached to the joint

capsule of the sternoclavicular joint. Most of the motion at

the sternoclavicular joint occurs between the articular disc

and the clavicle, with less movement occurring between the

articular disc and the sternum (5).

The ligaments and soft tissues that stabilize the sternoclavicular joint include the joint capsule, the anterior sternoclavicular ligament, the posterior sternoclavicular ligament, the interclavicular ligament, and the costoclavicular

ligament (4,5) (see Fig. 1.4).

The joint capsule lies deep to the ligaments, and completely surrounds the articulation. The stability of the joint

is shared by the joint capsule and the associated ligaments.

The joint capsule varies in thickness and strength. The anterior and posterior portions usually are thicker and stronger,

reinforced by the anterior and posterior sternoclavicular lig6 Systems Anatomy

FIGURE 1.4. Superior portion of anterior manubrium showing medial clavicles and sternoclavicular joints.

aments. The joint capsule is reinforced by the interclavicular ligament superiorly. The inferior portion of the sternoclavicular joint capsule is thin, and resembles areolar tissue

(4).

The anterior sternoclavicular ligament is broad and covers the anterior portion of the sternoclavicular joint (see Fig.

1.4). It is attached superiorly to the upper and anterior portion of the medial end of the clavicle. The ligament passes

obliquely downward and medial from the clavicle to the

sternum. The ligament attaches to the superior part of the

manubrium. The sternocleidomastoid muscle passes over

the anterior sternoclavicular ligament. The joint capsule

and articular disc lie posterior to the anterior sternoclavicular ligament.

The posterior sternoclavicular ligament also is broad,

similar to the anterior sternoclavicular ligament. The ligament spans the posterior portion of the sternoclavicular

joint, attached to the superior portion of the medial end of

the clavicle. It passes obliquely inferiorly and medially (similar to the anterior sternoclavicular ligament), to attach inferiorly to the dorsal portion of the superior manubrium. The

articular disc and synovial membranes of the sternoclavicular joint lie anteriorly. The sternohyoid and the sternothyroid muscles lie posteriorly.

The interclavicular ligament connects the medial ends

of the two clavicles and is attached to the superior border of

the manubrium. The ligament spans from one clavicle

to the other, stretching along the superior border of the

manubrium. It is of variable size between individuals and

forms the floor of the jugular notch (see Fig. 1.4). Anterior

to the interclavicular ligament is the sternocleidomastoid

muscle. Dorsal to the ligament are the sternohyoids. The

interclavicular ligament adds considerable strength to the

superior portion of the sternoclavicular joint capsule.

The costoclavicular ligament is located at the inferior border of the medial end of the clavicle, outside of and just lateral

to the joint capsule (see Fig. 1.4). It helps stabilize the medial

end of the clavicle to the superior portion of the medial part

of the cartilage of the first rib. The ligament has an oblique

orientation, extending medially and inferiorly from the inferomedial clavicle to reach the superior portion of the costal cartilage. The clavicle has a slight ridge on its inferomedial end,

the costal tuberosity, to which the costoclavicular ligament

attaches. Anterior to the costoclavicular ligament lies the tendon of the origin of the subclavius muscle. 

Posterior to the

costoclavicular ligament is the subclavian vein.

Muscle Origins and Insertions

Muscle attachments to the clavicle include the trapezius,

pectoralis major, deltoid, sternocleidomastoid, subclavius,

and sternohyoid (see Figs. 1.2 and 1.3). The trapezius

inserts onto the superolateral shaft. The clavicular head of

the pectoralis major originates from the anteromedial portion of the shaft. The deltoid originates from the anterolateral portion of the shaft. The sternocleidomastoid muscle

originates from the superomedial portion of the shaft. The

subclavius inserts onto the inferior surface of the middle

third of the shaft. The sternohyoid originates from the

inferomedial surface (2,4,5).

Clinical Correlations: Clavicle

Relationship to the Brachial Plexus

The mid-portion of the clavicle lies approximately over the

divisions of the brachial plexus. The clavicle is an important

bony landmark in planning incisions for supraclavicular or

infraclavicular brachial plexus exploration. It is a useful

landmark in the orientation and identification of structures

in brachial plexus. Although rare, neurovascular compression of the brachial plexus can occur with clavicular fractures (13).

Clavicle Shaft Fractures

The clavicle is one of the most commonly fractured bones

(14). Fractures most often occur at the junction of the lateral one-third and medial two-thirds, its weakest portion

(5,15,15a). The distal portion usually is displaced inferiorly,

in part because of the weight of the shoulder. The proximal

portion is displaced little. Nonunion is rare, but usually

occurs in the middle third (16). The clavicle commonly is

injured because of its subcutaneous location.

Neer Classification of Distal Clavicle Fractures

n Type 1: A nondisplaced, nonarticular fracture of the distal clavicle, with the acromioclavicular joint and ligaments intact.

n Type 2: A displaced fracture of the distal clavicle that is

interligamentous (fracture extends between the conoid

ligament medially and trapezoid ligament laterally). The

conoid ligament is torn, the trapezoid ligament remains

attached to the distal segment, and the medial segment is

displaced superiorly (due to loss of the conoid ligament).

The distal fragment remains aligned to the acromioclavicular joint (due to stabilization of intact trapezoid ligament).

n Type 3: An intraarticular fracture of the distal clavicle

that is lateral to the coracoclavicular ligaments. There is

no displacement because the ligaments are intact

(17–19).

Acromioclavicular Separation

Injury at the acromioclavicular joint (AC separation) has

been classified by several descriptions. One of the most

1 Skeletal Anatomy 7

widely used classifications divides the injury into three

types. Type I is a partial tear of the ligaments, involves no

joint subluxation, and usually is treated symptomatically.

There is minimal widening (if any) of the acromioclavicular joint space, which normally measures 0.3 to 0.8 cm.

Type II involves a more extensive but incomplete tear,

with partial subluxation seen radiographically. Widening

of the acromioclavicular joint or bone surfaces can be 1 to

1.5 cm. There usually is an associated increase in the coracoclavicular distance by 25% to 50%. Treatment also is

symptomatic, often with shoulder support with an immobilizing device. Type III is a complete disruption of the

ligaments with dislocation of the clavicle from the

acromion. There is marked widening of the acromioclavicular joint, usually greater than 1.5 cm. It often is treated

surgically with internal fixation and repair or reconstruction of the ligaments (17). Recently, these injuries have

been classified into six types (20–22). Types I, II, and III

are similar to the traditional classification system. A type

IV injury is rare, and involves posterior dislocation of the

distal end of the clavicle. The clavicle is displaced into or

through the trapezius muscle. Shoulder motion therefore

usually is more painful than with the type III injury. The

type V injury is an exaggeration of type III in which the

distal end of the clavicle appears to be grossly displaced

superiorly toward the base of the neck. The apparent

upward displacement is the result of the downward displacement of the upper extremity. There is more extensive

stripping of soft tissues of the clavicle and the patient usually has more pain than in the type III injury. The type VI

injury involves a subcoracoid dislocation of the distal clavicle. There is an inferior dislocation of the distal clavicle

(inferior to the coracoid process) and posterior to the

biceps and coracobrachialis tendons. Because of the

amount of trauma required to produce a subcoracoid dislocation of the clavicle, there may be associated fractures

of the clavicle and upper ribs or injury to the upper roots

of the brachial plexus. Management of types IV, V, and VI

usually involves operative repair/reconstruction (20–22).

Type III injuries have been further divided into additional

variants, including those in children and adolescents

involving a Salter type I or II fracture through the physis

of the distal clavicle, or a complete separation of the

acromioclavicular articular surfaces combined with a fracture of the coracoid process (22).

Sternoclavicular Separation

Sternoclavicular separation is rare compared with AC separation. Posterior dislocations may cause pressure on the

great vessels or airway located posterior to the joint. Computed axial tomography is helpful in determining the direction of subluxation/dislocation. Reduction of the posterior

dislocation is safest in the operating room in the presence of

a general or thoracic surgeon if damage has occurred or is

discovered involving the vessels or airway.

Posttraumatic Osteolysis of the Distal Clavicle

After injury to the shoulder, such as a type I injury to the

acromioclavicular joint, resorption of the distal end of the

clavicle occasionally may occur. The osteolytic process,

which is associated with mild to moderate pain, usually

begins within 2 months after the injury. Initial radiographs

show soft tissue swelling and periarticular osteoporosis. In

its late stage, resorption of the distal end of the clavicle

results in marked widening of the acromioclavicular joint

(17).

Cleidocranial Dysostosis

Cleidocranial dysostosis is a partial or complete absence of

the clavicle. It is associated with abnormal ossification of

the skull bones (23). Patients with congenital absence of the

clavicle have shown little or no limb dysfunction; however,

after clavicular excision (for trauma or tumor), noted findings have included weakness, drooping of the shoulder, and

loss of motion (15,19,24).

Clavicular Dysostosis

Clavicular dysostosis is a result of incomplete union of the

two ossification centers of the clavicle (23).

SCAPULA

Derivation and Terminology

The scapula derives its name from the Greek for “spade”

(1,3). The plural of scapula is scapulae (1). Graves’ scapula

indicates a scapula in which the vertebral border is concave.

Scaphoid scapula indicates a scapula in which the vertebral

border is concave (same as Graves’ scapula). Winged scapula

indicates a scapula that is positioned with the vertebral border prominent (1).

Ossification Centers and Accessory Bones

The scapula has seven to eight ossification centers: one for

the body, two for the coracoid process, two for the

acromion, one for the medial (vertebral) border, and one for

the inferior angle (Fig. 1.5). Additional centers may be present to help form the inferior and superior portions of the

glenoid cavity (4,5).

The body begins to ossify at approximately the second

month of fetal life, forming an irregular quadrilateral plate

of bone near the scapular neck, adjacent to the glenoid cavity. The plate extends to form the major part of the scapula.

8 Systems Anatomy

The spine extends up from the dorsal surface of this plate

approximately the third month of fetal life. At birth, the

major part of the scapula is osseous. The glenoid cavity,

coracoid process, the acromion, and the vertebral border

and inferior angle remain cartilaginous at birth. An ossification center appears in the middle of the coracoid process

during the first year after birth. This ossification center

joins the rest of the scapula at approximately the fifteenth

year. Between the fourteenth and twentieth years, ossification of the remaining parts of the scapula takes place in

quick succession. Ossification of these parts occurs in the

following order: the base of the coracoid process, the base of

the acromion, the ossification centers in the inferior angle

and adjacent part of the medial border, the tip or lateral

portion of the acromion, and the remainder of the medial

border (2,4,5).

The base of the acromion is formed from three or four

ossification centers. It is partially formed by an extension

from the spine of the scapula (from the ossification center

of the body), and partially from the two centers of the

acromion (which previously have united to each other). The

tip of the coracoid process may develop a separate ossification center. These various centers join the body by the

twenty-fifth year. Persistence of an ossification center of the

acromion that does not fuse with the others or with the

scapula can present as an accessory bone, the os acromiale.

An os acromiale usually is located at the lateral margin of

the acromion, is of variable size and shape, and usually is

bilateral (25). It also is possible for the os acromiale to exist

as a small accessory ossicle directly above the greater

tuberosity of the humerus. This ossicle is separated from the

acromion by approximately 1 cm, and usually is somewhat

circular in shape.

The superior third of the glenoid cavity may be ossified

from a separate center, or may ossify from an extension of

the center at the base of the coracoid. When ossification is

from a separate center, the center usually ossifies between

the tenth and eleventh years. This superior portion of the

glenoid then joins the rest of the scapula between the sixteenth and eighteenth years. An epiphyseal plate or crescentic epiphysis also may appear for the lower part of the glenoid cavity, which is thicker peripherally. This rim converts

the flat cavity into the gently concave fossa that is present in

the adult glenoid (2,4,5).

1 Skeletal Anatomy 9

FIGURE 1.5. Illustration of right scapula showing several centers of ossification. The scapula may have

seven to eight (or more) ossification centers: one for

the body, two for the coracoid process, two for the

acromion, one for the medial (vertebral) border, and

one for the inferior angle. Additional centers may be

present to help form the inferior and superior portions of the glenoid cavity.

Osteology of the Scapula

The scapula is a large, flat, triangular bone that spans the

dorsal aspect of the second through seventh ribs (Figs. 1.6

to 1.8). Its synovial articulations include those with the

humerus and the clavicle. In addition, the scapula is stabilized to the dorsal surface of the thorax by muscle, forming

the scapulothoracic articulation.

The main processes (acromion, coracoid, and subchondral portions of the glenoid) as well as the thicker portions

of the body contain trabecular bone (see Figs. 1.6 to 1.8).

The remaining portions generally consist of thin cortical

bone. The central portions of the supraspinous fossa and

most of the infraspinous fossa consist of thin cortical bone.

Occasionally the bone is so thin that it may appear translucent or may have areas that are incompletely ossified, being

filled with connective tissue.

Osteology measurements are given in Figure 1.9 and

Table 1.1. The mean length of the scapulae from the superior angle to the inferior angle is 15.5 cm. The width of the

scapula from the medial border to either the superior or

inferior rim of the glenoid is approximately 10.6 cm. The

scapula is significantly larger in men than women (26)

(Table 1.1).

For descriptive osteology, the scapula has two surfaces,

the costal (anterior) and the dorsal (posterior). It contains

the process of the acromion, the coracoid, and the spine. It

has three borders: superior, medial (or vertebral), and lateral

(or axillary). It has three angles: inferior, superior, and lateral (26,27).

10 Systems Anatomy

FIGURE 1.6. Right scapula, anterior surface, showing muscle origins (red) and insertions (blue).

Surfaces of the Scapula

The costal surface forms the large subscapular fossa, a

slightly concave surface for the origin of the subscapularis

(see Fig. 1.6). The medial two-thirds of the subscapular

fossa is roughened, with ridges that course laterally and

superiorly. These ridges give origin to tendinous attachments of the subscapularis. Along the medial border of the

costal surface is a long, thin rim that provides the insertion

of the serratus anterior.

The dorsal surface is slightly convex from superior to

inferior. It contains the two fossae for the supraspinatus and

infraspinatus, separated by the prominent spine of the

scapula. The supraspinatus fossa, which is much smaller

than the infraspinatus, is smooth, concave, and broader at

its medial aspect than its lateral border. It is bordered by the

spine inferiorly, the coracoid process laterally, and the superior and medial rim of the scapula superiorly and medially,

respectively. The supraspinatus muscle originates from the

medial two-thirds of the fossa (see Fig. 1.7).

The infraspinatus fossa is approximately three times

larger than the supraspinatus fossa. It has a slight concavity

superiorly to inferiorly, especially along the medial border.

There is a slight convexity throughout its central portion,

and a deep groove near the axillary border. The attachments

of the infraspinatus are located on the lateral third of the

fossa (see Fig. 1.7).

There is a slight bony ridge that runs along the lateral

border of the dorsal surface of the scapula. The ridge runs

from the lower part of the glenoid cavity, downward and

backward to the medial border, to an area approximately 2

to 3 cm superior to the tip of the inferior angle. This ridge

serves for the attachment of a fibrous septum that separates

the infraspinatus from the teres major and teres minor. The

surface between the ridge and the lateral border is narrow in

the superior two-thirds. In this area, the ridge is crossed

near its center by a groove that contains the circumflex

scapular vessels. This ridge provides attachment for the teres

minor superiorly and for the teres major inferiorly. The area

of origin of the teres major is broader and somewhat triangular. The latissimus dorsi muscle glides over the lower

region, and frequently a few muscle fibers arise at the inferior angle of the scapula. The teres muscles are separated

from each other by a fibrous septum that extends along an

1 Skeletal Anatomy 11

FIGURE 1.7. Right scapula, posterior surface, showing muscle origins (red) and

insertions (blue).

oblique line from the lateral border of the scapula to an elevated ridge (2,4,5).

Processes of the Scapula

The scapula has three main processes: the acromion, the

coracoid process, and the spine of the scapula (see Figs. 1.6

to 1.9).

The acromion is a lateral extension of the spine. The

process becomes flattened as it extends laterally, overhanging the glenoid, and forms the most superior portion or

“summit” of the scapula (see Fig. 1.9A–E). The shape is

variable, with a flat configuration in 23%, curved in 63%,

and hook-shaped in 14% (26). The mean length of the

acromion in the anteroposterior plane is 4.8 cm. The mean

width of the acromion in the mediolateral plane is 2.19 cm,

and the mean thickness is 9.4 mm. The narrowest portion

forms a neck, the diameter of which is 1.35 cm (26) (Table

1.1). The acromion is located an average distance of 16 mm

from the glenoid (26). The superior surface is rough and

convex and provides attachment for the thick acromioclavicular ligaments and a portion of the deltoid muscle. The

remaining portions are subcutaneous and smooth. The

inferior surface of the acromion is smooth and concave. The

lateral border is thick and irregular and usually has three or

four tubercles for the tendinous origins of the deltoid muscle. The medial border is shorter than the lateral and concave. In this area, the acromion provides a portion of the

attachment of the trapezius muscle. On this medial border,

there is a small oval area of articular cartilage for articulation

with the acromial end of the clavicle. The apex of the

acromion is a small area where the medial and lateral borders intersect. In this area, the coracoacromial ligaments

form their attachment. Inferiorly, where the lateral border

of the acromion becomes continuous with the lower border

of the crest of the spine, the acromial angle is located. The

acromial angle can be palpated subcutaneously and used as

a landmark.

The coracoid process is a thick, curved projection of

bone that projects anteriorly, superiorly, and medially from

12 Systems Anatomy

FIGURE 1.8. Right scapula, lateral view,

showing glenoid cavity and profile of coracoid process, acromion, and body.

FIGURE 1.9. A: Anterior view of the right scapula showing the standard terminology of the

anatomic regions. B: Posterior view of the right scapula showing terminology and general measurements. The measurements include [1] the maximum length of the scapula; [2] the width of the

scapula measured to the posterior rim of the glenoid; [3] the width of the scapula measured to the

anterior rim of the glenoid (also shown in Fig. 1-9C); [4] the inferior scapular angle; [5] the anteroposterior thickness of the medial border of the scapula measured halfway along the medial edge

of the scapula and 1 cm from the edge; and [6] the distance from the superior rim of the glenoid

to the base of the suprascapular notch. The measurement values are shown in Table 1.1. C: The

right scapula (superior view as shown in the inset) showing the measurement of the spine. The

measurements include [7] the length of the scapular spine measured from the medial edge of the

scapula where it meets with the scapular spine to the lateral edge of the acromion; [8] the distance

from the medial edge of the scapula where it meets with the scapular spine to the edge of the spinoglenoid notch; [9] the anteroposterior width of the spine measured 1 cm from the medial edge

of the scapula; [10] the anteroposterior width of the spine measured 4 cm from the medial edge

of the scapula; [11] the anteroposterior width of the spine at the lateral edge (spinoglenoid notch);

and [12] the anteroposterior thickness of the acromial neck at its thinnest diameter. Also shown is

measurement [3], which is the width of the scapula measured on the anterior surface. The measurement values are shown in Table 1.1. D: Scapular measurements of the length [13], width [14],

and thickness [15] of the acromion, and the coracoacromial distance [16], as seen from the superior

view of the right scapula. The measurement values are shown in Table 1.1.

(continued on next page)

A B

C D

14 Systems Anatomy

FIGURE 1.9. (continued) E: Lateral view of the right scapula, showing the

coracoacromial distance [16], the minimal distance between coracoid and

acromion [17], and the dimensions of the glenoid fossa [18–20]. The measurement values are shown in Table 1.1. F: Measurements of the thickness of the

scapular head [21,22] and glenoid tilt angle [23] as seen from the inferior view

of the right scapula. The measurement values are shown in Table 1.1. G: Dimensions of the coracoid process of the right scapula as seen from the anterior

view. Measurements include the length of the coracoid from the tip of the

coracoid to the point at which the coracoid angulates inferiorly [24]; the coracoid thickness measured in the superoinferior direction 1 cm from the tip of the

coracoid [25]; and the distance from the tip of the coracoid to the base of the

suprascapular notch [26]. The measurement values are shown in Table 1.1.

(From Von Schroeder HP, Kuiper SD, Botte MJ. Osseous anatomy of the scapula.

Clin Orthop 383:131–139, 2001.)

E F

G

TABLE 1.1. MEASUREMENTS OF THE SCAPULA

All Female Male

Sex

Measurementa Figure Average SD Min Max Average SD Min Max Average SD Min Max Difference

General measurements

1 Length of scapula 1-9B 155.0 16.0 127 179 140.8 11.9 127 160 166.4 11.4 143 179 b

2 Post. glenoid–med. scapula distance 1-9B 106.0 8.5 92 122 99.0 3.4 92 103 112.3 5.7 101 122 b

3 Ant. glenoid–med. scapula distance 1-9B,C 106.9 9.7 89 126 98.9 4.5 89 106 113.4 7.8 99 126 b

4 Inferior angle (degrees) 1-9B 36.1 2.5 30 42 34.8 2.1 30 38 36.4 1.6 34 39 b

5 Thickness of medial edge 1-9B 3.8 0.7 3 5 3.6 0.7 3 5 3.9 0.7 3 5 NS

6 Superior glenoid to notch 1-9B 31.8 2.9 28 39 30.6 2.3 28 34 32.6 2.4 29 38 b

Scapular spine

7 Length of spine 1-9C 133.6 11.8 113 153 124.8 5.9 115 136 140.9 10.0 123 153 b

8 Length of base of spine 1-9C 85.5 8.7 71 101 78.5 5.4 71 88 91.1 6.6 78 101 b

9 Spine thickness at 1 cm 1-9C 7.3 1.2 6 10 7.3 1.4 6 10 7.2 1.3 6 10 NS

10 Spine thickness at 4 cm 1-9C 17.9 3.2 11 26 17.0 3.1 11 21 18.3 3.8 14 26 NS

11 Spine thickness laterally 1-9C 46.1 6.3 38 59 41.2 2.2 38 44 50.9 4.9 41 59 b

Acromion

12 Acromial neck diameter 1-9C 13.5 2.2 10 18 12.1 1.0 10 14 14.2 1.7 10 17 b

13 AP length of acromion 1-9D 48.0 5.1 38 57 43.6 3.6 38 51 50.9 3.5 44 57 b

14 ML width of acromion 1-9D 21.9 3.7 15 27 20.4 2.2 17 23 22.6 4.6 15 27 NS

15 Thickness of acromion 1-9D 9.4 1.1 8 12 8.7 0.8 8 10 9.8 0.9 8 11 b

16 Coracoacromial distance 1-9D,E 27.1 4.5 22 39 24.6 2.5 22 29 28.7 5.2 24 39 b

Glenoid and head of scapula

17 Superior glenoid-acromial distance 1-9E 15.5 1.8 13 19 14.9 1.8 13 19 16.1 1.5 14 19 NS

18 AP diameter of glenoid 1-9E 28.6 3.3 25 34 25.8 0.9 25 27 30.9 3.1 25 34 b

19 Diameter of glenoid to notch 1-9E 26.0 2.9 22 32 23.6 0.9 22 25 27.8 3.0 23 32 b

20 SI length of glenoid 1-9E 36.4 3.6 30 43 33.6 1.7 30 36 38.0 3.3 32 42 b

21 Thickness of head at 1 cm 1-9F 22.0 3.5 17 30 19.4 2.2 17 24 24.7 2.8 21 30 b

22 Thickness of head at 2 cm 1-9F 12.9 3.0 8 18 11.0 1.8 8 14 14.5 3.2 8 18 b

23 Glenoid tilt angle (degrees) 1-9F 7.9 3.7 0 17 8.1 3.6 0 14 8.0 3.0 3 13 NS

Coracoid process

24 Length of coracoid 1-9G 45.3 4.7 35 54 42.3 3.0 36 47 48.3 3.4 41 53 b

25 Thickness of coracoid 1-9G 10.6 1.2 8 12 9.8 1.3 8 12 11.4 0.8 10 12 b

26 Distance from coracoid to notch 1-9G 50.7 4.8 40 58 47.7 3.0 40 52 54.0 3.6 48 58 b

aNumbers correspond to those used in figures; all measurements are in millimeters except 4 and 23, which are in degrees.

AP, anteroposterior; Max, maximum; Min, minimum; med, medial; ML, mediolateral; NS, not significant; Post, posterior; SI, superoinferior; SD, standard deviation.

bp < .05.

From von Schroeder HP, Kuiper SD, Botte MJ. Osseous anatomy of the scapula. Clin Orthop 383:131–139, 2001.

the upper portion of the neck of the scapula (see Figs.

1.6–1.8, and 1.9A, D, E, G; Table 1.1). It is located approximately 5.07 cm from the notch of the scapula (26). The

coracoid measures approximately 4.53 cm long and 1.06

cm thick. The base is broad and the anterior portion projects anteriorly. The coracoid process has a concave surface

that faces laterally. It is smooth to accommodate the gliding

of the subscapularis, which passes just inferior to it. The distal portion curves upward to angle more horizontally, and

its outer surface is rough and irregular for attachment of the

pectoralis minor. The pectoralis minor insertion is along the

anterior rim; the coracobrachialis and short head of the

biceps originate more laterally toward the tip. The clavipectoral fascia also attaches to the apex. The attachments of the

trapezoid and conoid ligaments are located just medial to

the pectoralis minor insertion. The coracoid is roughened

along this rim for the ligament and muscle attachments.

The coracoid process usually is palpable through the anterior deltoid, and can be used as a valuable bony landmark

The spine of the scapula spans from the medial border

(at the junction of the upper and middle thirds of the

medial border) of the scapula to the acromion (see Figs. 1.6,

1.7, and 1.9A–C). The length of the spine from the medial

edge to the lateral edge of the acromion is approximately

13.3 cm, with the length of the base 8.5 cm. The anteroposterior width of the spine at 1 and 4 cm from the medial

edge is 7 mm and 18 mm, respectively (26) (Table 1.1). The

upper and lower borders are rough to accommodate muscular attachments. The dorsal border forms the crest of the

spine. The crest of the spine is subcutaneous and easily palpable.

Borders of the Scapula

The scapula has three borders: superior, medial, and lateral

(see Figs. 1.6, 1.7, and 1.9A).

The superior border is the shortest and the bone here is

the thinnest. The edge can be somewhat sharp. The shape

of the border is concave, extending from the medial angle

to the base of the coracoid process. The scapular notch is a

semicircular groove in the rim of the superior border. It is

located at the lateral part of the superior border, with its

base approximately 3.2 cm from the superior rim of the glenoid (26). It is formed partly by the base of the coracoid

process. The superior rim of the suprascapular notch is

crossed by the superior transverse ligament. The ligament

may be ossified. The suprascapular notch has been shown to

exist as an osseous foramen in approximately 13% of specimens (26). The suprascapular nerve passes through the

suprascapular notch, which is transformed into a foramen

by the ligament. This is a potential area of suprascapular

nerve entrapment. The suprascapular artery passes dorsal to

the ligament, and does not enter the notch (28). The portion of the superior border adjacent to the notch also provides attachment for the omohyoid muscle.

The lateral border begins at or above the inferior margin

of the glenoid cavity (see Figs. 1.6, 1.7, and 1.9A). It

inclines obliquely downward and medially to the inferior

angle. Below the glenoid cavity, there is a roughed area, the

infraglenoid tubercle, which is approximately 2.5 cm long.

This area gives origin to the long head of the triceps brachii

muscle. The inferior third of the lateral border is thin and

sharp, and provides attachment of a portion of the teres

major posteriorly. The subscapularis originates anteriorly on

a portion of its anterior surface.

The medial (vertebral) border is the longest of the three

borders of the scapula (see Figs. 1.6, 1.7, and 1.9A). It

extends from the superior angle to the inferior angle. The

border is slightly arched with a posterior convexity. This

border is intermediate in thickness between the superior

and lateral borders, measuring approximately 4 mm thick at

1 cm from the edge (26). The portion superior to the spine

forms an obtuse angle of approximately 145 degrees with

the portion inferior to the spine. The border has an anterior

and posterior lip, with an intermediate narrow area. The

anterior lip provides attachment for the serratus anterior

muscle. The posterior lip provides attachment for the

supraspinatus muscle above the spine and the infraspinatus

below the spine. The narrow area between the two lips provides insertion for the levator scapulae muscle above the triangular area, which marks the beginning of the spine. The

insertion of the levator scapulae may extend along the

major portion of the dorsal rim of the medial border superior to the spine (5,28). The rhomboid minor muscle

inserts on this edge inferior to the levator scapulae at the

level of the spine. The rhomboid major inserts on the rim

just inferior to the attachment of the rhomboid minor (and

inferior to the spine). The insertion of the rhomboid major

may extend along the major portion of the dorsal rim of the

medial border inferior to the spine (5,28). At the level of the

spine, the rhomboid minor also inserts into a fibrous arch

that attaches to the base of the spine.

Angles of the Scapula

The scapula has three angles: the superior, inferior, and lateral angles (see Figs. 1.9A, 1.16, 1.17, 1.19A). The superior

angle is formed by the junction of the superior and medial

(vertebral) borders. This region is thin, smooth, and

rounded, and gives attachment for a portion of the levator

scapulae muscle. It measures approximately 80 degrees.

The inferior angle is formed by the junction of the

medial (vertebral) border and the lateral (axillary) borders.

It measures approximately 25 degrees. The inferior angle, in

contrast to the superior angle, is thick and rough. The dorsal surface provides attachment for the teres major and, in

some individuals, a few fibers of the latissimus dorsi (see

Fig. 1.17).

The lateral angle is the thickest part of the bone, and the

adjacent broadened portion of the bone sometimes is

16 Systems Anatomy

referred to as the head of the scapula. It measures approximately 90 degrees. The broadened area is connected to the

rest of the scapula by a slightly constricted neck. This area

of the scapula forms part of the shoulder joint. The most

lateral portion becomes the glenoid, an oval, slightly concave surface. The surface of the glenoid is relatively shallow.

The mean size of the glenoid is 2.9 cm in anteroposterior

width by 3.6 cm in superoinferior length (26) (Table 1.1).

It faces posteriorly by approximately 8 degrees (26). Its laterally facing articular surface is deepened and broadened by

the glenoid labrum, which is a circumferential rim of fibrocartilage. The glenoid labrum plays an important role in

stabilizing the shoulder. Superior to the glenoid, near the

base of the coracoid process, there is a slight elevation, the

supraglenoid tubercle, which provides the origin of the long

head of the biceps brachii.

Associated Joints

The scapula articulates with the acromial end of the clavicle

at the acromioclavicular articulation (see earlier, under

Clavicle), and articulates with the proximal humerus at the

glenoid articulation. The scapula slides and rotates on the

thorax, stabilized by muscular attachments, and forms the

soft tissue scapulothoracic articulation.

Muscle Origins and Insertions

Muscle attachments include the trapezius, deltoid (deltoideus), supraspinatus, infraspinatus, levator scapulae,

minor and major rhomboids (rhomboideus), serratus anterior, teres major, teres minor, subscapularis, triceps, long

and short heads of the biceps, coracobrachialis, pectoralis

minor, and the omohyoid (see Figs. 1.6 and 1.7). The costal

(anterior) surface provides the origin for the subscapularis.

The dorsal (posterior) surface provides the origins for the

supraspinatus (from the supraspinatus fossa) and infraspinatus (from the infraspinatus fossa). The spine contains

part of the insertion of the trapezius as well as a portion of

the origin of the deltoid. The dorsal portion of the

acromion contains additional areas for the origin of the deltoid. The coracoid process contains the origins of the coracobrachialis and the short head of the biceps as well as the

insertion of the pectoralis minor. The dorsal rim of the

medial (vertebral) border receives the insertions of the levator scapulae and the minor and major rhomboid muscles.

The levator scapulae insertion is located superior to the

level of the spine, the rhomboideus minor insertion is

located at the level of the spine, and the superior rhomboideus major insertion is located inferior to the level of the

spine. The serratus anterior inserts along the anterior

(costal) surface of the medial border. The teres minor and

the teres major originate along the dorsal rim of the lateral

border. The teres minor origin lies superior to the teres

major. The origin of the long head of the triceps is located

inferior to the glenoid. The long head of the biceps originates superior to the glenoid. The omohyoid inserts on the

upper rim of body, superior to the supraspinatus fossa.

Clinical Correlations: Scapula

Failure of Bony Union

Congenital failure of bony union between the acromion

and spine may occur. The junction may be stabilized by

fibrous tissue or may exist as a defect in the scapula. This

may be mistaken for a fracture of the acromion, when in

reality it represents a chronic fibrous union.

Os Acromiale

The base of the acromion is formed from three or four ossification centers. Persistence of one of the individual ossification centers of the acromion that does not fuse with the

others or with the scapula can present as an accessory bone,

the os acromiale. The os acromiale can be mistaken for a

fracture of the acromion or humerus, or can resemble calcific tendinitis of the supraspinatus tendon. The os acromiale usually can be detected because it usually is located at

the lateral margin of the acromion; it is of variable size and

shape but usually is rounded and bilateral (25). It may exist

as a small accessory ossicle directly above the greater

tuberosity of the humerus, separated from the acromion by

approximately 1 cm, and usually is somewhat circular (25).

The Acromion as a Bony Landmark

The lateral border of the acromion usually is palpable. It

allows orientation for operative procedures in the vicinity of

the subdeltoid bursa or rotator cuff.

The Acromion’s Role in Impingement

Syndrome

Impingement of the rotator cuff usually involves thickening

of the acromion. The portion that usually is most thickened

or responsible for impingement is the anterior portion,

which often develops an exostosis or large osteophyte.

The Coracoid Process as a Bony Landmark

With the arm by the side, the tip of the coracoid process

is oriented anteriorly. It can be palpated by applying deep

pressure through the anterior portion of the deltoid muscle approximately 2.5 cm below the lateral part of the

clavicle on the lateral side of the infraclavicular fossa.

Because muscles (pectoralis minor, short head biceps,

coracobrachialis) and ligaments (coracoclavicular and

coracoacromial ligaments) attach to the coracoid process,

and because of the close vicinity of the musculocutaneous

1 Skeletal Anatomy 17

nerve, the coracoid is a valuable palpable landmark for orientation in terms of these structures. The coracoid process

also serves as a valuable landmark for operative approaches

to the glenohumeral joint and the brachial plexus. In addition, the base of the coracoid process forms a portion of

the suprascapular notch. It can be a potential aid in the

localization of the suprascapular nerve and suprascapular

notch.

Suprascapular Nerve Entrapment

The suprascapular notch is converted to a foramen by the

attachment of the superior transverse ligament, which

crosses across the upper open end of the notch (29,30). The

ligament may be ossified. [The suprascapular notch has

been shown to exist as an osseous foramen in approximately

13% of specimens (26).] The suprascapular nerve passes

through the notch, and is susceptible to nerve compression

in this area. This condition occasionally is seen in patients

with inflammatory conditions or in young, active athletes

and is characterized by localized pain or atrophy of the

supraspinatus and infraspinatus. Treatment includes conservative management (antiinflammatory medications, possible cortisone injections, and activity modification). If it is

refractory to medical treatment or if localized atrophy is

present, operative nerve decompression usually is warranted.

Winging of the Scapula

Winging of the scapula is a deformity in which the scapula

angles up from the thorax (scapula alta), usually due to

muscular imbalance. It often is caused by neuropathy of the

long thoracic nerve and weakness of the serratus anterior, or

by neuropathy of the spinal accessory nerve with weakness

of the trapezius muscle (30,31).

HUMERUS

Derivation and Terminology

Humerus is derived from the Latin humer, meaning “shoulder” (3). The plural of humerus is humeri.

Ossification Centers

The humerus has eight ossification centers: one each for the

body, the head, the greater tuberosity, the lesser tuberosity,

the capitulum, and the trochlea, and one for each epicondyle (Fig. 1.10). The ossification center for the body

appears near the central portion of the bone at approximately the eighth week of fetal life. Ossification soon

extends to either end of the bone, so that at birth the

humerus is nearly completely ossified, with only the ends

remaining cartilaginous.

In the proximal end of the humerus, ossification begins

in the head of the bone during the first year (or earlier in

some individuals). The center for the greater tuberosity

begins to ossify during the third year, and the center for the

lesser tuberosity begins to ossify during the fifth year. The

centers for the head and tuberosities usually join by the

sixth year, forming a single large epiphysis that fuses with

the body in approximately the twentieth year (see Fig.

1.10B).

In the distal end of the humerus, ossification begins in

the capitulum near the end of the second year and extends

medially to form the major part of the articular end of the

bone. The center for the medial part of the trochlea appears

at approximately 10 years of age. The medial epicondyle

begins to ossify at approximately the fifth year, and the lateral epicondyle at approximately the twelfth or thirteenth

year. The lateral epicondyle and both portions of the articulating surface (having already joined together) unite with

the body. At approximately the eighteenth year, the medial

epicondyle is joined to the body of the humerus.

Osteology of the Humerus

The humerus is the largest bone in the upper extremity.

Each end of the humerus is composed of cancellous bone

covered by thin cortical bone. The diaphysis consists of

thick cortical bone throughout its length, with a well

defined medullary canal. The medullary canal extends the

entire length of the humerus. At the proximal and distal

metaphyses, the medullary canal changes to cancellous

bone, and the outer cortex becomes thinner (Figs 1.11 to

1.13).

For descriptive osteology, the humerus can be described

in terms of the proximal end, the shaft (diaphysis or body),

and the distal end (Fig. 1.14; see Figs 1.11 to 1.13). The

proximal end consists of the head, anatomic neck, surgical

neck, and the greater and lesser tuberosities. The distal end

includes the capitulum, trochlea, and medial and lateral

condyles and epicondyles.

Proximal End of the Humerus

The head of the humerus forms nearly half of a sphere (see

Figs. 1.11 to 1.13). With the arm at the side of the body,

the humeral head is directed medially, superiorly, and

slightly posteriorly, thus facing the glenohumeral joint. The

entire smooth area, covered by hyaline cartilage, articulates

with the glenoid of the scapula.

The anatomic neck of the humerus denotes an obliquely

oriented margin or circumference line that extends along

and inferior to the articular portion of the head (see Figs.

1.11 and 1.12). In this area there is a groove that encircles

the articular portion. The groove is well delineated along

the inferior half. In the superior portion, the groove narrows to separate the head from the greater and lesser

18 Systems Anatomy

1 Skeletal Anatomy 19

FIGURE 1.10. A: Illustration of humerus showing centers of

ossification. There are eight ossification centers: one each

for the shaft, the head, the greater tuberosity, the lesser

tuberosity, the capitulum, and the trochlea, and one for

each epicondyle. B: Schematic illustration of proximal and

distal humerus in a young adult showing epiphyseal lines.

The dark lines indicate the attachment of the articular capsule.

A B

tuberosities. The circumference of the anatomic neck provides attachment for the articular capsule of the shoulder

joint. In this area, there are numerous foramina for nutrient

vessels (4).

The surgical neck is located distal to the anatomic neck

(see Figs. 1.11 and 1.12). It is the area of the junction of the

shaft with the proximal end of the humerus, just distal to

the head and tuberosities. As opposed to the anatomic neck,

there is no groove that delineates the surgical neck. Its name

derives from the common occurrence of fractures in this

area, many of which are managed by operative methods.

The greater tuberosity is located lateral to the head and

lateral to the lesser tuberosity (see Figs. 1.11 to 1.13). The

greater tuberosity often is referred to as the greater tubercle

in anatomy textbooks (4,5). The upper surface is rounded

and contains three flat impressions for muscle insertion.

The superiormost portion of the greater tuberosity provides

insertion for the supraspinatus. The middle impression is

for the infraspinatus, and the inferiormost impression for

the teres minor. The insertion site for the teres minor lies

approximately 2.5 cm distal to the insertion of the

supraspinatus, and a portion of the teres minor inserts onto

the shaft. The lateral surface of the greater tuberosity is

rough and convex. It merges distally into the lateral surface

of the shaft of the humerus.

The lesser tuberosity is smaller but more prominent than

the greater tuberosity (see Figs. 1.12 to 1.13). The lesser

tuberosity often is referred to as the lesser tubercle in

anatomy textbooks (4,5). It is located anteriorly, adjacent to

the anatomic neck. The anterior surfaced of the lesser

tuberosity provides the major points of insertion of the subscapularis.

The greater and lesser tuberosities are separated from

each other by a deep groove, the bicipital groove (intertubercular groove, intertubercular sulcus; see Figs. 1.12 and

1.13A). The tendon of the long head of the biceps brachii

muscle coursers along and within this groove, along with a

branch of the anterior humeral circumflex artery, which

travels superiorly to supply a portion of the shoulder joint.

The bicipital groove courses obliquely downward and ends

in the proximal third of the humeral shaft. The upper portion of the bicipital groove is lined by a thin layer of cartilage and covered by an extension of the synovial membrane

of the shoulder. The lower portion of the groove becomes

progressively shallow and provides the insertion of the latissimus dorsi. On either side of the bicipital groove there is a

crest of bone. These are the crests of the greater and lesser

tuberosities, also known as the bicipital ridges. Distal to the

greater and lesser tuberosities, the circumference of the

bone narrows to where the shaft joins the proximal portion.

This is the surgical neck of the humerus. In the distal portion of the bicipital groove, the latissimus dorsi inserts just

medial to the groove. The pectoralis major tendon inserts

just lateral to the groove, slightly distal to the insertion of

the latissimus dorsi.

20 Systems Anatomy

FIGURE 1.11. Right humerus, posterior aspect.

1 Skeletal Anatomy 21

FIGURE 1.12. Right humerus, anterior aspect.

22 Systems Anatomy

FIGURE 1.13. A: Right humerus, anterior aspect, showing muscle origins and insertions. B: Right

humerus, posterior aspect, showing muscle origins (red) and insertions (blue).

A B

Shaft of the Humerus

The shaft of the humerus, also anatomically referred to as

the body, spans the portion of the humerus from the surgical neck proximally and to the area just proximal to the portion referred to as the distal extremity (see Figs. 1.11 to

1.13). (The distal extremity includes the condyles, capitulum, and trochlea, as discussed later.) The shaft of the

humerus is cylindrical in the proximal portion, but

becomes progressively flatter and somewhat triangular distally. In the distal portion of the shaft, the bone actually has

three surfaces, but two borders (the medial and lateral borders).

The surfaces of the shaft of the humerus consist of an

anterolateral surface, an anteromedial surface, and a posterior (or dorsal) surface. The anterior surface is divided into

the anterolateral and anteromedial surfaces by an oblique

ridge that starts proximally and laterally at the greater

tuberosity and extends distally to end near the medial epicondyle.

The anterolateral surface of the proximal humeral shaft

provides the elongated insertion area of the pectoralis major

muscle, which attaches along the distal part of the crest of

the greater tuberosity (see earlier, under The Proximal End

of the Humerus). Lateral and distal to the insertion of the

pectoralis major is an oblong area that provides the insertion point of the deltoid muscle. This area, known as the

deltoid tuberosity, is located on the anterolateral surface of

the humerus and consists of a raised, slightly triangular elevation. Distal and anterior to the deltoid tuberosity, extending along the anterolateral surface of the humeral shaft,

there is a relatively large, broad, slightly concave area that

provides the origin area for the brachialis. Also distal to the

deltoid tuberosity is the radial sulcus (radial groove), which

extends obliquely distally, spiraling along the lateral shaft,

and provides the path for the radial nerve and profunda

brachii artery (see Figs. 1.11 and 1.13B). The radial sulcus

is bordered on one side by the origin of the lateral head of

the triceps, the deltoid tuberosity, and the origin of the

brachialis (all located lateral and proximal to the groove).

On the other side of the radial sulcus is the origin of the

medial head of the triceps, located medial and distal to the

sulcus.

The anteromedial surface of the humeral shaft contains

a portion of the bicipital groove proximally. The tendon of

the latissimus dorsi inserts into or along the medial crest of

the intertubercular groove in the area just distal to that traversed by the bicipital tendon. Distal and medial to this area

near the medial border, is the insertion area of the teres

major. In the midportion of the anteromedial shaft, near

the medial border of the humerus is the insertion area of the

coracobrachialis. In the distal portion of the anteromedial

surface of the humerus, the bone is flat and smooth, and

provides for the large origin of the brachialis muscle.

The dorsal surface of the humerus slightly rotates from

proximal to distal, so that the proximal portion is directed

slightly medially, and the distal portion is directed posteriorly and slightly laterally. The surface of the posterior surface of the humerus is nearly completely covered by the lateral and medial heads of the triceps brachii. The lateral head

arises from the proximal portion, on the lateral half of the

bone, just lateral to the radial sulcus. The origin of the

medial head of the triceps begins on the proximal third of

the posterior surface of the humerus, along the medial border of the bone and the medial distal border of the radial

sulcus. This large origin area extends the length of the posterior humerus, covering the major portion of the posterior

half of the humerus. The triceps origin extends distally to

end as far as distal as the posterior portion of the lateral epicondyle, just proximal to the origin of the anconeus muscle.

The medial and lateral borders run the entire length of

the humerus. The medial border of the humerus extends

from the lesser tuberosity to the medial epicondyle. The

proximal third of the medial border consists of a prominent

crest, the crest of the lesser tuberosity. The crest of the lesser

tuberosity provides the insertion area of the tendon of the

teres major. More distally, in the mid-portion of the shaft

and located on the medial border is a rough impression for

the insertion of the coracobrachialis. Distal to this area is

the entrance of the nutrient canal into the humerus. A second nutrient canal may exist at the starting point of the

1 Skeletal Anatomy 23

FIGURE 1.14. Distal humerus, inferior surface, showing

articular surface and contours of trochlea and capitulum.

radial sulcus. The anterior portion of the distal third provides the origin area for the brachialis muscle (see above

under shaft of the humerus). The posterior portion of the

distal third and medial border of the medial and distal

thirds of the shaft provide the wide origin area of the medial

head of the triceps. The distal third of the medial border is

raised into a ridge, the medial supracondylar ridge. This

ridge becomes more prominent distally. The medial supracondylar ridge provides an anterior lip for a portion of the

origin of the brachialis muscle. The ridge also provides a

posterior lip for a portion of the medial head of the triceps

brachii. The medial intermuscular septum attaches in an

intermediate portion of the medial supracondylar ridge.

The lateral border of the humerus extends from the dorsal part of the greater tuberosity to the lateral epicondyle.

The lateral border separates the anterolateral surface of the

humerus from the posterior surface. The proximal half of

the lateral border is rounded and indistinctly marked, serving for the attachment of part of the insertion of the teres

minor, and the origin of the lateral head of the triceps

brachii. The sulcus or groove for the radial nerve (see above)

crosses the central portion of the lateral border of the

humerus. The distal part of the lateral border forms a

rough, prominent margin, the lateral supracondylar ridge.

The lateral supracondylar ridge provides the attachment

area for several structures. Superiorly, there is an anterior lip

for the origin of the brachioradialis muscle. Distal to this

area, the lateral supracondylar ridge provides an area for the

origin for the extensor carpi radialis longus. Distally, there

is a posterior lip for a portion of the origin of the medial

head of the triceps brachii. The intermediate portion of the

lateral supracondylar ridge provides the attachment site for

the lateral intermuscular septum.

Distal Portion of the Humerus

The distal portion of the humerus is often referred anatomically as the distal extremity of the humerus (see Figs. 1.11

to 1.14). The distal portion is flat, widened, and ends distally in a broad, articular surface. The distal portion contains the two condyles, medial and lateral (see Fig. 1.14).

The lateral portion of the distal articular part consists of a

smooth, somewhat semi-spherical shaped capitulum of the

humerus. The capitulum is covered with articular cartilage

on its anterior surface and articulates with the fovea of the

head of the radius. Proximal to the capitulum, there is a

slight depression in the humerus, the radial fossa. The radial

fossa provides a space for the anterior border of the head of

the radius when the elbow is fully flexed. Just medial to the

capitulum is a slight shallow groove, in which the medial

margin of the head of the radius articulates. Just proximal

to the capitulum on the anterior surface of the humerus are

several small foramina for nutrient vessels.

The medial side of the articular surface of the distal

humerus is comprised of the spool-shaped trochlea (see

Fig. 1.14). The trochlea occupies the anterior, inferior,

and posterior surfaces of the condyle. The trochlea has a

deep groove between two well demarcated borders. The

lateral border is separated from the capitulum by the shallow groove. The medial border of the trochlea is thicker,

wider, and more prominent, and projects more distally

than the lateral border. The grooved portion of the articular surface of the trochlea is shaped well to fit the articular surface of the trochlear notch of the ulna. The trochlea

is wider and deeper on the dorsal surface than on the anterior surface. Proximal to the anterior portion of the

trochlea is a small depression, the coronoid fossa. The

coronoid fossa provides a space for the coronoid process of

the ulna during flexion of the elbow. Proximal to the posterior part of the trochlea is a deep, triangular depression,

the olecranon fossa. The olecranon fossa provides a space

to accept the most proximal portion of the olecranon

when the elbow is extended. The olecranon fossa and the

coronoid fossa are separated from each other by a thin,

sometimes translucent partition of bone. The partition

may be perforated to produce a supratrochlear foramen.

The fossae are lined by a synovial membrane that extends

from the elbow joint. The margins of the fossae provide

attachment for the anterior and posterior ligaments and

joint capsule of the elbow.

Above the medial and lateral condyles are the epicondyles. These projections provide the attachment for several muscles. The medial epicondyle is larger and more

prominent than the lateral epicondyle. The medial epicondyle contains the origin of the extrinsic flexor pronator

muscles of the forearm and flexor muscles of the hand and

wrist. These include the pronator teres, flexor carpi radialis,

palmaris longus, flexor digitorum superficialis, flexor digitorum profundus, and flexor carpi ulnaris. The ulnar collateral ligaments of the elbow joint also originate from the

medial epicondyle. On the posterior surface of the medial

epicondyle is a shallow groove in which the ulnar nerve traverses.

The lateral epicondyle is smaller and less prominent than

the medial epicondyle. The lateral epicondyle contains the

origin of several muscles, including the wrist and digit

extrinsic extensor muscles and the supinator. Muscle attachments to the lateral epicondyle include the supinator, extensor carpi radialis longus, extensor carpi radialis brevis,

extensor digitorum communis, extensor carpi ulnaris, extensor digiti minimi, and anconeus. The lateral epicondyle also

provides attachment for the radial collateral ligament of the

elbow joint

Associated Joints

The humerus articulates with the scapula at the glenohumeral joint, with the ulna at the ulnohumeral joint

(trochleoulnar joint), and with the radius at the radiocapitellar joint.

24 Systems Anatomy

Muscle Origins and Insertions

Muscle attachments include 24 muscles (see Figs. 1.13A–B).

The greater tuberosity provides the insertion of the

supraspinatus, the infraspinatus, and the teres minor. The

lesser tuberosity affords the insertion of the subscapularis.

The pectoralis major inserts to the anterior bicipital groove,

the teres major inserts to the posterior bicipital groove, and

the latissimus dorsi inserts to the central portion or crest of

the bicipital groove. The shaft of the humerus provides the

insertion of the deltoid and coracobrachialis, and the origins

of the brachialis and the triceps (medial and lateral heads).

The lateral shaft and epicondyle is the area of origin of the

brachioradialis; the medial epicondyle provides the origin of

the pronator teres, the flexor carpi radialis, the palmaris

longus, the flexor digitorum superficialis, the flexor digitorum profundus, the flexor carpi ulnaris, and the anconeus.

The lateral epicondyle provides origin for the extensor carpi

radialis longus and brevis, the extensor digitorum communis,

extensor digiti minimi, extensor carpi ulnaris, and anconeus.

Clinical Correlations: Humerus

The Surgical Neck

The surgical neck, located at the junction of the head (and

tuberosities) with the shaft, is an area of frequent fracture,

hence its name. Fractures of the surgical neck are much

more common than in the anatomic neck, and usually are

the result of a direct impact or a fall onto the elbow with the

arm abducted. Deformity of fractures of the surgical neck

usually include adduction or medial displacement of the

shaft due to the pull of the pectoralis major, teres major, and

latissimus dorsi. The proximal fragment may be abducted

by the pull of the supraspinatus muscle.

The Anatomic Neck

Fractures rarely occur along the anatomic neck. When fractures do occur in this location, it usually is in an older

patient and often is the result of a fall onto the shoulder.

Because the shoulder capsule attaches to the bone distal to

the anatomic neck, fractures of the anatomic neck usually

are intracapsular.

Impingement Syndrome

Impingement syndrome of the shoulder refers to a condition in which the supraspinatus tendon and subacromial

bursa are chronically or repetitively entrapped between the

humeral head inferiorly and either the anterior acromion

itself, spurs of the anterior acromion or acromioclavicular

joint, or the coracoacromial ligament superiorly (17).

Osseous findings seen radiographically can include thickening or proliferation of the acromion, spurring at the

anteroinferior aspect of the acromion, degenerative changes

of the humeral tuberosities at the insertion of the rotator

cuff, or a humeral head that is slightly superiorly located or

mildly superiorly subluxated. Magnetic resonance imaging

(MRI) can demonstrate soft tissue changes such as bursal

inflammation, thickening and effusion, and inflammatory

changes or partial tearing of the rotator cuff before osseous

changes seen by standard radiographs (17).

Neer Classification of Impingement Syndrome

(32)

n Stage I: Local edema or hemorrhage; reversible condition. Usual age group: young, active individuals involved

in sports requiring excessive overhead use of arm.

n Stage II: Fibrosis, thickening of subacromial soft tissue,

rotator cuff tendinitis, and possible partial tear of rotator

cuff; manifested by recurrent pain. Usual age group: 25

to 40 years.

n Stage III: Complete rupture of rotator cuff, progressive

disability. Usual age group: over 40 years.

Fractures of the Proximal Humerus

Neer has classified fractures of the proximal humerus as to

the number of segments (18):

n One-part fractures of the proximal humerus are fractures

with minimal or no displacement or angulation.

n Two-part fractures consist of two major displaced fragments. This can include a displaced fracture of either the

greater or lesser tuberosity, fracture of the surgical neck,

or fracture of the anatomic neck.

n Three-part fractures consist of three major displaced

fragments. This can include fractures of both the greater

and lesser tuberosities, or a combination of fracture of

one of the tuberosities and fracture of the surgical neck.

n Four-part fractures consist of four displaced fragments,

such as those involving both tuberosities as well as the

surgical neck.

Anterior Dislocation of the Shoulder

In this injury, the humeral head dislocates anterior to the

glenoid; it accounts for 97% of shoulder dislocations. It

usually is diagnosed on anteroposterior radiographs. Definitive radiographic diagnosis is by the transscapular (“Y”

view) or axillary view.

Hill-Sacks Lesion

This is a defect in the posterolateral aspect of the humeral

head resulting from anterior dislocation (often associated

with recurrent injuries). The lesion occurs when the dislocated humeral head strikes the inferior margin of the glenoid, producing a “hatchet” compression fracture defect of

the humeral head. It usually is demonstrated on the antero1 Skeletal Anatomy 25

posterior view radiograph of the shoulder with the humerus

internally rotated. The presence of this lesion is virtually

diagnostic of previous anterior dislocation (17).

Bankart Lesion

Injury to the anterior-inferior cartilaginous labrum, which

is usually associated with an avulsion of the inferior glenohumeral ligament from the anterior-inferior glenoid rim.

Associated from anterior dislocation of the glenohumeral

joint. It may affect only fibrocartilaginous portion of the

glenoid, but is commonly noted in association with a fracture of the anterior aspect of the inferior osseous rim of the

glenoid. The Bankart lesion is less commonly seen than the

Hill-Sacks lesion. The presence of this lesion is virtually

diagnostic of previous anterior dislocation (17).

Posterior Dislocation of the Shoulder

This accounts for 2% to 3% of shoulder dislocations. It can

occur from direct force or a blow to the anterior shoulder,

from indirect force applied to the arm combining adduction,

flexion, and internal rotation, or it can be associated with

severe muscle contraction from electric shock or convulsive

seizures. The humeral head is located posterior to the glenoid

fossa, and usually impacts on the posterior rim of the glenoid.

The shoulder usually is positioned or locked in adduction

and internal rotation. Standard radiographs may not demonstrate the lesion (because the humeral head lies directly posteriorly, and radiographs may appear unremarkable on standard anteroposterior views). Injury can be demonstrated by

either an axillary view (often difficult to obtain because of the

arm locked in adduction) or by a special anteroposterior view

with the patient rotated 40 degrees toward the affected side.

With this view, the normal clear space of the glenohumeral

joint is obliterated by the overlap of the humeral head located

posterior and slightly medial to the surface of the glenoid.

Fractures of the Shaft Proximal to the

Insertion of the Deltoid Muscle

If a fracture of the humeral shaft occurs just proximal to the

insertion of the deltoid, the proximal fragment of the

humerus usually is adducted or pulled medially by the pectoralis major, latissimus dorsi, and teres major. The distal

fragment usually is displaced or angulated laterally (apex

medially, or fracture in valgus) because of the deltoid.

Fractures of the Humeral Shaft Distal to the

Insertion of the Deltoid Muscle

If a fracture of the humeral shaft occurs just distal to the

insertion of the deltoid, the proximal fragment usually is

displaced laterally by the deltoid and supraspinatus muscle.

The distal fragment usually is pulled medially and upward

by the triceps, biceps, and the coracobrachialis muscles.

Fractures of the Humeral Shaft Associated

with Radial Nerve Palsy

Up to 18% of humeral shaft fractures have an associated

radial nerve injury (33–36). Most nerve injuries represent a

neurapraxia or axonotmesis, and 90% resolve in 3 to 4

months (37–39). This injury often is referred to as the Holstein-Lewis fracture, which describes an oblique fracture of

the distal third of the humerus. However, radial nerve palsy

is associated most commonly with fractures of the middle

third of the humerus (34,38).

Supracondylar Fractures

The area of bone at the supracondylar level is relatively thin,

and fractures through this area are common, especially in

children. Structures at risk for injury in supracondylar fractures include the brachial artery and median nerve anteriorly and the radial nerve laterally. Brachial artery injury

subsequently is associated with compartment syndrome of

the forearm.

Supracondylar Process

In approximately 1% of upper extremities, there is a downward-curved, hook-shaped process of bone that emanates

from the medial cortex approximately 5 cm proximal to the

medial epicondyle. It can be associated with a connecting

fibrous band (ligament of Struthers), which can be a proximal extension of the pronator teres. The median nerve may

pass deep to the supracondylar process and ligament, and

may be subject to compression, resulting in median neuropathy. The brachial artery also may pass deep to the ligament (28,40–43).

Lateral Epicondylitis

Lateral epicondylitis commonly is referred to as tennis

elbow. It is thought to consist of either chronic inflammation, partial tear, or “overuse injury” of the common extensor origin. Chronic or repetitive wrist or digital extension

often is associated with the onset of symptoms. The extensor carpi radialis brevis often is implicated as the main muscle involved. Although management usually is conservative

(activity modification, antiinflammatory medications,

splinting, cortisone injections), severe and refractory cases

can be managed with operative exploration and release,

debridement, or repair of the extensor carpi radialis brevis

origin or other involved muscle.

Medial Epicondylitis

Medial epicondylitis commonly is referred to as golfer’s

elbow. Similar to lateral epicondylitis, it is though to consist

of either chronic inflammation, partial tear, or overuse

injury of the common flexor pronator muscle origin.

26 Systems Anatomy

Chronic or repetitive wrist or digital flexion often is associated with symptoms.

Osteochondrosis

Osteochondrosis (osteochondritis dissecans, osteonecrosis)

of the capitellum of the humerus is referred to as Panner’s

disease.

ULNA

Derivation and Terminology

The ulna derives its name from the Latin word meaning “the

arm” or “the elbow” (1,3). The plural of ulna is ulnae (1).

Ossification Centers and Accessory Bones

The ulna has three ossification centers: one in the shaft

(body), one in the proximal portion (proximal extremity),

and one in the distal end (distal extremity). The mid-portion of the shaft is the first ossification center to appear,

becoming visible at approximately the eighth week of fetal

life (Figs. 1.15 and 1.16). The ossification centers then

extend through the major part of the shaft. At birth, the

distal portions and the major part of the olecranon remain

cartilaginous. Between the fifth and sixth years, a center in

the central portion of the ulnar head appears and soon

extends into the styloid process. At approximately the

tenth year, a center appears in the olecranon near its outer

portion. Most of the ossification of the olecranon actually

develops from proximal extension from the center of the

shaft (2,4,5).

Several accessory bones can be associated with the distal

ulna. These accessory bones, if present, usually are the result

of secondary or additional ossification centers that do not

fuse with the distal ulnar or associated carpal bones. Accessory bones associated with the distal ulna include the os triangulare (os intermedium antebrachii, os triquetrum secundarium), the os ulnostyloideum, and the os pisiforme

secundarium (ulnare antebrachii, metapisoid) (see Fig.

1.27B) (44–46). The os triangulare is located distal to the

head of the ulna, between the ulnar head, lunate, and triquetrum. The os ulnostyloideum is located in the vicinity

of the ulnar styloid. The os pisiforme secundarium is

located between the distal ulna and pisiform, close to the

proximal edge of the pisiform.

1 Skeletal Anatomy 27

FIGURE 1.15. Illustration of ulna, showing the three centers of

ossification. There is one center in the shaft (body), one in the

proximal portion (proximal extremity), and one in the distal end

(distal extremity).

FIGURE 1.16. Illustration of proximal and distal ulna in a young

adult, showing epiphyseal lines.

Accessory bones also can occur from other causes such as

trauma (46) or heterotopic ossification of synovial tags (47).

Therefore, anomalous, irregular ossicles or small, rounded

bones of abnormal size or shape may be encountered that

do not fit a specific described accessory bone or location.

Osteology of the Ulna

The ulna is located in the medial aspect of the forearm lying

parallel to the radius when the forearm is supinated. It is a

true long bone with a triangular cross-section proximally

that becomes rounded distally. The ulna consists of a shaft

with thick cortical bone and a long, narrow medullary canal

(Figs. 1.17 to 1.20). The cortex of the ulna is thickest along

the interosseous border and dorsal surface. In the proximal

and distal ends of the ulna, the cortical bone becomes thinner, and the medullary canal is replaced with cancellous

bone. The cortical bone remains relatively thick along the

posterior portion of the olecranon.

The ulna is anatomically divided into three main portions: the proximal end (proximal portion, proximal

extremity), the shaft (body), and the distal end (distal portion, distal extremity) (Fig. 1.21; see Figs. 1.19 and 1.20).

The proximal end contains the hook-shaped olecranon and

the coronoid process to form the medial hinge-like portion

of the elbow. The shaft consists of the major portion of the

body between the proximal and distal portions. The distal

end consists of the head and styloid process. In general, the

ulna becomes progressively smaller and thinner from proximal to distal.

Proximal Ulna

The proximal end of the ulna consists of the olecranon, the

coronoid process, the trochlear notch, and the radial notch

(see Fig. 1.21A–F).

The olecranon is the large, thick curved portion of the

proximal ulna. The most proximal portion of the olecranon

is angled slightly forward or distally to form a prominent lip

that passes into the olecranon fossa of the humerus when

the elbow is extended. The base of the olecranon is slightly

constricted where it joins the shaft of the ulna, forming the

narrowest part of the proximal ulna. The posterior surface

of the olecranon is triangular and smooth. This prominent

area, easily palpable through the skin, is covered by the olecranon bursa. The superior (or most proximal) surface of

the olecranon is somewhat quadrilateral in shape and has a

rough surface for the insertion of the triceps tendon. The

anterior surface of the olecranon is concave and smooth,

and is lined with articular cartilage to form the proximal

portion of the trochlear notch. There usually is a nonarticular zone in the mid-portion of the articular surface (see

later discussion of trochlear notch). The elbow joint capsule

attaches to the anterior aspect of the superior surface of the

olecranon. The medial portion of the olecranon provides

attachment for the oblique and posterior parts of the ulnar

collateral ligament. The medial aspect of the olecranon also

provides an area for the origin of a portion of the flexor

carpi ulnaris muscle. The posteromedial portion also provides a part of the origin of the flexor digitorum superficialis. The lateral portion of the olecranon provides the

insertion of the anconeus muscle (see Fig. 1.18).

28 Systems Anatomy

FIGURE 1.17. Right ulna and radius, anterior aspect, showing

muscle origins (red) and insertions (blue).

The coronoid process is a triangular eminence that projects from the anterior surface of the ulna, roughly at the

junction of the shaft with the proximal portion (see Fig.

1.19). Its base arises from the proximal and anterior part

of the shaft. The superior surface of the coronoid process

is smooth and concave, and forms the inferior portion of

the trochlear notch. Its inferior surface is concave and

rough. At the junction of the coronoid with the shaft of

the ulna is a thickened, rough eminence, the tuberosity of

the ulna. This tuberosity provides the attachment area for

the brachialis as well as the oblique cord of the radius. The

lateral surface of the coronoid contains the radial notch,

1 Skeletal Anatomy 29

FIGURE 1.18. Right ulna and radius, posterior aspect, showing

muscle origins (red) and insertions (blue).

FIGURE 1.19. Right ulna and radius, anterior aspect.

which is a narrow, rounded, oblong depression lined with

articular cartilage. The radial notch articulates with the

rim of the radial head during forearm supination and

pronation. The medial surface of the coronoid process

provides the area of attachment of the anterior and

oblique portions of the ulnar collateral ligament. At the

anterior portion of the medial surface of the coronoid is a

small, rounded eminence for the origin of three humeroulnar heads of the flexor digitorum superficialis. Posterior to this eminence, a slight ridge extends from the

medial aspect of the coronoid distally. Along this ridge

arise the proximal portions of the insertions of the flexor

digitorum profundus, along with the ulnar head of the

pronator teres. In addition, a small ulnar head of the

flexor pollicis longus may arise from the distal part of the

coronoid process (see Fig. 1.17).

30 Systems Anatomy

FIGURE 1.20. Right ulna and radius, posterior aspect.

The trochlear notch of the ulna is a large concave depression that is semilunar in shape and formed by the coronoid

process and the olecranon (see Figs. 1.19 and 1.21A,E, and

F). The trochlear notch, covered anteriorly by articular cartilage, provides the articular surface for the trochlea of the

humerus. The articular surface of the trochlear notch has an

area near its mid-portion that contains a central transverse

area that usually is deficient in articular cartilage. This area

subdivides the articular surface into a proximal portion (on

the anterior surface of the olecranon) and a distal portion

(on the anterosuperior surface of the coronoid). At this

mid-portion of the trochlear notch, the borders are slightly

indented near its middle, creating a narrow portion in the

proximal ulna.

The radial notch of the ulna is the articular depression

on the lateral aspect of the coronoid process (see Figs. 1.19,

1 Skeletal Anatomy 31

FIGURE 1.21. A: Proximal right ulna, lateral aspect. B: Right elbow, medial aspect, showing capsular attachment and medial ligaments. C: Right elbow, lateral aspect, showing capsular attachment and lateral ligaments. D: Right elbow, sagittal section. E: Proximal radioulnar joint, with

radial head removed, showing annular ligament.

(continued on next page)

A B

C D

32 Systems Anatomy

FIGURE 1.21. (continued) E: Proximal radioulnar joint, with radial head removed, showing

annular ligament. F: Proximal ulna, with proximal radius removed to show annular ligament and

radial notch. G: Right elbow, anterior aspect, showing synovial membrane. The capsule has been

removed and the articular cavity distended. H: Right elbow, posterior aspect, showing synovial

membrane. The capsule has been removed and the articular cavity distended.

E F

G H

and 1.21A,E, and F). The notch is narrow, oblong, and

lined with articular cartilage. The notch articulates with the

circumferential rim of the radial head. The anterior and

posterior margins of the radial notch provide the attachment areas for the annular ligament.

Shaft (Body) of the Ulna

The shaft (or body) of the ulna is triangular in cross-section

in the proximal two-thirds, but becomes round in the distal

third. Longitudinally, the proximal half of the shaft is

slightly convex dorsally and concave anteriorly. The distal

half (and sometimes central portion) becomes longitudinally straight. The distal half of the shaft may be slightly

concave laterally and convex medially. In cross-section, the

triangular shape presents an anterior, posterior, and medial

surface, as well as an anterior border, posterior border, and

interosseous border (each of which is located at the apex of

the triangular cross-sectional shape). The interosseous ligament is attached along the interosseous border apex of the

triangle, and there is no true lateral surface in this region of

the bone. More distally, the bone becomes progressively circular in cross-section. The shaft flares slightly distally as it

enlarges into the ulnar head.

The three borders of the ulnar shaft are the anterior,

posterior, and interosseous borders. The anterior border of

the ulna begins proximal at the prominent medial angle of

the coronoid process and extends distally along the

anteromedial aspect of the shaft to terminate anterior and

medial to the styloid process of the head of the ulna. The

anterior border is best defined in its proximal portion, and

becomes rounder, smoother, and less clearly defined in the

central distal portion as the shaft becomes progressively

circular in circumference distally. In this central portion of

the anterior border, the ulna provides a large surface origin for the flexor digitorum profundus muscle (see Fig.

1.17). The distal one-fourth of the anterior border is

referred to as the pronator ridge and provides origin for the

pronator quadratus (4).

The posterior border of the ulna begins proximally at the

apex of the triangular subcutaneous surface of the olecranon

(see Fig. 1.18). The posterior border extends distally along

the mid-posterior portion of the shaft, to terminate posterior to the styloid process. The posterior border is well

defined along its proximal one-third to three-fourths; however, as the ulna becomes more circular in cross-section distally, the distal portion of the posterior border is more

rounded, smooth, and poorly defined. In the well defined

proximal portion, the posterior border of the ulna gives rise

to the attachments of an aponeurosis, which provides a

common origin for the flexor carpi ulnaris, the extensor

carpi ulnaris, and the flexor digitorum profundus (see Fig.

1.18). The posterior border separates the medial and posterior surfaces of the ulna.

The interosseous border of the ulna is well defined and

can be somewhat sharp in its central portion (see Figs 1.17

to 1.20). The interosseous border actually extends along the

lateral margin of the ulna, beginning at the radial notch and

curving slightly anteriorly as it extends distally. A proximal

portion of the interosseous border is referred to as the

supinator crest, providing a ridge for the attachment of a

portion of the supinator muscle. In the distal one-fourth of

the shaft, the interosseous border is less well defined. The

interosseous ligament attaches along the interosseous border and is thickest at its attachment in the central portion

of the interosseous border. The interosseous ligament provides a partition that separates the anterior and posterior

surfaces of the ulna.

There are three surfaces of the shaft of the ulna: the anterior, posterior, and medial surfaces. The anterior surface of

the ulna lies between the interosseous border (located laterally) and the anterior border (located medially). The anterior surface is wide in its proximal portion and slightly concave along the proximal one-half or three-fourths of the

shaft. In this broad proximal portion, the surface is slightly

roughened and provides the large origin of the flexor digitorum profundus (see Fig. 1.17). The origin of the flexor

digitorum profundus extends to cover most of the anterior

surface, from the proximal third to the distal end of the

middle third. The distal fourth of the anterior surface is

covered by the pronator quadratus, which takes origin from

an oblique oval area (see Fig. 1.17). The nutrient canal

enters the ulna at the anterior surface at the junction of the

proximal and middle thirds. A branch of the anterior

interosseous artery enters at this site.

The posterior surface of the shaft of the ulna is the area

between the posterior border and the interosseous border

(see Figs. 1.18 and 1.20). This surface is somewhat laterally

located along the shaft and is broad proximally, where the

posterior edge is well defined. The middle portion of the

posterior surface is narrower, straight, and begins to loose

the definition of the posterior edge as the shaft becomes

progressively rounder in cross-section. In the distal third,

the posterior surface is round and flares slightly as the ulnar

head is formed. In the proximal portion, there is an

oblique line or ridge, which begins proximally at the dorsal end of the radial notch and continues distally (see Fig.

1.18). There is a triangular surface proximal to this ridge

that provides the insertion area for the anconeus muscle.

The proximal part of the ridge also provides a portion of

the origin area for the supinator. Along the mid-portion of

the posterior surface of the ulnar shaft, there is a central,

longitudinal ridge that is referred to as the perpendicular

line (4). This perpendicular line provides an attachment for

the extensor carpi ulnaris. The medial part is smooth, and

covered by the extensor carpi ulnaris. The lateral part is

wider and rougher, and provides the origin for the supinator, the abductor pollicis longus, the extensor pollicis

1 Skeletal Anatomy 33

longus, and the extensor indicis proprius. Also attaching in

the vicinity of the perpendicular line is an aponeurosis that

provides a common attachment for the extensor carpi

ulnaris, flexor carpi ulnaris, and flexor digitorum profundus (Fig. 1.18).

The medial surface of the shaft of the ulna is the area

between the posterior border and the medial border. The

medial surface is broad proximally and slightly concave in

its proximal two-thirds. As the shaft extends distally, the

medial surface becomes more narrow and round, and

slightly convex. The medial surface flares at the distal end to

form the head of the ulna. The proximal three-fourths of

the medial surface of the ulna provides a portion of the origin of the flexor digitorum profundus (Fig. 1.18).

Distal Ulna

The distal portion of the ulna consists of the head and styloid process (Fig. 1.22; see Figs. 1.17 to 1.20). The head of

the ulna is a rounded, partially spherical eminence that

forms from the flare of the distal shaft. The head is covered

in its distal and lateral surfaces with articular cartilage. Distally, it articulates with the proximal surface of the triangular fibrocartilage complex and ulnocarpal ligaments. The

lateral, anterior, and medial surfaces of the ulnar head articulate with the ulnar notch of the distal radius to form the

distal radioulnar joint.

The styloid process is a narrow, nonarticular prominence

based posterior and slightly medial to the ulnar head. The

styloid process extends distally to become the most distal

portion of the ulna. It provides attachment for the triangular fibrocartilage complex and ulnocarpal ligaments.

The tendon of the extensor carpi ulnaris passes through

a shallow groove located between the head and styloid

process on the posterior surface of the distal ulna.

Associated Joints

The ulna articulates by synovial joints with the humerus

and radius. The distal ulna also articulates with the carpus

through the ulnocarpal joint, a nonsynovial joint that is

capable of load transfer.

Proximally, the ulna articulates with the humerus

through the hinge-like ulnohumeral joint (see Fig.

1.21A–F). A proximal articulation also exists with the radial

head, the proximal radioulnar joint. The outer margin of

the radial head articulates with the radial notch of the ulna

(see Figs. 1.17 to 1.21).

Distally, the head of the ulna articulates with the radius

to form the distal radioulnar joint. This synovial joint normally does not communicate with the radial carpal joint.

Muscle Origins and Insertions

A variable number of muscles attach to the ulna, usually at

least 12 (see Figs. 1.17 and 1.18). The olecranon provides

attachment for the triceps insertion, anconeus insertion,

and origin of the ulnar head of the flexor carpi ulnaris

(medial aspect). The base of the coronoid process provides

the insertion area for the brachialis. The proximomedial

ulna also provides the attachment for a portion of the origin of the flexor digitorum superficialis and flexor digitorum profundus (whose origin extends into the shaft).

Medial to the insertion of the brachialis, the proximal shaft

or base of the coronoid process provides part of the origin

for the pronator teres. The proximolateral anterior ulna

provides the origin for the supinator. Occasionally, a small

portion of the origin of the flexor pollicis longus arises from

the proximal ulna (see Fig. 1.17). The dorsal shaft of the

ulna provides attachment for the common aponeurosis to

the extensor carpi ulnaris, flexor carpi ulnaris, and flexor

34 Systems Anatomy

FIGURE 1.22. Axial view of right distal radius and ulna, showing configuration of distal radioulnar joint, the carpal articular surface, and distal end of ulnar head and styloid process.

digitorum profundus, and the origin of the abductor pollicis longus, extensor pollicis longus, and extensor indices

(Fig. 1.18). On the anterior aspect of the shaft of the ulna,

the flexor digitorum profundus occupies a vast origin area,

covering the major portion of the anterior shaft. Distally,

the medial aspect of the anterior shaft provides the origin

for the pronator quadratus (Fig. 1.17).

Clinical Correlations: Ulna

Olecranon Osteotomy (Nonarticular Portion)

On the central portion of the articular surface of the proximal ulna, in the trochlear notch, there is an area in the joint

that is devoid of articular cartilage. In this area, the olecranon is slightly narrower. An olecranon osteotomy placed in

this area can avoid injury to the articular surface.

Fractures of the Olecranon

Several classification systems have been described for fractures of the olecranon (17,47a). A modification of the Colson classification recently has been popularized (48):

n Type I: fracture of the olecranon that is nondisplaced

n Type II: fracture of the olecranon that is displaced but

without elbow instability

n Type III: fracture of the olecranon that is comminuted,

but without elbow instability

n Type IV: fracture of the olecranon that is comminuted,

unstable, and with elbow instability

Fractures of the Coronoid

Fractures of the coronoid has been classified into three types

(49):

n Type I: fracture of the coronoid involving only the tip

n Type II: fracture of the coronoid involving one-half or

less of the coronoid

n Type III: fracture of the coronoid involving more than

one-half (50)

Nightstick Fracture

This is a single-bone forearm fracture involving the shaft of

the ulna, often nondisplaced or minimally displaced (51). It

was originally described from nightstick injury, when the

forearm is placed above the shoulder to protect the face or

body from blow from nightstick.

Monteggia Fracture

This fracture of the proximal third of the ulna and a concomitant anterior dislocation of the radial epiphysis was

described by Monteggia in 1814 (52). The classification has

been modified by Bado to include four subtypes (53):

n Type I: Anterior dislocation of the radial head with associated anteriorly angulated fracture of the ulna shaft

n Type II: Fracture of the ulnar diaphysis with posterior

angulation at the fracture site and a posterolateral dislocation of the radial head

n Type III: Fracture of the ulnar metaphysis with a lateral

or anterolateral dislocation of the radial head

n Type IV: Fracture of the proximal third of the radius and

ulna at the same level with an anterior dislocation of the

radial head

Fracture of the Ulnar Styloid and Implications

for Attached Ligaments

Because of the attachments of the triangular fibrocartilage

complex, fracture of the ulnar styloid may represent avulsion fracture or concomitant injury to the triangular cartilage complex.

Accessory Bones

Several accessory bones can be associated with the distal

ulna and may be mistaken for fractures. An accessory bone

usually represents the residual of a secondary ossification

center that does not fuse with the associated bone, but it

also may arise from trauma or from heterotopic ossification

of synovial tags (46,47). The accessory bones associated

with the distal ulna include the os triangulare (located distal to the distal end of the ulna, between the ulna, lunate

and triquetrum), the os ulnostyloideum (located in the

vicinity of the ulnar styloid), and the os pisiforme secundarium (located between the pisiform and distal ulna; see

Fig. 1.27B) (46) (see descriptions earlier, under Ossification

Centers and Accessory Bones). Disagreement exists as to the

origin of the os triangulare (25,46). It has been classified as

soft tissue calcification, an old avulsion fracture, or as arising from a secondary ossification center (from the ulna styloid). It has been reported to be present bilaterally without

preexisting history of trauma, which supports its existence

as a true independent ossicle (25). Schultz (25) has emphasized that differentiation of an accessory bone from a recent

or nonunited fracture of the ulna styloid may be difficult.

Differentiation from a fracture of the ulnar styloid may be

assisted by noting the length and completeness of the ulna

styloid. If the styloid process is of normal contour and no

defects are present indicating the location of an avulsed

fragment, the area of ossification probably represents an

accessory bone. At times, the ulna styloid may arise from a

separate center of ossification, and failure of fusion of this

center leads to disruption of the normal contour of the styloid. In a recent fracture, the fracture line is found dividing

1 Skeletal Anatomy 35

the ulna styloid without the presence of dense opposing surfaces. Comparative radiographs can assist in the diagnosis if

the condition is found to be bilateral.

Arthritis of the Distal Radioulnar Joint

Loss of congruity of the distal radioulnar joint can occur

from angulation or joint disruption in distal radius fractures

(Colles’ fracture), or from dislocation or subluxation from

Galeazzi-type fractures or fractures of the radial head with

concomitant injury to the interosseous ligament resulting

in proximal translation of the radius (Essex-Lopresti fracture).

Positive Ulnar Variance

Positive ulnar variance can be associated with shortening of

the radius either from congenital or traumatic causes. 

Positive variance can lead to increased force transmission

through the ulnocarpal joint or to impingement of the

ulnar head on the lunate or triquetrum. Operative management can consist of shortening of the ulna, distal ulna resection, or lengthening of the distal radius.

Negative Ulnar Variance

Negative ulnar variance is associated with Kienböck’s disease. In the absence of arthritic or degenerative changes,

management may consist of lengthening the ulna or shortening the radius to produce a neutral ulnar variance.

RADIUS

Derivation and Terminology

The radius derives its name from the Latin for spoke (i.e., of

a wheel) (1). The plural of radius is radii (1).

Ossification Centers

The radius contains three ossification centers: one for the

proximal portion, one for the shaft (body), and one for the

distal portion (Figs. 1.23 and 1.24). The ossification center

for the shaft first becomes visible in the mid-portion of the

bone at approximately the eighth week of fetal life. Ossification begins in the distal end during the second year of life.

Ossification of the proximal end becomes visible during the

fifth year. The proximal epiphysis fuses with the ossification

center of the shaft at 15 to 18 years of age. The distal epiphysis fuses to the shaft between the seventeenth and twentieth year. Occasionally, an additional center is visible in the

radial tuberosity, which appears at approximately the fourteenth or fifteenth year.

Accessory bones can be associated with the distal

radius. These include the os radiostyloideum and the os

radiale externum (parascaphoid) (see Fig. 1.27B) (25,46).

The os radiostyloideum usually is located at the lateral

aspect of the distal radius, in the vicinity of the radial styloid. The os radiale externum is located slightly distal to

the site of the os radiostyloideum, between the radial styloid and the scaphoid. An accessory bone, if present, usually is the result of a secondary or additional ossification

center that does not fuse with the associated bone. That

associated with the distal radius usually is from a secondary or additional ossification center of the radial styloid (46) (see Fig. 1.27B). Accessory bones also can occur

from other causes, such as trauma (46) or heterotopic ossification of synovial tags (47). Therefore, anomalous, irregular ossicles or ossicles of abnormal size or shape may be

encountered that do not fit a specific described accessory

bone or location.

36 Systems Anatomy

FIGURE 1.23. Schematic illustration of the radius, showing ossification centers. There are three centers: one for the proximal

portion, one for the body (shaft), and one for the distal portion.

Osteology of the Radius

The radius lies laterally in the forearm, has a long, narrow

shaft, and is widened proximally and distally to form the

head and styloid process, respectively. The radius consists of

three major parts: the proximal portion (proximal extremity), the shaft (body), and the distal portion (distal extremity). The radius lies parallel to and is slightly shorter than

the ulna (see Figs. 1.17 to 1.20). The proximal end is much

smaller than the distal portion. At the elbow, the radial head

articulates with the capitulum of the humerus and with the

radial notch of the proximal ulna. At the wrist, the distal

radius articulates with the scaphoid and lunate at the radiocarpal joint, and with the head of the ulna at the distal

radioulnar joint. The proximal and distal articulations with

the ulna provide forearm pronation and supination. The

distal end articulation at the radiocarpal joint provides wrist

extension, flexion, and radial and ulnar deviation. The

radiocarpal joint usually transfers most of the force from the

wrist to the radius, and subsequently to the elbow.

The internal structure of the radius is that of a long bone

with a long, narrow medullary cavity (see Figs. 1.17 to

1.20). The medullary canal is enclosed by thick cortical

bone, which is strongest and thickest along the interosseous

border. The cortex becomes thinner at the proximal and

distal ends of the radius. At the proximal end, the shaft

flares out to form the head, with a central, cup-shaped area

of the head containing relatively thick subchondral bone.

The trabeculae of the proximal and distal radius are

arranged into a somewhat arched pattern. Proximally, the

trabeculae pass proximally from the cortical layer of the

shaft to the fovea of the head of the radius. These trabeculae are crossed by transverse trabeculae that are oriented

parallel to the surface of the fovea. In a similar manner, the

trabeculae of the distal radius are arranged so that they

extend longitudinally from the cortical bone and course to

the articular surface. Additional trabeculae cross parallel to

the surface of the joint.

Proximal Radius

The proximal end of the radius consists of the head, neck,

and the tuberosity (see Figs. 1.17 to 1.20). The head is

shaped somewhat like a thick disc or short cylinder. The

proximal surface forms a shallow cup, the central portion of

which is the fovea. The fovea of the radial head articulates

with the capitulum of the distal humerus. The articular

margin or periphery of the head is smooth and approximately 5 to 10 mm high. The radial head is thickest in the

medial portion where it articulates with the radial notch of

the ulna. The radial head is slightly shorter in the lateral

portions, where it is surrounded by the annular ligament.

The head is connected to the smooth, narrower radial neck.

The neck is cylindrical and has a thick cortex. The head

overhangs the neck, giving a slight mushroom-like appearance. On the posterior aspect of the neck there is a slight

ridge or roughened surface for the insertion of a portion of

the proximal supinator. The anterior surface of the neck is

smooth. Along the anterior undersurface of the rim formed

by the junction of the radial head and radial neck there are

several small nutrient foramina. The tuberosity of the radius

lies on the anteromedial aspect of the proximal radius, distal to the neck. The tuberosity is rough on its most medial

and posterior aspects for the insertion of the biceps tendon.

On its most anterior aspect, the tuberosity is smooth, in

which a bursa is interposed between the tendon and the

radius.

1 Skeletal Anatomy 37

FIGURE 1.24. Proximal and distal radius in a young

adult, showing epiphyseal lines.

Shaft of the Radius

The shaft of the radius, often referred to in anatomic textbooks as the body, consists of the major portion of the bone

between the head and the distal end (2,4,5). In the proximal portion, the shaft is round or cylindrical where it joins

the radial neck. More distally, the shaft becomes triangular

in cross-section, with an apex directed toward the ulna

where the interosseous ligament attaches. The triangular

cross-sectional area of the shaft results in three surfaces

(anterior, posterior, and lateral) separated by three borders

(anterior, posterior, and interosseous). The interosseous

border along the medial aspect is sharp along its margin,

except proximally near the tuberosity. The shaft gradually

increases in size from proximal to distal. The shaft of the

radius is gently curved, convex dorsally and laterally. The

anterior (palmar, volar) surface is correspondingly gently

curved concave volarly. The interosseous border, on the

medial aspect, is gently curved concave ulnarly.

The anterior border is located on the anterolateral surface of the shaft. It separates the anterior and lateral surfaces. It is well defined in its proximal and distal portions,

but poorly defined in its central or middle portion, where

the border is more rounded and less distinct. The anterior

border starts proximally from the distal portion of the

tuberosity and extends longitudinally to reach the anterior

part of the base of the styloid process. The proximal third

of the anterior border of the radius is elevated to form a

slight ridge known as the anterior oblique line of the radius.

The anterior oblique line is sharper and more defined in its

distal portion, forming a palpable crest along the lateral

margin of the anterior surface. The anterior oblique line

provides the area of origin of the flexor digitorum superficialis and flexor pollicis longus muscles. Proximal and lateral to the anterior oblique line, the area on the radius provides a portion of the insertion of the supinator muscle. In

the distal part of the shaft of the radius, along the distal

one-fourth, the anterior border is more clearly defined than

the central portion. This part of the anterior border provides the insertion area of the pronator quadratus and

attachment of the dorsal carpal ligaments. The distal portion of the anterior border continues distally and slightly

laterally, and terminates in a small tubercle on the anterolateral surface. This tubercle, located at the base of the styloid process, provides the insertion attachment for the brachioradialis muscle (Fig. 1.17).

The posterior border begins proximally at the posterior

aspect of the neck of the radius and extends distally to the

posterior aspect of the base of the styloid process. The posterior border separates the posterior surface of the radius

from the lateral surface. The border actually is rounded and

not clearly defined, especially in the most proximal and distal aspects. It is best defined in its middle third, where it is

slightly roughened.

The interosseous border extends along the medial aspect

of the radius in proximity to the ulna. Proximally, the

interosseous border is poorly defined. Distal to the radial

tuberosity, the interosseous border changes from a rounded

contour to a sharp, somewhat rough, prominent edge. The

edge is the most prominent and thickest at the junction of

the proximal third and distal two-thirds. A the distal portion of the interosseous border, approximately 5 cm from

the distal end of the radius, the interosseous border divides

into two ridges that continue to form the anterior and posterior margins of the ulnar notch. This creates a triangular

surface between the ridges, known as the medial surface of

the distal radius (5). This triangular area serves as an insertional area for a portion of the pronator quadratus. In this

distal area, the divided interosseous border separates the

anterior surface of the radius from the posterior surface.

Along its sharp distal three-fourths, the interosseous border

provides the attachment for the interosseous ligament, connecting the radius to the ulna.

The anterior surface of the shaft of the radius lies

between the anterior and interosseous borders. The surface

is concave in its proximal three-fourths, but becomes

slightly broader and flatter in its distal fourth. The large

concave proximal surface provides the origin for the flexor

pollicis longus. The muscle covers the major surface area of

the anterior surface. The flatter, broader distal portion of

the anterior surface is covered by the pronator quadratus.

Distal and radial to the attachment of the pronator quadratus, in the palmar aspect of the radial styloid, there is a triangular area separated from the shaft by a slight ridge. This

triangular area is roughened and provides attachment for

the radiocarpal ligaments. Several nutrient foramina are

present on the distal anterior surface of the radial metaphysis. Near the midpoint or in the vicinity of the junction of

the proximal and middle thirds of the anterior surface, there

usually is a nutrient foramen and canal. The foramen

receives a branch from the anterior interosseous artery. The

nutrient vessel enters the radius with a somewhat proximally directed course.

The posterior surface of the radius lies between the posterior and interosseous borders. It is flat, slightly convex, or

slightly rounded along most of its course. In the proximal

third, it is smooth and may be slightly concave, providing

for the attachment of the supinator, which covers the posterolateral surface of the proximal radius. Just distal to the

attachment of the supinator is the oblique insertion area of

the pronator teres, which extends to the lateral surface. In

the middle third of the posterior surface, the surface is

broad and may become slightly concave, providing origin

for the abductor pollicis longus and extensor pollicis brevis.

In the distal third of the posterior surface of the radius, the

surface is broad, convex, irregular, and grooved, providing

the passage and routing of the dorsal extensor tendon compartments (see later, under Distal Radius) (Fig. 1.18).

38 Systems Anatomy

The lateral surface of the radius is a gently convex surface lying between the anterior and posterior borders. It

generally is smooth, rounded, and remains convex along its

entire surface. In the proximal portion, it provides a portion

of the attachment of the supinator muscle. In the central

portion there is a slightly roughened oval area for the insertion of the tendon of the pronator teres. In the distal portion of the lateral surface, the surface is smooth where the

tendons of the abductor pollicis longus and extensor pollicis brevis muscles cross.

Distal Radius

The distal portion of the radius includes the metaphyseal

and epiphyseal regions. This portion of the radius is quadrilateral in cross-section and encompasses the widest portion

of the radius. Anatomic features include the anterior, posterior, medial, and lateral surfaces; the styloid process; the

dorsal (Lister’s) tubercle; the ulnar notch; and the radiocarpal and distal radioulnar joint articular surfaces.

The lateral surface flares out gradually from the shaft,

extending further along the lateral margin to form the styloid process. The styloid process is conical. A rough area at

the base of the styloid provides the attachment for the brachioradialis. This lateral surface is slightly rough, and projects distally to terminate in the tip of the styloid. The distal area of the styloid provides attachment for the articular

capsule and the capsular thickening of the collateral ligament. On the lateral surface of the radial styloid, there is a

flat groove for the passage the abductor pollicis longus and

extensor pollicis brevis tendons. The process is easily palpable and serves as a useful anatomic landmark to mark the

lateral margin of the radiocarpal joint.

The anterior surface of the distal radius is concave, palmarly directed, and widened or flared out from the contour

of the shaft. The surface is rough for the attachment of the

palmar radiocarpal ligaments, and multiple small foramina

are present to provide vascularity to this metaphyseal area of

the radius. The anterior surface has a thick, prominent

ridge, which is palpable approximately 2 cm proximal to

the thenar eminence. A portion of the anterior surface is

covered by the pronator quadratus, of which there are

attachments that extend distally to the area adjacent to the

area of the attachment of the wrist capsule and radiocarpal

ligaments.

The medial surface of the distal radius consists of the

ulnar notch and the articular surface for the ulnar head,

comprising the radial component of the distal radioulnar

joint. The ulnar notch is narrow, smooth, concave in the

anteroposterior plane, and roughly triangular, with the

widest portion distally. The margins of the articular surface

are bordered by a slight ridge, further defining the ulnar

notch. Small nutrient foramina are present just proximal to

the articular margin of the distal radioulnar joint.

The posterior (dorsal) surface of the distal radius flares

out gradually from the shaft. It is irregular, rough, convex,

and contains multiple small vascular foramina for the distal

radial metaphysis. In the mid-portion of the posterior distal

radius is the prominent dorsal (Lister’s) tubercle. It lies from

5 to 10 mm from the distal joint surface. A portion of the

extensor retinaculum attaches to Lister’s tubercle. On the

medial aspect of the dorsal tubercle is a deep, smooth

groove for passage of the extensor pollicis longus tendon.

On the most lateral aspect of the posterior distal radius,

there are less defined grooves, from lateral to medial, for

passage of the abductor pollicis longus, extensor pollicis

brevis, extensor carpi radialis longus, and extensor carpi

radialis brevis, respectively. The groove that contains the

extensor carpi radialis longus and brevis is broad and shallow, and subdivided into two parts by a slight ridge to allow

passage of each of the two tendons, with the longus located

lateral to the brevis.

On the ulnar aspect of the posterior distal radius, ulnar

to Lister’s tubercle, are faint grooves for passage of the

extensor indicis and extensor digitorum communis. The

extensor indicis tends to pass slightly deeper than the extensor digitorum communis. In this vicinity, along the dorsal

margin of the distal radius and adjacent to the cortex, the

posterior interosseous nerve courses.

The distal margin of the posterior surface of the distal

radius is rough to provide for the attachment of the dorsal

radiocarpal ligaments.

The carpal articular surface of the distal radius is roughly

triangular (apex lateral), smooth, concave, and curving and

extending distally along the lateral margin. The base of the

triangle intersects the articular surface of the distal radioulnar joint. On the carpal articular surface, there is a slight

division by a mild anteroposterior ridge. This divides the

articular surface into lateral and medial parts. The lateral

part is triangular and contains the scaphoid fossa. The

medial portion is more quadrangular and contains the

lunate fossa. The distal radiocarpal articular surface is concave and slightly oval, elongated from anterior to posterior.

Between the distal radioulnar joint and the radiocarpal joint

there is a slight separation of the articular surfaces by a

prominent ridge. This ridge, located in the ulnar notch,

provides the radial attachment for the triangular fibrocartilage.

Associated Joints

At the proximal end, the head of the radius articulates with

the capitulum of the humerus and with the radial notch of

the ulna (see Fig. 1.21B–F). At the distal end, the radius

articulates, through its ulnar notch, with the head of the

ulna to form the distal radioulnar articulation. Also at the

distal end, the radius articulates with the scaphoid and the

lunate at the radiocarpal joint. The scaphoid articulates

1 Skeletal Anatomy 39

with the scaphoid fossa of the distal radius. The specific

articulation with the scaphoid is referred to as the

radioscaphoid joint or, depending on the specific location in

the radioscaphoid joint, the articulation can be referred to

as the styloscaphoid joint [descriptive because of its significance for arthritis and the scapholunate advanced collapse

(SLAC) wrist]. The specific articulation with the lunate is

referred to as the radiolunate joint. The lunate articulates

with the lunate fossa of the distal radius. The interosseous

ligament between the radius and the ulna can be considered

a nonsynovial articulation.

Muscle Origins and Insertions

There usually are nine muscles that attach to the radius (see

Figs. 1.17 and 1.18). The biceps insertion attaches to the

radial tuberosity. The supinator originates from the oblique

ridge of the proximal medial aspect. The flexor digitorum

superficialis originates along an oblique line on the anterior

proximal and central diaphysis. The flexor pollicis longus

origin covers the anterior shaft of the radius. The insertion

of the pronator quadratus attaches to the distal anterior diaphysis and metaphysis. The midshaft on the radial aspect

provides the insertion of the pronator teres. The origins of

the abductor pollicis longus and extensor pollicis longus

attach to the posterior midshaft. The brachioradialis inserts

into the lateral aspect of the distal radius, just distal to the

styloid.

Clinical Correlations: Radius

The Oblong Shape of the Scaphoid Fossa

The oblong shape of the scaphoid fossa of the distal radius

influences radioscaphoid arthritis, as can be demonstrated

with the SLAC wrist from scapholunate instability. The

scaphoid fossa of the radius is somewhat oblong in shape,

and accepts the oblong articular surface of scaphoid. The

lunate fossa of the radius is more nearly spherical, and

accepts the more hemispherical articular surface of the

lunate. With scapholunate instability, mobility of the

scaphoid in the oblong fossa is not as well tolerated because

areas of stress concentration result if the scaphoid rotates

abnormally. The more spherical shape of the radiolunate

articulation can tolerate motion of the lunate more easily,

without stress concentration. Therefore, in long-standing

scapholunate instability, arthritic changes usually develop

first in the radioscaphoid joint (styloscaphoid joint),

whereas the radiolunate joint may be relatively well preserved until the latest stages (54–60).

Essex-Lopresti Lesion

Fracture of the radial head (which results in the loss of proximal support of the radius) along with injury to the

interosseous ligament between the radius and ulna may

allow proximal migration of the radius. This injury was

described by Essex-Lopresti in 1951 (61,62). At the wrist,

the proximal migration of the radius results in relative

shortening of the radius, producing a relative positive ulnar

variance. Management in the acute setting includes reconstruction or metallic prosthetic replacement of the radial

head (to regain proximal support), and, as needed, pinning

of the distal radius and ulna to hold the reduced distal

radioulnar joint accurately.

Galeazzi’s Fracture

Fracture of the distal radial shaft with an associated dislocation or subluxation of the distal radioulnar joint was

described by Galeazzi in 1934 (63–65). The fracture usually

occurs at the junction of the middle and distal thirds of the

radius, and usually has a transverse or short oblique configuration. Open reduction with internal fixation (ORIF) usually is the preferred method of treatment (65).

Fracture Classification of the Radial Head

Fractures of the radial head have been described by Mason

in 1954 (65a), and recently modified by Hotchkiss. The

Hotchkiss classification is as follows (62):

n Type I: Nondisplaced or minimally displaced fracture of

the radial head or neck. Forearm rotation is limited only

by acute pain and swelling. Intraarticular displacement

of the fracture is less than 2 mm. Treatment usually is

sling immobilization and active motion as early as tolerated.

n Type II: Displaced (>2 mm) fracture of the head or neck,

motion may be mechanically limited or incongruous,

without severe comminution (repairable by ORIF), and

fracture involves more than a marginal lip of the radial

head. Treatment is variable, and includes either ORIF

(recently more popular), early motion without excision,

or excision.

n Type III: Severely comminuted fracture of the radial

head and neck, not reconstructible, and requires excision

for movement. Treatment usually is excision, with possible prosthetic replacement to improve valgus stability

and prevent proximal translation of the radius.

Colles’ Fracture

Colles described this fracture of the distal radius in 1814

(66). The fracture involves the distal metaphysis, which is

dorsally displaced and angulated, and usually occurs within

2 cm of the articular surface. The fracture may extend into

the distal radiocarpal joint. Classic features include dorsal

angulation (silver fork deformity), dorsal displacement,

radial angulation (loss of radial inclination), and radial

40 Systems Anatomy

shortening. There often is accompanying fracture of the

ulnar styloid, which may signify avulsion of the triangular

fibrocartilage complex (67).

Barton’s Fracture

Barton described this fracture of the distal radius in 1838

(68). The fracture is a fracture–dislocation in which the rim

of the distal radius, dorsally or palmarly, is displaced with

the hand and carpus (68,69). The fracture differs from the

Colles’ or Smith’s fracture in that the dislocation is the most

clinically and radiographically obvious abnormality, with

the radial fracture noted secondarily. The volar Barton’s

fracture is similar to the Smith’s type III fracture, where

both involve palmar dislocation of the carpus associated

with an intraarticular distal radius component.

Smith’s Fracture

Smith described an additional fracture pattern of the distal radius in 1854. In this fracture, often called reverse

Colles’ fractures, the distal radial fragment is palmarly

angulated or displaced, producing a “garden spade” deformity (69,70). The hand and wrist are displaced forward or

palmarly with respect to the forearm. The fracture may be

extraarticular, intraarticular, or part of a fracture–dislocation (67,70,71). The classification modified by Thomas

includes type I, which is extraarticular; type II, which

crosses into the dorsal articular surface; and type III,

which is intraarticular and similar to the volar Barton’s

fracture–dislocation.

Chauffeur’s Fracture

This fracture of the radial styloid was described originally

because of the mechanism of injury, whereby the hand crank

of early automobiles would backspin to strike the wrist. The

fracture, if displaced, is treated with ORIF. If the fracture is

displaced more than 3 mm, there may be an associated

scapholunate dissociation, which may benefit from repair of

the ligament as well as ORIF of the styloid (67,72).

Accessory Bones

Accessory bones, the os radiostyloideum and the os radiale

externum, are located in the vicinity of the radial styloid

(25,46) (see Fig. 1.27B). The os radiale externum is located

slightly distal to the site of the os radiostyloideum. If present, these accessory bones can be mistaken for a fracture.

An accessory bone usually represents the residual of a secondary ossification center that does not fuse with the associated bone, but it also may arise from trauma or from heterotopic ossification of synovial tags (46,47) (see

description earlier, under Ossification Centers and Accessory Bones).

CARPUS

General Aspects

The carpus consists of eight carpal bones, arranged in a

proximal and a distal row, each row containing four bones.

The proximal row includes (from lateral to medial) the

scaphoid, lunate, triquetrum, and pisiform. The pisiform is

located palmar to the plane of the remaining three carpal

bones of the proximal row, and the pisotriquetral joint is

separated from the joining articulations. The distal row

includes (from lateral to medial) the trapezium, trapezoid,

capitate, and hamate (Figs. 1.25 and 1.26).

The proximal row is convex proximally and concave distally. The proximal row articulates proximally with the distal radius and with the triangular fibrocartilage complex,

forming the radiocarpal and ulnocarpal joint. The proximal

row articulates distally with the distal carpal row, forming

the midcarpal joint.

1 Skeletal Anatomy 41

FIGURE 1.25. Skeletal hand and wrist, palmar aspect.

The four bones of the distal row articulate distally with

the five metacarpal bones and with each other. The bones of

the distal carpal row are straighter in alignment across the

wrist than the proximal row, especially at their distal articulations with the metacarpal bones.

On the dorsal surface of the carpus, a gentle convex

arch is formed by the arrangement of the proximal and

distal rows. On the palmar surface, however, a deep concavity if formed, designated the carpal groove. The carpal

groove is accentuated by the palmar projection of the pisiform and hook of the hamate medially, and by the projection of the scaphoid tuberosity and trapezial ridge laterally.

The midcarpal joint and the radiocarpal joint usually do

not communicate with each other; if communication does

occur, as seen through flow of dye from an arthrogram,

there is either a tear or incompetence of the scapholunate or

lunotriquetral ligaments.

The vascular supply to the carpus is through two main

systems, the dorsal carpal vascular system and the palmar

carpal vascular system (73) (see Fig. 1.29). The dorsal and

palmar systems consist of a series of dorsal and palmar

transverse arches that are connected by anastomoses formed

by the radial, ulnar, and anterior interosseous arteries. The

specific vascular patterns in each carpal bone (intraosseous

vascularity) are described in the section on osseous anatomy

(73).

The ossification of the carpus may be quite variable (5)

(see Fig. 1.26). The carpal bones usually are cartilaginous at

birth, with the exception of the capitate and the hamate,

where ossification already may be present. Each carpal bone

ossifies from one center; the capitate usually is first and the

pisiform usually last, but variability may exist in the order

of ossification of the other carpal bones (74–76) (Fig. 1.27).

The specifics of ossification of each carpal bone are discussed separately later.

The carpus can be associated with several accessory

ossicles (46) (see Fig. 1.27B; Table 1.2). In general, the

development of these accessory bones is from an additional or anomalous secondary ossification center, and

therefor the accessory bones are described later under sections on ossification. Accessory bones however, also can

occur from other causes such as trauma (46) or heterotopic ossification of synovial tags (47). Anomalous, irregular ossicles or ossicles of abnormal size or shape thus may

be encountered that do not fit a specific described accessory bone or location.

In addition to accessory bones, congenital fusions (or

coalitions) have been noted to occur in most of the carpal

articulations (see Fig. 1.27C). Congenital coalitions are

thought to occur either by the fusion of two ossification

centers or by the nonseparation of two cartilage elements,

resulting in one bone (46,77).

SCAPHOID

Derivation and Terminology

The scaphoid (os scaphoideum, os naviculare manus, carpal

navicular) derives its name from the Greek skaphe, which

means “skiff” or “light boat.” Scaphoid therefore denotes

“boat-shaped” (1). The word navicular is derived from the

Latin navicula, also indicating a boat.

Ossification Centers and Accessory Bones

The scaphoid usually has one ossification center (see Fig.

1.27A). It begins to ossify in the fourth year in girls, and the

fifth year in boys (74). Occasionally, an additional ossification center fails to unite, forming an accessory ossicle, the

os centrale (centrale dorsale, episcaphoid). The os centrale

42 Systems Anatomy

FIGURE 1.26. Skeletal hand and wrist, dorsal aspect.

FIGURE 1.27. A: Schematic illustrations showing

times of ossification of the carpus and hand. B:

Accessory ossicles of the wrist: schematic illustration of the carpus showing the various accessory

bones and approximate locations. C: Possible

sites for carpal coalitions. (B and C after O’Rahilly

R. Developmental deviations in the carpus and

A the tarsus. Clin Orthop 10:9–18, 1957.)

B C

occurs between the scaphoid, trapezoid, and capitate bones

(see Fig. 1.27B). During the second prenatal month, it is a

cartilaginous nodule usually fusing with the scaphoid.

Besides the os centrale, an additional ossification center

may give rise to two large portions of the scaphoid. If these

fail to fuse, the result is a bipartite scaphoid (25). Bipartite

scaphoids are rare, usually bilateral, and can be distinguished from a fracture by the smooth cortical edges, lack

of history of trauma, and absence of displacement or degenerative changes (25).

Several other accessory bones can be associated with

the scaphoid. These accessory bones, if present, usually

are the result of secondary or additional ossification centers that do not fuse with the scaphoid. These include the

os centrale, the os radiale externum (os parascaphoid),

the os epitrapezium, os epilunatum (os centrale II), and

the os radiostyloideum (see Fig. 1.27B) (25,46). The os

centrale is located between the scaphoid, capitate, and

trapezoid. The os radiale externum is located at the distal

lateral margin of the scaphoid tubercle, adjacent to the

trapezium. The os epitrapezium is located just distal to

the site of the os radiale externum at the distal lateral

aspect of the scaphoid in close proximity to the trapezium. The os epilunatum is located in the region between

the scaphoid and lunate, at the more distal aspect of the

scapholunate articulation. The os radiostyloideum is

located in the vicinity of the radial styloid, slightly proximal to the lateral mid-portion of the scaphoid (46) (see

Fig. 1.27B).

Osteology of the Scaphoid

The scaphoid is the largest bone of the proximal carpal

row, located proximally and radially (Fig. 1.28; see Figs.

1.25, 1.26, 1.37, and 1.38). It consists internally of cancellous bone, surrounded by a cortical shell (see Fig. 1.28).

The cortex of the distal pole (tuberosity) is relatively

thick. The axis of the scaphoid is directed distally, laterally,

and palmarly. It rests in a plane at approximately 45

degrees to the longitudinal axis of the wrist (67). Articular

cartilage covers 80% of the surface (67). The major portions include the tuberosity (located palmarly and distally), the body, and the proximal pole. The central narrow

portion of the body is the waist. The palpable scaphoid

tuberosity is located at the base of the thenar eminence

and usually is in line with the radial border of the long finger. The tuberosity extends palmarly, and is more readily

palpable with the dorsiflexed wrist in radial deviation

(which increases the palmar flexion of the scaphoid and

thus directs the tuberosity into the palm, where is

becomes easily palpable). When the wrist is ulnarly deviated, the palmar flexion of the scaphoid decreases, and

thus the tuberosity is more difficult to palpate. The dorsal

surface is rough, grooved, and narrower than the palmar

44 Systems Anatomy

TABLE 1.2. ACCESSORY BONES OF THE WRIST

Os capitatum secundarium (carpometacarpale V)

Os centrale (centrale dorsale, episcaphoid)

Os epilunatum (centrale II)

Os epitrapezium

Os epitrapezoideum (trapezoideum dorsale)

Os epitriquetrum (epipyramis, centrale IV)

Os gruberi (carpometacarpale VI)

Os hamulare basale (carpometacarpale VII)

Os hamuli proprium

Os hypolunatum (centrale III)

Os hypotriquetrum

Os metastyloideum

Os parastyloideum (carpometacarpale III)

Os paratrapezium

Os pisiforme secundarium (ulnare antebrachii, metapisoid)

Os praetrapezium (carpometacarpale I)

Os radiale externum (parascaphoid)

Os radiostyloideum

Os styloideum (carpometacarpale IV)

Os subcapitatum

Os trapezium secundarium (multangulum majus secundarium,

carpometacarpale II)

Os trapezoideum secundarium (multangulum minus

secundarium)

Os triangulare (intermedium antebrachii, triquetrum

secundarium)

Os ulnare externum

Os ulnostyloideum

Os vesalianum manus (vesalii, carpometacarpale VIII)

From O’Rahilly (44–46).

FIGURE 1.28. Right scaphoid. A: Dorsal aspect. B: Palmar aspect.

A B

surface. A dorsal groove courses the entire length of the

scaphoid, and provides for the attachment of ligaments

and vessels. The rough dorsal area in the region of the

waist contains small vascular foramina, more of which

usually are located slightly distally (78). These foramina

allow entrance of the vital dorsal ridge vessels, a leash of

vessels that supply vascularity to the body and, through

retrograde flow, to the proximal pole (73,79). The lateral

surface, directed proximally and radially, is convex and

covered with articular cartilage. The most medial surface,

which articulates with the lunate (lunate surface), is

located ulnarly, has a flat, semilunar shape, and contains a

relatively small surface area for lunate articulation. It is

covered with articular cartilage. The portion articulating

with the capitate is large, concave, and faces distomedially,

and is covered with articular cartilage. The most distal

portion articulates with the trapezium and trapezoid. This

distal portion is a continuous, slightly convex surface.

This distal articulation usually has two parts or “facets,”

separated by a small ridge. The presence and morphology

of the articular facets is variable; in approximately 25% of

specimens, there may be a palpable but not readily visually

identifiable separation of the facets, and the two facets

may not be distinguishable at all in approximately 19%

(see below, Anomalies and Variations). Two distinct facets

are present in at least 82% of specimens. The medial facet

articulates with the trapezoid, and the lateral facet articulates with the trapezium. Each facet is covered with articular cartilage. The articular surfaces of the proximal portion of the scaphoid (including those articulating with the

capitate, lunate, and distal radius) are all covered with

articular cartilage, and thus do not provide any soft tissue

attachments for vascularity. Hence, the vascular supply to

the proximal pole is from retrograde flow from the dorsal

ridge vessels located at the level of the waist.

Anomalies and Variations in Morphology

of the Scaphoid

There is anatomic variability in the morphology of the distal articular surface of the scaphoid that articulates with the

trapezium and trapezoid. The joint may or may not contain two distinct facets. Viegas and coworkers have shown

that in 81.2% of scaphoids studied, there was a distinctly

separate facet for the trapezoid articulation and another

distinct facet for the trapezium, with an interfacet ridge

separating the two. The interfacet ridge was both visible

and palpable in 56.4% of wrists. In 24.8% of wrists, the

scaphoid was found to have a palpable, but not readily visually identifiable interfacet ridge. In the remaining 18.8% of

wrists, the scaphoid had a smooth distal articular surface

without a visually or palpably identifiable ridge between the

area of trapezial or trapezoidal articulation on the scaphoid

(80,81).

Vascularity of the Scaphoid

The scaphoid receives its vascular supply mainly from the

radial artery. Vessels enter in the limited areas dorsally and

palmarly that are nonarticular areas of ligamentous attachment (79,82–84) (Fig. 1.29).

The dorsal vascular supply to the scaphoid accounts for

70% to 80% of the internal vascularity of the bone, all in

the proximal region (79) (see Fig. 1.29A). On the dorsum

of the scaphoid, there is an oblique ridge that lies between

the articular surfaces of the radius and of the trapezium and

trapezoid. The major dorsal vessels to the scaphoid enter the

bone through small foramina located on this dorsal ridge

(79,82,84,85). The dorsal ridge is in the region of the

scaphoid waist. At the level of the intercarpal joint, the

radial artery gives off the intercarpal artery, which immediately divides into two branches. One branch runs transverse

to the dorsum of the wrist. The other branch runs vertically

and distally over the index metacarpal. Approximately 5

mm proximal to the origin of the intercarpal vessel at the

level of the styloid process of the radius, another vessel is

given off that runs over the radiocarpal ligament to enter

the scaphoid through its waist along the dorsal ridge. In

70% of specimens, the dorsal vessel arises directly from the

radial artery. In 23%, the dorsal branch has its origin from

the common stem of the intercarpal artery. In 7%, the

scaphoid receives its dorsal blood supply directly from the

branches of both the intercarpal artery and the radial artery.

There are consistent major communications between the

dorsal scaphoid branch of the radial artery and the dorsal

branch of the anterior interosseous artery. No vessels enter

the proximal dorsal region of the scaphoid through the dorsal scapholunate ligament, and no vessels enter through

dorsal cartilaginous areas.

The dorsal vessels usually enter the scaphoid through

foramina located on the dorsal ridge at the level of the

scaphoid waist. However, in a few of the studied specimens,

the vessels enter just proximal or distal to the waist. The

dorsal vessels usually divide into two or three branches soon

after entering the scaphoid. These branches run palmarly

and proximally, dividing into smaller branches to supply

the proximal pole as far as the subchondral region.

The palmar vascular supply accounts for 20% to 30% of

the internal vascularity, all in the region of the distal pole

(79,85) (see Fig. 1.29B). At the level of the radioscaphoid

joint, the radial artery gives off the superficial palmar

branch. Just distal to the origin of the superficial palmar

branch, several smaller branches course obliquely and distally over the palmar aspect of the scaphoid to enter

through the region of the tubercle (79,83). These branches,

the palmar scaphoid branches, divide into several smaller

branches just before penetrating the bone. In 75% of specimens, these arteries arise directly from the radial artery

(79). In the remainder, they arise from the superficial palmar branch of the radial artery. Consistent anastomoses

1 Skeletal Anatomy 45

exist between the palmar division of the anterior

interosseous artery and the palmar scaphoid branch of the

radial artery, when the latter arises from the superficial palmar branch of the radial artery. There are no direct communicating branches between the ulnar artery and the palmar branches of the radial artery that supply the scaphoid.

Vessels in the palmar scapholunate ligament do not penetrate the scaphoid. The palmar vessels enter the tubercle

and divide into several smaller branches to supply the distal

20% to 30% of the scaphoid. There are no apparent anastomoses between the palmar and dorsal vessels (79).

Associated Joints

The scaphoid articulates with five bones: the radius proximally, the lunate medially, the capitate medially and distally,

and the trapezoid and trapezium distally (see Figs. 1.25,

1.26, 1.28, 1.37, and 1.38). The proximal lateral portion of

the scaphoid sits in the scaphoid fossa of the radius, forming

the radioscaphoid joint. In the distal portion of the

radioscaphoid joint, where the mid-lateral portion of

scaphoid articulates with the radial styloid, the specific portion of the joint can be referred to as the styloscaphoid joint

(descriptive because of its significance for arthritis and SLAC

wrist). The articulation with the lunate, forming the

scapholunate joint, has a relatively small surface area, in part

because of the narrow crescent shape of the lunate, which

may contribute to the difficulty in performing arthrodesis of

this joint. The scaphocapitate articulation has a relatively

large surface area, usually allowing successful arthrodesis of

this joint. The distal articulation of the scaphoid with the

trapezoid and trapezium is referred to as the triscaphe joint.

46 Systems Anatomy

FIGURE 1.29. A: Classic depiction of dorsal pericarpal arterial network.

A

1 Skeletal Anatomy 47

FIGURE 1.29. (continued) B: Classic depiction of palmar pericarpal arterial network. (A and B

after Taleisnik J. The vascular anatomy of the wrist. In: Taleisnik J, ed. The wrist. New York:

Churchill Livingstone, 1985:51–78.) AIA, anterior interosseous artery; DMCA, dorsal metacarpal

artery; PF, perforating branches; PMA, palmar metacarpal artery; CPDA, common palmar digital

artery; PDA, proper palmar digital artery.

(continued on next page)

B

48 Systems Anatomy

FIGURE 1.29. (continued) C: Drawing of the arterial supply of the lateral aspect of the wrist.

D: Schematic drawing of the dorsum of the wrist, showing vascular contributions to the carpal

bones.

C

D

Muscle Origins and Insertions

A small portion of the abductor pollicis brevis may originate from the palmar surface of the scaphoid tuberosity.

(The major portion of origin of the abductor pollicis brevis

usually is from the proximal part of the palmar surface of

the trapezium.) A portion of the transverse carpal ligament

also attaches to the medial portion of the scaphoid tuberosity (see Fig. 1.37).

Clinical Correlations: Scaphoid

The scaphoid is the most commonly fractured bone of the

carpus (86). It is susceptible to fractures at any level

[approximately 65% occur at the waist, 15% through the

proximal pole, 10% through the distal body, 8% through

the tuberosity, and 2% in the distal articular surface (67)].

Scaphoid fractures have a relatively high incidence of

nonunion (8% to 10%), frequent malunion, and late

sequelae of carpal instability and posttraumatic arthritis

(67).

The relatively small surface area of the scapholunate

joint (due in part to the narrow crescent shape of the

lunate) probably contributes to the difficulty in achieving

operative arthrodesis of this joint. While, the relatively large

surface area of the scaphocapitate joint facilitates successful

operative arthrodesis.

Arthrodesis of the triscaphe joint stabilizes or “anchors”

the distal portion of the scaphoid, and thus prevents collapse into palmar flexion, as is seen when there is disruption

of the scapholunate ligaments. Therefore, triscaphe

arthrodesis has been described for treatment of scapholunate instability.

The retrograde vascularity of the scaphoid enters the

dorsal waist through the dorsal ridge vessels (73,79), and

these vessels should be protected during dorsal exposure of

the scaphoid. Avascular necrosis of the proximal pole of the

scaphoid is due to disruption of the retrograde vessels that

supply the proximal pole. Preiser’s disease describes avascular necrosis of the scaphoid, usually occurring in the proximal pole (87,88).

Accessory Bones

Several accessory bones can be associated with the scaphoid

and may be mistaken for fractures. An accessory bone usually represents the residual of a secondary ossification center that does not fuse with the associated bone, but it also

may arise from trauma or from heterotopic ossification of

synovial tags (46,47). The accessory bones associated with

the scaphoid include the os centrale (located between the

scaphoid, capitate, and trapezoid), the os radiale externum

(located at the distal radial border of the scaphoid tuberosity), the os epitrapezium (located between the scaphoid and

1 Skeletal Anatomy 49

FIGURE 1.29. (continued) E: Schematic

drawing of the palmar aspect of the wrist,

showing the vascular contributions to the

carpal bones. (C–E after Gelberman RH,

Panagis JS, Taleisnik J, et al. The arterial

anatomy of the human carpus: part I. the

extraosseous vascularity. J Hand Surg [Am] 8:

E 367, 1983.)

trapezium), os epilunatum (located between the scaphoid

and lunate), and the os radiostyloideum (located near the

radial styloid at the lateral border of the waist of the

scaphoid; see Fig. 1.27B) (25,46) (see descriptions earlier,

under Ossification Centers and Accessory Bones). The os

centrale exists as a free bone in lower primates (25).

The Bipartite Scaphoid

A bipartite scaphoid may be mistaken for a fracture. A

bipartite scaphoid arises from the failure of fusion of two

significant ossification centers. It often is bilateral. The

bipartite scaphoid may be distinguished from a fracture

from the lack of trauma history, bilaterality, and absence of

displacement or degenerative changes. It is possible to

injure the bipartite scaphoid, resulting in pain and a radiographic appearance resembling a fracture. Symptoms from

injury to a bipartite scaphoid usually resolve with a course

of protection or immobilization.

LUNATE (OS LUNATUM, SEMILUNAR)

Derivation and Terminology

The lunate derives its name from the Latin luna, meaning

“moon” (1), and is so named because of its crescent or

moon shape (as visualized on the lateral projection). The

British literature may refer to the lunate as the semilunar,

derived from semi, meaning “half” or “partly,” and lunar,

meaning “moon” (2).

Ossification Centers and Accessory Bones

The lunate is cartilaginous at birth. It usually has one ossification center that begins to ossify during the fourth year

(74) (see Fig. 1.27A). Variation in the ossification has been

noted, with ossification taking place at from 1.5 to 7 years

of age in boys, and between 1 and 6 years of age in girls

(89). Double ossification centers in the lunate also have

been noted (90,91).

Several accessory bones can be associated with the

lunate. Accessory bones, if present, usually are the result of

a secondary or additional ossification center that does not

fuse with the associated bone. Those associated with the

lunate include the os epilunatum (os centrale II), the os

hypolunatum (os centrale III), the os hypotriquetrum, the

os epitriquetrum (epipyramis, os centrale IV), and the os

triangulare (os intermedium antebrachii, os triquetrum

secundarium) (see Fig. 1.27B) (46). The os epilunatum is

located between the lunate, scaphoid, and capitate, along

the distal border of the scaphoid and lunate. The os hypolunatum is located between the lunate and the capitate, just

ulnar to the site of the os epilunatum. The os hypotriquetrum is located in the vicinity of the lunate, capitate,

proximal pole of the hamate, and the triquetrum. The os

epitriquetrum is located between the lunate, hamate, and

triquetrum, just ulnar to the site of the os hypotriquetrum.

The os triangulare is located between the lunate, triquetrum, and the distal ulna (46) (see Fig. 1.27B).

Osteology of the Lunate

The lunate is crescentic, concave distally and convex proximally (Fig. 1.30; see Figs. 1.25, 1.26, 1.37, and 1.38). It

consists internally of cancellous bone, surrounded by a cortical shell (see Fig. 1.30A,B). The dorsal and palmar surfaces are rough for the attachment of carpal ligaments. The

palmar surface is roughly triangular and is larger and wider

than the dorsal portion. The smooth, convex proximal

articular surface articulates with the lunate fossa of the distal radius and with a portion of the triangular fibrocartilage

on its proximoulnar aspect. The lateral surface is crescent

shaped, flat, and narrow, with a relatively narrow surface

area with which it contacts the scaphoid. The medial surface is square or rectangular, fairly flat, and articulates with

the triquetrum. The distal surface is deeply concave and

articulates with the proximal portion of the capitate.

Anomalies and Variations in Morphology

of the Lunate

Differences in lunate morphology have been discussed by

Taleisnik, Zapico, Viegas, Shepherd, and others (85,92a–95).

The lunate has been divided into three types, based on

whether its proximal aspect is curved or angulated. The

lunate shape is evaluated by measurements of the angle

between the lateral scaphoid side and the proximal radial

side of the lunate. The type I lunate has an angle greater

than 130 degrees and is present in approximately 30% of

those studied. The type I lunate has been associated with an

ulnar minus wrist. The type II lunate has an angle of

approximately 100 degrees, and is present in approximately

50%. The type III lunate has two distinct facets on the

proximal surface, one that articulates with the radius and

another that articulates with the triangular fibrocartilage.

The type III lunate is the least common, present in approximately 18% (85). The separate ulnar facet on the proximal

lunate, when present, has been noted to vary in size

between subjects (93).

Two types of lunate osseous morphology, based on the

presence or absence of a medial facet for hamate articulation, have been noted and described by Viegas and coworkers, Burgess, and Sagerman et al. (81,94–97). A type I

lunate is one in which there is no medial facet. Its reported

incidence is between 27% and 34.5% (81,94–96). A type II

lunate has a medial facet that articulates with the hamate.

The reported incidence is between 65.5% and 73%. The

size of the medial facet in the type II lunate ranges from a

shallow, 1-mm facet to a deep, 6-mm facet. In the type II

lunate with a large medial facet, there occasionally has been

50 Systems Anatomy

associated ridging on the capitate and hamate (81,95).

When the facet is large, it is easily identifiable radiographically and can be distinguished easily from the type I lunate.

However, when the medial facet is small in the type II

lunate, it may be difficult to distinguish it from a type I

lunate (81,97). With the type II lunate, carpal kinetics and

kinematics are different than in wrists with the type I

lunate. The type II lunate has been shown to be associated

with an increased incidence of cartilage erosion on the proximal pole of the adjacent, articulating hamate (see later,

under Clinical Implications).

Associated Joints

The lunate articulates with five bones: the radius, scaphoid,

capitate, hamate, and triquetrum (see Figs. 1.25, 1.26,

1.30, 1.37, and 1.38). The lunate articulates with the radius

on its proximal surface; it lies in the lunate fossa of the

radius, located on the ulnar aspect of the distal radius. The

lunate articulates with the scaphoid along the lunate’s radial

surface, with a relatively small, crescent-shaped articular

surface area. The lunate articulates with the capitate distally,

where the proximal pole of the capitate sits in the distal,

crescent-shaped articular surface of the lunate. The lunate

articulates with the triquetrum medially. In this area, the

articular surface of the lunate is rounded or oval. Between

the articular surfaces for the triquetrum and the capitate,

there usually is a narrow strip of articular surface for articulation with the proximal portion of the hamate. A curved

ridge separates the articular surfaces for the hamate and capitate. Contact with the hamate is maximized when the carpus is ulnarly deviated. Proximally, on the ulnar aspect of

the proximal articular surface of lunate, the lunate articulates with a portion of the triangular fibrocartilage complex.

Muscle Origins and Insertions

There are no muscle origins or insertions on the lunate.

Vascularity of the Lunate

The lunate receives its blood supply from both palmar and

dorsal sources or from the palmar aspect alone (see Fig.

1.29A,B). In 80% of specimens, the lunate receives nutrient

vessels from both the palmar and dorsal surfaces. In 20% of

specimens, it receives nutrient vessels from the palmar surface alone. Except for these relatively small dorsal and palmar surfaces, the lunate is covered by articular cartilage, and

thus no other vessels enter the bone. The vessels entering the

dorsal surface are from branches of the dorsal radiocarpal

arch, the dorsal intercarpal arch, and occasionally from

smaller branches of the dorsal branch of the anterior

1 Skeletal Anatomy 51

FIGURE 1.30. Right lunate. A: Proximolateral aspect. B: Distomedial aspect. C: Patterns of

intraosseous blood supply to the lunate (see text). (C after Gelberman RH, Bauman TD, Menon J,

et al. The vascularity of the lunate bone and Kienbock’s disease. J Hand Surg [Am] 5:272, 1980.)

A B

C

interosseous artery (73,98,99) (Fig. 1.29A). On the palmar

aspect, the lunate nutrient vessels are supplied by the palmar

intercarpal arch, the palmar radiocarpal arch, and communicating branches from the anterior interosseous artery and

the ulnar recurrent artery (Fig.1.29B).

The vessels that enter dorsally are slightly smaller than

those entering palmarly. Major vessels branch proximally

and distally after entering the bone and terminate in the

subchondral bone. The dorsal and palmar vessels anastomose intraosseously just distal to the mid-portion of the

lunate. The proximal pole has relatively less vascularity.

There are three major intraosseous patterns. These patterns take the shape of the letters “Y,” “I,” or “X” (see Fig.

1.30C). The Y pattern is the most common, occurring in

59% of studied specimens. The stem of the “Y” is oriented

dorsally or palmarly with equal frequency. The I pattern

occurs in approximately 30% of specimens, and consists of

a single dorsal and a single palmar vessel. The single dorsal

and single palmar vessels anastomose in a straight line, thus

forming the “I”-shaped pattern. The X pattern occurs in

10% of specimens and consists of two dorsal and two palmar vessels that anastomose in the center of the lunate, thus

forming an “X” (73,98,99).

In 20% of studied specimens, a single palmar supply was

noted. This pattern consists of a single large vessel that

enters on the palmar surface and branches in the lunate to

provide the sole blood supply.

Clinical Correlations: Lunate

The lunate and triquetrum usually begin to ossify in the

fourth and third years, respectively. Rarely, fusion of these

two ossification centers occurs, resulting in lunotriquetral

coalition. Of all of the carpal coalitions, lunotriquetral is

one of the most common (44,46,100–104).

Lunate ossification may be delayed in a variety of syndromes, including epiphyseal dysplasias and possible homocystinuria (81,105). Complete absence of the lunate also

has been reported (106).

The lunate has been divided into three types, based on

whether its proximal aspect is curved or angulated (see earlier, under Anomalies and Variations). The lunate shape is

evaluated by measurements of the angle between the lateral

scaphoid side and the proximal radial side of the lunate.

The type I lunate has an angle greater than 130 degrees and

is present in approximately 30% of those studied. The type

I lunate has been associated with an ulnar minus wrist.

Two types of lunate morphology based on the presence

or absence of a medial facet have been described by Viegas

and coworkers (see earlier, under Osteology) (81,94,95,

107,108). The carpal kinetics and kinematics have been

shown to be different in wrists with the two types of lunate

(109). The type II lunate contains a medial facet for articulation with the hamate. This has been associated with an

increased incidence of cartilage erosion with exposed bone

on the proximal pole of the hamate. These erosions usually

are not identifiable by radiography. The incidence of

hamate proximal pole erosions has been noted to be as high

as 44% with the type II lunate (containing the medial facet

articulating with the hamate). This is in contrast to the type

I lunate (which contains no medial facet), in which hamate

erosions or lesions were noted only in 0% to 2% (81,

95,107).

A triangular shape of the lunate on radiographs may

indicate a lunate dislocation, or tilting of the lunate in

either direction (dorsiflexion or palmar flexion). Dislocation of the lunate (or perilunate dislocation) is the most

common type of carpal dislocation.

The relatively small contact surface area between the

lunate and scaphoid (due, in part, to the narrow crescent

shape of the lunate) probably contributes to the difficulty in

achieving operative arthrodesis of the scapholunate joint.

Although fractures through the central portion of the

lunate are rare, loss of vascularity (Kienböck’s disease) is

associated initially with increased radiodensity, followed by

flattening or osseous collapse with fragmentation/fracture

in the later stages (110–112).

The Stages of Kienböck’s Disease (110,111)

n Stage I: Normal appearance on radiographs, possible linear or compression fracture on tomogram. Avascular

changes visualized on MRI. Bone scan shows abnormal

uptake.

n Stage II: Bone density changes (sclerosis), slight collapse

of radial border.

n Stage III: Fragmentation, collapse, cystic degeneration,

loss of carpal height, capitate proximal migration,

scaphoid rotation (scapholunate dissociation).

n Stage IV: Advance collapse, scaphoid rotation, sclerosis,

osteophytes of the radiocarpal joint.

Accessory Bones

Several accessory bones may be associated with the lunate

and can be mistaken for fractures. An accessory bone usually represents the residual of a secondary ossification center that does not fuse with the associated bone, but it also

may arise from trauma or from heterotopic ossification of

synovial tags (46,47). The accessory bones associated with

the lunate include the os epilunatum (located between the

lunate, scaphoid, and capitate), the os hypolunatum

(located between the lunate and capitate), the os hypotriquetrum (located between the lunate, capitate, proximal

pole of the hamate, and the triquetrum), os epitriquetrum

(located between the lunate, triquetrum, and proximal pole

of the hamate), and the os triangulare (located between the

lunate, triquetrum, and distal ulna; see Fig. 1.27B) (46) (see

descriptions earlier, under Ossification Centers and Accessory Bones).

52 Systems Anatomy

TRIQUETRUM (OS TRIQUETRUM,

TRIQUETRAL BONE, CUNEIFORM)

Derivation and Terminology

The name triquetrum is derived from the Latin for “threecornered” (1). The older British literature refers to the triquetrum as the cuneiform, derived from the Latin cuneus,

meaning “wedge,” and forma, meaning “likeness” or “form”

(2).

Ossification Centers and Accessory Bones

The triquetrum is cartilaginous at birth. It has one ossification center that begins to ossify during the third year (74)

(see Fig. 1.27A).

Several accessory bones can be associated with the triquetrum. Accessory bones, if present, are usually the result

of an additional or secondary ossification center that does

not fuse with the associated bone. Those associated with the

triquetrum include the os hypotriquetrum, the os epitriquetrum (os epipyramis, os centrale IV), the os triangulare

(os intermedium antebrachii, os triquetrum secundarium),

and the os ulnare externum (46) (see Fig. 1.27B). The os

hypotriquetrum is located in the vicinity of the triquetrum,

lunate, capitate, and the proximal pole of the hamate. The

os epitriquetrum is located between the triquetrum, lunate,

and proximal hamate, just ulnar to the site of the os

hypotriquetrum. The os triangulare is located between the

triquetrum, lunate, and the distal ulna (46) (see Fig.

1.27B).

Osteology of the Triquetrum

The triquetrum is pyramid-shaped and located on the proximoulnar aspect of the carpus (Fig. 1.31; see Figs. 1.25,

1.26, 1.37, and 1.38). Internally, the triquetrum consists of

cancellous bone, surrounded by a cortical shell (see Fig.

1.31). The triquetrum has several surfaces, including the

proximal, distal, lateral, dorsal, and palmar. The proximal

surface faces slightly medially, and contains both a rough,

nonarticular portion, and a lateral, slightly convex articular

portion that may “articulate” with the triangular fibrocartilage complex. The distal surface is directed laterally and

contains both concave and convex surface portions. The

distal surface is curved and smooth for articulation with the

medial surface of the hamate. The dorsal surface is rough

for the attachments of carpal ligaments. The palmar surface

contains two regions: medial and lateral. On the medial

region of the palmar surface is the articular surface for the

pisiform. This relatively small articular surface is round or

oval. The lateral portion of the palmar surface is rough and

nonarticular and provides attachments for carpal ligaments.

The lateral surface of the triquetrum forms the base of the

pyramid, which is flat and quadrilateral, for articulation

with the lunate. The medial and dorsal surfaces may be

somewhat confluent. The medial surface is the pointed

summit of the pyramid, and provides attachment for the

ulnar collateral ligament of the wrist.

Associated Joints

The triquetrum articulates with three bones: the lunate, the

pisiform, and the hamate (see Figs. 1.25, 1.26, 1.31, 1.37,

and 1.38). The articulation with the lunate on the radial

surface of the triquetrum is roughly square or rectangular,

or oval. The triquetrum articulates with the pisiform palmarly. The articular surface for the pisiform is round or oval

in shape. The articulation with the hamate is based distally

and slightly radially. The articular surface for the hamate is

smooth, curved, and slightly oval or triangular, extending

along the distoradial surface of the triquetrum.

Muscle Origins and Insertions

There are no muscle origins or insertions on the triquetrum.

Vascularity of the Triquetrum

The triquetrum receives its blood supply from branches

from the ulnar artery, the dorsal intercarpal arch, and the

palmar intercarpal arch (see Fig. 1.29A,B). Nutrient vessels

enter from the intercarpal arches and pass through its two

nonarticular surfaces, on the dorsal and palmar aspects.

The dorsal surface of the triquetrum is rough for attachments of associated carpal ligaments. This dorsal surface

contains a ridge that runs from the medial to the lateral

aspect. Two to four vessels enter this dorsal ridge and radiate in multiple directions to supply the dorsal 60% of the

bone. This network is the predominant blood supply to the

triquetrum in 60% of specimens (73,99).

The palmar surface contains an oval facet that articulates

with the pisiform. One or two vessels enter proximal and

distal to the facet. The vessels have multiple anastomoses

with each other and supply the palmar 40% of the bone.

This palmar vascular network is predominant in 20% of

specimens (99).

Significant anastomoses between the dorsal and the palmar vascular networks have been found in 86% of specimens studied (99).

1 Skeletal Anatomy 53

FIGURE 1.31. Right triquetrum. Distoradial aspect.

Clinical Correlations: Triquetrum

The triquetrum and the lunate usually begin to ossify in the

third and fourth years, respectively. Rarely, fusion of these

two ossification centers occurs, resulting in lunotriquetral

coalition. Of all of the carpal coalitions, lunotriquetral is

one of the most common (44,46,100–104).

Fractures of the triquetrum result from a direct blow or

from an avulsion injury that may include ligament damage.

The most common fracture is probably the impingement

shear fracture of the ulnar styloid against the dorsal triquetrum, occurring with the wrist in extension and ulnar

deviation, particularly when a long ulnar styloid is present

(97,113,114). An avulsion component also may be present.

A small bone fragment located dorsal to the triquetrum is

seen best on the lateral radiograph.

Accessory Bones

Several accessory bones may be associated with the triquetrum and can be mistaken for fractures. An accessory

bone usually represents the residual of a secondary ossification center that does not fuse with the associated bone, but it

also may arise from trauma or from heterotopic ossification

of synovial tags (46,47). The accessory bones associated with

the triquetrum include the os hypotriquetrum (located

between the triquetrum, lunate, capitate and the proximal

pole of the hamate), the os epitriquetrum (located between

the triquetrum, lunate, and proximal pole of the hamate, just

ulnar to the site of the os hypotriquetrum), the os triangulare

(located between the proximal triquetrum, lunate, and the

distal ulna), and the os ulnare externum (located at the distal

end of the triquetrum and adjacent to the ulnar border of the

distal hamate; see Fig. 1.27B) (46) (see descriptions earlier,

under Ossification Centers and Accessory Bones).

PISIFORM (OS PISIFORME)

Derivation and Terminology

The name pisiform is derived from the Latin pisum, meaning “pea,” and forma, meaning “likeness,” “shape,” or

“form” (1). Pisiform thus denotes “pea shaped.”

Ossification Centers and Accessory Bones

The pisiform is cartilaginous at birth. It has one ossification

center that begins to ossify in the ninth or tenth year in

girls, and in the twelfth year in boys (74) (see Fig. 1.27A).

It usually is the last carpal bone to ossify (5).

There is an accessory bone that can be associated with

the pisiform. The os pisiforme secundarium, also known as

the os ulnare antebrachii or the os metapisoid, is located at

the proximal pole of the pisiform (46) (see Fig. 1.27B). The

os pisiforme secundarium, if present, usually is the result of

an additional, secondary ossification center that does not

fuse with the pisiform.

Osteology of the Pisiform

The pisiform is the smallest carpal bone. It is situated at the

base of the hypothenar eminence on the medial side of the

wrist (Fig. 1.32; see Figs. 1.25 and 1.37). It lies palmar to

the triquetrum, in a plane palmar to the other carpal bones.

The pisiform actually is a sesamoid bone in the tendon of

the flexor carpi ulnaris. It consists internally of cancellous

bone, surrounded by a cortical shell (see Fig. 1.32). It is

generally spherical, although there is a slight long axis in the

distolateral direction (4,5). The pisiform is flat on its dorsal

surface, where the only articular surface is located. It articulates only with the triquetrum. The pisotriquetral joint is

not a portion of the radiocarpal joint, and there usually is

not a communication between these joints. The palmar surface of the pisiform is round and rough, and provides

attachments for the flexor carpi ulnaris (proximally) and the

abductor digiti minimi (distally). The lateral and medial

surfaces are rough. The lateral surface usually contains a

shallow groove that lies adjacent to the ulnar artery.

Associated Joints

The pisiform articulates with the triquetrum dorsally (see

Figs. 1.25, 1.32, and 1.37). This articular facet is flat and

oval, and is located slightly proximal on the dorsal surface.

Muscle Origins and Insertions

The flexor carpi ulnaris inserts onto the proximal palmar

edge of the pisiform, forming a crescent-shaped insertion

that is convex proximally and concave distally. The abductor digiti minimi (quinti) originates on the distal portion of

the pisiform, forming an oval origin area. The pisiform is

enclosed in these myotendinous structures (see Fig. 1.37).

There are no muscle origins or insertions on the dorsal

surface of the pisiform.

Vascularity of the Pisiform

The pisiform receives its blood supply through the proximal

and distal poles from branches of the ulnar artery (see Fig.

1.29A,B). The pisiform is a sesamoid bone in the tendon of

the flexor carpi ulnaris. The tendon attaches to the pisiform

proximally, and the proximal blood supply enters in this

area. One to three vessels penetrate inferior to the triquetral

54 Systems Anatomy

FIGURE 1.32. Right pisiform. Dorsal aspect.

facet. These proximally entering vessels divide into multiple

branches. Two superior branches run parallel beneath the

articular surface of the facet, and one or two inferior

branches run along the palmar cortex and anastomose with

the superior branches (99).

The distal vascular supply includes one to three vessels

that enter inferior to the articular facets, divide into superior and inferior branches, and run parallel to the palmar

cortex. These distally entering vessels anastomose with the

proximal vessels. The superior vessels run deep to the articular facet and communicate with the proximal superior vessels, forming an arterial ring deep to the facet. There are

multiple anastomoses between the proximal and the distal

vascular networks.

Clinical Correlations: Pisiform

Fracture of the pisiform can occur with a fall on the dorsiflexed, outstretched hand. Avulsion of its distal portion

with a vertical fracture can occur from a direct blow while

the pisiform is held firmly against the triquetrum under

tension from the flexor carpi ulnaris (67,113,115).

Accessory Bones

There is an accessory bone that can be associated with the

pisiform, the os pisiforme secundarium (Fig. 1.27B). It is

located at the proximal pole of the pisiform, and, if not

appreciated, it may be mistaken for a fracture. An accessory

bone usually represents the residual of a secondary ossification center that does not fuse with the associated bone, but it

also may arise from trauma or heterotopic ossification of synovial tags (46,47).

HAMATE (OS HAMATUM, UNCIFORM)

Derivation and Terminology

Hamate is derived from the Latin hamulus, meaning

“hook,” and hamatum, meaning “hooked” (1). The hamate

also may be referred to as the unciform bone, derived from

the Latin uncus, also meaning “hook,” and forma, meaning

“likeness,” “shape,” or “form” (2).

Ossification Centers and Accessory Bones

The hamate is cartilaginous at birth. It has one ossification

center that begins to ossify at the end of the third month. Of

all the carpal bones, the hamate usually is the second to ossify

(after the capitate) and, on occasion, ossification already may

have started at birth (5,74–76) (see Fig. 1.27A).

Several accessory bones can be associated with the

hamate. Accessory bones, if present, usually are the result of

a secondary or additional ossification center that does not

fuse with the associated bone. Those associated with the

hamate include the os hamuli proprium, os hamulare basale

(carpometacarpale VII), os hypotriquetrum, os epitriquetrum (os epipyramis, os centrale IV), os ulnare externum, os vesalianum manus (os vesalii, os carpometacarpale

VIII), os gruberi (os carpometacarpale VI), and os capitatum secundarium (carpometacarpale V) (see Fig. 1.27B)

(46). The os hamuli proprium is a secondary ossification

center in the hook of the hamate that does not fuse with the

body. It is located in the palmar aspect of the mid-body,

where the hook usually is located. The os hamulare basale is

located between the distal body of the hamate and the base

of the ring finger metacarpal. The os hypotriquetrum is

located proximal to the proximal pole of the hamate, adjacent to the lunate, capitate, and triquetrum. The os epitriquetrum is located proximal to the proximal pole of the

hamate, adjacent to the triquetrum and lunate, just ulnar to

the site of the os hypotriquetrum. The os ulnare externum

is located ulnar to the distal body of the hamate, distal to

the triquetrum. The os vesalianum manus is located proximal to the small finger metacarpal, near the styloid. The os

gruberi is located at the radiodistal margin of the body of

the hamate, between the hamate, capitate, and the base of

the ring and base of the long finger metacarpals. The os capitatum secundarium is located just radial to the site of the

os gruberi, at the radiodistal margin of the hamate body and

between the capitate and bases of the ring and long finger

metacarpals (46) (see Fig. 1.27B).

Osteology of the Hamate

The hamate consists of a body, a proximal pole, and a hook

(hamulus; Fig. 1.33; see Figs 1.25, 1.26, 1.37, and 1.38). It

1 Skeletal Anatomy 55

FIGURE 1.33. Right hamate. A: Medial aspect. B: Inferolateral aspect.

A B

consists internally of cancellous bone, surrounded by a cortical shell (see Fig. 1.33). The hamate is an irregularly shaped

bone with an unciform hamulus (hook). The hook is located

on the distal portion of the palmar surface, slightly closer to

the medial aspect. The hook projects palmarly from the

rough palmar surface. The hook is slightly curved, with its

convexity medial and concavity lateral. The tip of the hook

has a slight lateral inclination and serves as a point of attachment for a portion of the transverse carpal ligament. The

hook of the hamate and the pisiform contribute to the

medial wall of the carpal tunnel. The convex (medial) side of

the hook is rough. The concave (lateral) side is smooth

where the adjacent flexor tendons to the small finger pass. At

the base of the hook, on the medial side, there may be a

slight transverse groove in which the terminal deep branch

of the ulnar nerve may contact as it passes distally.

The body of the hamate is somewhat triangular or

cuneiform (wedge shaped), with a wide distal portion and a

narrowing into an apex proximolaterally. The dorsal and

palmar surfaces of the body are largely nonarticular, and are

rough for attachments of the carpal ligaments. The distal,

wide surface of the hamate consists of the articular surfaces

for the base of the small and ring finger metacarpals. The

articular surface thus has two facets, one for each

metacarpal, separated by a slight intraarticular ridge. The

facet for the ring finger metacarpal is smaller than that for

the small finger metacarpal. The proximal surface narrows

into a thin margin of the wedge-shaped body. At the tip of

the proximal surface there usually is a small, narrow facet

for articulation of the lunate. The hamate may be in contact with the lunate only during ulnar deviation of the

wrist. The medial surface of the body of the hamate is broad

and somewhat rectangular. In contains the relatively large

articular surface for articulation with the triquetrum. The

surface is curved, with a convexity proximally that becomes

concave distally. At the distal aspect of the medial side of

the body, there is a narrow medial strip that is nonarticular.

On the lateral surface of the body of the hamate, the relatively large surface is nearly completely articular, with the

exception of a small area on the distal palmar angle. The

proximal portion or the lateral aspect is convex, and the distal portion is slightly concave. The lateral aspect articulates

with the capitate.

Associated Joints

The hamate articulates with five bones: the triquetrum, the

capitate, the base of the ring and small finger metacarpals,

and the small articulation with the lunate (see Figs. 1.25,

1.26, 1.33, 1.37, and 1.38). The hamate articulation with

the triquetrum is along the proximal and medial aspects,

through a relatively large, oval-shaped articular surface area.

The hamate articulates with the capitate along its lateral

surface, also involving a relatively large, oval articular surface area. The hamate articulates with the base of the

metacarpals through two facets, one to the small and one to

the ring finger. The articulation with the small finger

metacarpal usually involves a much larger articular facet. In

addition, the very most proximal portion articulates with

the lunate, especially when the wrist is ulnarly deviated.

Muscle Origins and Insertions

The opponens digiti minimi and flexor digiti minimi originate from the palmar ulnar surface of the hook of the

hamate (see Figs. 1.37 and 1.38). In addition, a small portion of the flexor carpi ulnaris may insert into the palmar

aspect of the hamate (the major insertion of the flexor carpi

ulnaris is into the proximal portion of the palmar surface of

the pisiform) (2).

There are no muscle origins or insertions on the dorsal

surface of the hamate.

Vascularity of the Hamate

The vascularity of the hamate is supplied from three main

sources: the dorsal intercarpal arch, the ulnar recurrent

artery, and the ulnar artery (see Fig. 1.29A,B). The vessels

enter through the three nonarticular surfaces of the hamate,

which include the dorsal surface, the palmar surface, and

the medial surface through the hook of the hamate. These

nonarticular surfaces of the hamate are somewhat rough for

attachment of carpal ligaments.

The dorsal surface is triangular in shape and receives three

to five vessels. These branch in several directions to supply

the dorsal 30% to 40% of the bone (73,99). Small foramina

usually are easily visible on the dorsal surface.

The palmar surface also is triangular and usually receives

one large vessel that enters through the radial base of the

hook. It then branches and anastomoses with the dorsal vessels in 50% of studied specimens (73,99).

The hook of the hamate receives one or two small vessels

that enter through the medial base and tip of the hook.

These vessels anastomose with each other but usually not

with the vessels to the body of the hamate.

Clinical Correlations: Hamate

Fracture of the hook of the hamate often occurs in sportsrelated use of clubs, bats, or racquets (116). Direct force

exerted by these objects against the hypothenar eminence or

transverse carpal ligament has been implicated (67,116).

Fracture of the hook of the hamate often is not visible on

standard radiographs. It may be visualized with the carpal tunnel view. Alternatively, trispiral, computed tomography or

MRI may show difficult-to-visualize fractures.

Untreated displaced fractures of the hook of the hamate

may lead to attrition rupture of the flexor tendons to the

small finger because these tendons pass against the hook

and can be subject to wear from contact and friction against

56 Systems Anatomy

a jagged fracture surface. A patient with a hook of the

hamate fracture may perceive pain on the dorsum of the

hamate and palpation over the hook on the palmar side

usually elicits tenderness.

The incidence and location of arthrosis and chondromalacia (with cartilage erosions and exposed subchondral

bone) is among the highest at the proximal pole of the

hamate. Chondromalacia was found in 16.8%; arthrosis

with exposed subchondral bone was found in 28.2% (94).

Arthrosis at the proximal pole of the hamate also is associated with the presence of a mid-carpal plica. A mid-carpal

plica was identified in 1% of 393 wrists. All wrists that had

a mid-carpal plica also were found to have arthrosis at the

proximal pole of the hamate (94).

Accessory Bones

Several accessory bones may be associated with the hamate

and can be mistaken for fractures (Fig. 1.27B). An accessory

bone usually represents the residual of a secondary ossification center that does not fuse with the associated bone, but

it also may arise from trauma or heterotopic ossification of

synovial tags (46,47). The accessory bones associated with

the hamate include the os hamuli proprium (located in the

area of the hook), the os hamulare basale (located at the distal margin of the hamate, in the vicinity of the bases of the

long and ring finger metacarpals), the os hypotriquetrum

(located proximal to the proximal pole of the hamate, adjacent of the lunate, capitate, and triquetrum), the os epitriquetrum (located proximal to the proximal pole of the

hamate, in the vicinity of the lunate, capitate, and triquetrum, just ulnar to the site of the os hypotriquetrum),

the os ulnare externum (located ulnar to the body of the

hamate, just distal to the triquetrum), the os vesalianum

manus (locate ulnar and slightly distal to the hamate, near

the styloid process of the base of the small finger

metacarpal), the os gruberi (located at the distoradial corner

of the hamate, adjacent to the capitate and bases of the long

and ring finger metacarpals), and os capitatum secundarium (located at the distoradial corner of the hamate, adjacent to the capitate and bases of the long and ring finger

metacarpals, just radial to the site of the os gruberi; see Fig.

1.27B) (46) (see descriptions earlier, under Ossification

Centers and Accessory Bones).

CAPITATE (OS CAPITATUM, OS MAGNUM)

Derivation and Terminology

The name capitate is derived from the Latin caput, meaning

“head.” Capitate denotes “head-shaped” (1). It also has been

suggested that the word capitate indicates the “head” of the

wrist because it is the largest bone of the carpus. The older

British literature may refer to the capitate as the os magnum,

derived from magnum, indicating “large” (2).

Ossification Centers and Accessory Bones

The capitate usually is cartilaginous at birth. It has one ossification center that begins to ossify in the second month.

Of all the carpal bones, the capitate (or hamate) usually is

the first to ossify, and occasionally ossification already may

have started at birth (5,74–76) (see Fig. 1.27A).

Several accessory bones can be associated with the capitate. Accessory bones, if present, usually are the result of a

secondary or additional ossification center that does not

fuse with the associated bone. Those associated with the

capitate include the os subcapitatum, os capitatum secundarium (carpometacarpale V), os gruberi (os carpometacarpale VI), os hypotriquetrum, os epitriquetrum

(epipyramis, os centrale IV), os hypolunatum (os centrale

III), os epilunatum (os centrale II), os centrale (os centrale

dorsale, os episcaphoid), os metastyloideum, os parastyloideum (os carpometacarpale III), and os styloideum (carpometacarpale IV) (see Fig. 1.27B) (25,46). The os subcapitatum is located adjacent to the central portion of the body

of the capitate. The os capitatum secundarium is located at

the distoulnar corner of the capitate, adjacent to the distal

hamate, and the bases of the longer and ring finger

metacarpals. The os gruberi is located just ulnar to the site

of the os capitatum secundarium, at the distoulnar corner

of the capitate and adjacent to the bases of the ring and long

metacarpals. The os hypotriquetrum is located ulnar to the

base of the capitate, proximal to the proximal pole of the

hamate, and adjacent to the triquetrum and lunate. The os

epitriquetrum is located just ulnar to the site of the os

hypotriquetrum, proximal to the proximal pole of the

hamate, and adjacent to the triquetrum and lunate. The os

hypolunatum is located just proximal to the proximal margin of the capitate, between the lunate and adjacent to the

proximal pole of the scaphoid. The os epilunatum is located

between the capitate, lunate, and scaphoid, just radial to the

site of the os hypolunatum. The os centrale is located

between the capitate, scaphoid, and trapezoid. The os

metastyloideum is located at the distoradial aspect of the

capitate, between the trapezoid and base of the index finger

metacarpal. The os parastyloideum is located at the distoradial aspect of the capitate, slightly distal to the site for the

os metastyloideum, between the capitate and base of the

index and long finger metacarpals. The os styloideum is

located at the distal aspect of the capitate, just ulnar to the

site for the os parastyloideum, between the capitate and the

base of the index and long finger metacarpals (46) (see Fig.

1.27B).

Osteology of the Capitate

The capitate is the largest and centrally located carpal bone,

containing articulations with the lunate, scaphoid, trapezoid, the long, index, and ring finger metacarpals, the

hamate, and the triquetrum (Fig. 1.34; see Figs. 1.25, 1.26,

1 Skeletal Anatomy 57

1.37, and 1.38). It consists internally of cancellous bone,

surrounded by a cortical shell (see Fig. 1.34). It is elongated

in the proximo distal direction, and thus contains a longitudinal axis. There is a slight concavity to the dorsal, radial,

and ulnar surfaces, thereby producing a “waist” that is narrowed and located slightly proximal to the transverse midline. The dorsal surface is larger than the palmar surface.

Both are rough for attachment of carpal ligaments. The palmar surface is flat or slightly convex. The proximal pole is

rounded. The distal end is flattened with slightly squared

corners on the medial and lateral aspects. The distal surface,

which is transverse to its axis, is triangular (apex located palmarly), with both a concave and a convex component. The

distal articulation is mainly with the base of the long finger

metacarpal. There are slight variations as to the specific

articulations distally (see later, under Anomalies and Variations). The medial and lateral borders are somewhat concave. The lateral border usually has a narrow concave strip

for the medial side of the base of the index metacarpal. The

dorsal medial angle of the distal aspect usually (approximately 86% of wrists) has a facet for the articulation with

the base of the ring finger metacarpal. This small facet may

be absent in 14% (81,94,117). The relatively large head of

the capitate, consisting of the proximal rounded pole, projects into the concavity formed by the lunate and scaphoid.

The proximal surface articulates with the lunate and the

proximal portion of the lateral surface articulates with the

scaphoid. Along the distolateral surface, there is a separate

facet for the trapezoid. This facet may be separated from the

facet for the scaphoid by a rough interval. The medial surface of the capitate has a relatively large, concave facet for

the hamate.

Anomalies and Variations in Morphology

of the Capitate

The distal aspect of the capitate articulates mainly with the

base of the long finger metacarpal. In 84% to 86% of

wrists, the capitate also has a small, narrow facet for articulation with the base of the ring finger metacarpal

(94,117,118). The capitate–ring finger metacarpal articulation, when present, usually is easily identifiable on standard

radiographs (118). A separate facet for articulation with the

ring finger metacarpal was found to be absent on the capitate in 14% of wrists (81,94,117).

Associated Joints

The capitate articulates with seven bones, largely with the

lunate, scaphoid, trapezoid, the base of the long finger

metacarpal, and the hamate (see Figs. 1.25, 1.26, 1.34,

1.37, and 1.38). There are smaller articulations with the

base of the index and ring finger metacarpals, and, with

the wrist in certain positions (radial deviation), with the

triquetrum. The capitate articulates with the lunate proximally, where the capitate’s proximal pole sits deep in the

crescent-shaped fossa of the lunate, forming a major portion of the mid-carpal joint. The capitate also articulates

with the scaphoid proximally and radially; the articular

surface of the capitate is irregular and somewhat oval, and

encompasses the proximal portion of the lateral border of

the capitate. The capitate articulates with the trapezoid

on the distal portion of its lateral border through a relatively small articular surface area. Distally, the capitate

articulates largely with the base of the long finger

metacarpal. On the distal radial corner of the capitate,

there is a smaller articulation with the ulnar proximal corner of the base of the index metacarpal. Along a small

strip of the distal ulnar corner of the capitate, there also

is a narrow articulation with the radial proximal corner of

the base of the ring finger metacarpal. (Thus, the capitate

articulates with three metacarpals: the index, long, and

ring fingers.) Along the entire concave ulnar border of the

capitate, there is a long, somewhat ovoid articulation

with the body and proximal pole of the hamate. At the

proximal ulnar border of the capitate there is a potential

small articulation with the triquetrum when the wrist is

radially deviated.

58 Systems Anatomy

FIGURE 1.34. Right capitate. A: Medial aspect. B: Lateral aspect.

A B

Muscle Origins and Insertions

Approximately half of the oblique head of the adductor pollicis (adductor pollicis obliquus) originates from the distal

radial part of the palmar surface of the capitate (see Figs.

1.37 and 1.38). The base of the long finger metacarpal

serves for the other, distal half of the origin of the oblique

head; the trapezoid also may contain a small portion of the

origin of the oblique head of the adductor pollicis.

There are no muscle origins or insertions on the dorsal

surface of the capitate.

Vascularity of the Capitate

The capitate receives its vascularity from both dorsal and

palmar sources. The main vascularity originates from vessels

from the dorsal intercarpal and dorsal basal metacarpal

arches, as well as from significant anastomoses between the

ulnar recurrent and palmar intercarpal arches (see Fig.

1.29A,B). The vessels that enter the capitate penetrate

through the two nonarticular surfaces on the dorsal and palmar aspects of the bone.

The dorsal surface of the capitate is rough for attachments

of the dorsal carpal ligaments. The dorsal surface is broad, relatively wide, and contains a deeply concave portion. Two to

four nutrient vessels enter the distal two-thirds of the dorsal

concavity. Smaller vessels occasionally enter more proximally,

near the neck. Multiple small foramina usually are visible in

this dorsal portion of the capitate. The entering dorsal vessels

course palmarly, proximally, and ulnarly within the capitate

in a retrograde fashion to supply the body and head. This

dorsal supply continues palmarly and proximally, eventually

reaching the vicinity of the convex rough palmar surface. Terminal vessels reach the proximal palmar head and terminate

just deep to the articular surface (73,99).

The palmar vascular contribution is through one to three

vessels. These vessels enter the palmar surface on the distal

half of the capitate and course proximally in a retrograde

fashion. Small foramina may be visible in this palmar area

of the capitate. In 33% of studied specimens, the vascularity to the capitate head originated entirely from the palmar

surface. There are notable anastomoses between the dorsal

and the palmar blood supplies in 30% of specimens studied

(73,99).

Clinical Correlations: Capitate

The capitate is rarely fractured because of its protected position in the carpus.

The “naviculocapitate syndrome” consists of fracture of

the capitate and the scaphoid, with the proximal capitate

fragment rotated 90 to 180 degrees. The articular surface thus

is displaced anteriorly or faces the fracture surface of the capitate neck (119). (Also known as scaphocapitate syndrome.)

Accessory Bones

Several accessory bones may be associated with the capitate

and can be mistaken for fractures. An accessory bone usually represents the residual of a secondary ossification center that does not fuse with the associated bone, but it also

may arise from trauma or from heterotopic ossification of

synovial tags (46,47). The accessory bones associated with

the capitate include the os subcapitatum (located adjacent

to the distal body), the os capitatum secundarium (located

between the capitate and bases of the long and ring finger

metacarpals), the os gruberi (located between the capitate

and bases of the ring and long finger metacarpals, just ulnar

to the site for the os capitatum secundarium), the os

hypotriquetrum (located between the capitate, proximal

pole of the hamate, triquetrum, and lunate), the os epitriquetrum (located between the capitate, proximal pole of the

hamate, triquetrum, and lunate, just ulnar to the site for the

os hypotriquetrum), the os hypolunatum (located between

the capitate, lunate, and scaphoid, just ulnar to the site of

the os epilunatum), the os epilunatum (located between the

capitate, lunate, and scaphoid), the os centrale (located

between the capitate, scaphoid, and trapezoid), the os

metastyloideum (located between the capitate, trapezoid,

and base of the index finger metacarpal), the os parastyloideum (located between the capitate and bases of the

index and long finger metacarpals), and the os styloideum

(located between the capitate and bases of the index and

long finger metacarpals, just ulnar to the site for the os

parastyloideum; see Fig. 1.27B) (46) (see descriptions earlier, under Ossification Centers and Accessory Bones).

TRAPEZOID (OS TRAPEZOIDEUM,

OS MULTANGULUM MINUS, LESSER

MULTANGULAR)

Derivation and Terminology

The name is derived from the Latin trapezoides and the

Greek trapezoeides, both indicating “table-shaped.” This has

been extrapolated to denote a four-sided plane, with two

sides parallel and two diverging (1). The word multangular

pertains to “many-sided.”

Ossification Centers and Accessory Bones

The trapezoid is cartilaginous at birth. It has one ossification center that begins to ossify during the fourth year in

girls and in the fifth year in boys (74) (see Fig. 1.27A).

Several accessory bones can be associated with the trapezoid. Accessory bones, if present, usually are the result of a

secondary or additional ossification center that does not

fuse with the associated bone. Those associated with the

trapezoid include the os trapezoideum secundarium (mul1 Skeletal Anatomy 59

tangulum minus secundarium), the os metastyloideum, the

os centrale (centrale dorsale, episcaphoid), and the os

trapezium secundarium (multangulum majus secundarium,

carpometacarpale II) (see Fig. 1.27B) (46). The os trapezoideum secundarium is located at the distal radial corner

of the trapezoid, between the trapezoid and the radial base

of the index finger metacarpal. The os metastyloideum is

located at the distal ulnar corner of the trapezoid, between

the trapezoid and the ulnar base of the index finger

metacarpal. The os centrale is located between the trapezoid, scaphoid, and capitate. The os trapezium secundarium

is located at the radial margin of the trapezoid, between the

trapezoid, trapezium, and base of the thumb and index

metacarpals (46) (see Fig. 1.27B).

Osteology of the Trapezoid

The trapezoid is a small, irregular carpal bone, with somewhat of a mushroom, wedge, or T-shape, larger dorsally

than palmarly (Fig. 1.35; see Figs. 1.25, 1.26, 1.37, and

1.38). It consists internally of cancellous bone, surrounded

by a cortical shell (see Fig. 1.35). The trapezoid is the smallest bone in the distal carpal row. When viewed dorsally, the

dorsal surface is oval, elongated in the radioulnar direction.

Its dorsal surface is rough. The smaller palmar portion is a

projection from the wide dorsal portion, connecting to the

dorsal portion slightly laterally. When viewed palmarly, the

palmar portion is round or slightly squared. The distal surface articulates with a groove in the base of the index

metacarpal. The distal surface is triangular, with the apex

palmar. This distal articular surface is convex, containing

two smaller concave facet-like surfaces located radially and

ulnarly. The medial surface articulates with the distal, radial

part of the capitate. The medial articular surface on the

trapezoid is narrow and concave from dorsal to palmar. The

narrow lateral surface of the trapezoid is convex and smooth

and articulates with the trapezium. The proximal portion

articulates with the scaphoid tuberosity articular surface,

forming the ulnar facet of the triscaphe joint.

Associated Joints

The trapezoid articulates with four bones: the base of the

index finger metacarpal, the capitate, the scaphoid, and the

trapezium (see Figs. 1.25, 1.26, 1.35, 1.37, and 1.38).

Along its distal surface, the trapezoid articulates with base

of the index metacarpal, where the trapezoid sits in a groove

of the metacarpal. The trapezoid articulates along its ulnar

border with the capitate, where the trapezoid contains a

small rectangular facet on the ulnar aspect near the palmar

surface. The trapezoid articulates proximally with the

scaphoid, forming the ulnar component of the triscaphe

joint. The trapezoid also articulates radially with the trapezium, where a convex surface of the lateral border of the

trapezoid sits in a concave articular surface of the trapezium. The four articular surfaces of the trapezoid all connect

with each other, each separated by a relatively sharp edge.

Muscle Origins and Insertions

The trapezoid gives origin to one, and possibly two muscles: the deep head of the flexor pollicis brevis, and, variably,

to a small portion of the origin of the adductor pollicis

(oblique head; see Figs. 1.37 and 1.38).

The deep head of the flexor pollicis brevis originates

from the palmar aspect of the trapezoid. (The superficial

head originates from the transverse carpal ligament and

from the palmar aspect of the trapezium.) The flexor pollicis brevis inserts into the radial sesamoid and into the radial

aspect of the base of the proximal thumb metacarpal.

A small portion of the origin of the adductor pollicis

oblique head (adductor pollicis obliquus) may originate

from the distal ulnar corner of the palmar surface of the

trapezoid. (The major origins of the adductor pollicis

obliquus are from the base of the long metacarpal and distal portion of the palmar surface of the capitate.)

There are no muscle origins or insertions on the dorsal

surface of the trapezoid.

Vascularity of the Trapezoid

The trapezoid is supplied by branches from the dorsal intercarpal and basal metacarpal arches and the radial recurrent

artery (see Fig. 1.29A,B). The nutrient vessels enter the

trapezoid through its two nonarticular surfaces on the dorsal and palmar surfaces.

The main blood supply of the trapezoid is from the dorsal supply. The dorsal surface is broad and flat, where the

nonarticular surface serves for attachment of carpal ligaments. Three or four small vessels enter the dorsal surface in

60 Systems Anatomy

FIGURE 1.35. Right trapezoid. A: Medial aspect. B: Inferolateral aspect.

A B

the central aspect of the rough surface. Multiple small

foramina usually are visible in this dorsal area. After penetrating the subchondral bone, the vessels branch to supply

the dorsal 70% of the bone. These dorsal vessels provide the

primary vascularity of the trapezoid (99).

The palmar blood supply provides vascularity to approximately 30% of the trapezoid. The palmar surface is narrow,

flat, and relatively small, and contains a small nonarticular

portion where ligaments attach. In this area, one or two small

vessels penetrate the central palmar portion. After entering

the palmar surface of the trapezoid, the vessels branch several

times to supply the palmar 30% of the bone. The palmar vessels do not anastomose with the dorsal vessels (99).

Clinical Correlations: Trapezoid

Fractures of the trapezoid are rare because of its protected

position and its shape. Axial loading of the second metacarpal

can cause dorsal (or, more rarely, palmar) dislocation, with

associated rupture of the capsular ligaments (120).

Because of the wedge or mushroom shape of the trapezoid (with the wide portion dorsally), dislocations are much

more apt to occur dorsally than palmarly.

Oblique radiographs and tomography may be helpful to

visualize trapezoid fractures because the trapezoid is difficult to visualize on routine posteroanterior, anteroposterior,

or lateral views of the wrist.

Accessory Bones

Several accessory bones may be associated with the trapezoid and can be mistaken for fractures. An accessory bone

usually represents the residual of a secondary ossification

center that does not fuse with the associated bone, but it

also may arise from trauma or heterotopic ossification of

synovial tags (46,47). The accessory bones associated with

the trapezoid include the os trapezoideum secundarium

(located between the trapezoid, index finger metacarpal,

and trapezium), the os metastyloideum (located between

the trapezoid, base of the index finger metacarpal, and the

capitate), the os centrale (located between the trapezoid,

scaphoid, and capitate), and the os trapezium secundarium

(located between the trapezoid, trapezium, and the vicinity

of the bases of the index and thumb metacarpals; see Fig.

1.27B) (46) (see descriptions earlier, under Ossification

Centers and Accessory Bones).

TRAPEZIUM (OS TRAPEZIUM,

OS MULTANGULUM MAJUS,

GREATER MULTANGULAR)

Derivation and Terminology

The name is derived from the Latin and Greek trapezion,

indicating an irregular four-sided figure. The word multangular denotes “many-sided.”

Ossification Centers and Accessory Bones

The trapezium is cartilaginous at birth. It has one ossification center that begins to ossify during the fourth year in

girls and the fifth year in boys (5,74) (see Fig. 1.27A).

Several accessory bones can be associated with the

trapezium. Accessory bones, if present, usually are the result

of a secondary or additional ossification center that does

not fuse with the associated bone. Those associated with the

trapezium include the os trapezium secundarium (multangulum majus secundarium, carpometacarpale II), the os

praetrapezium (carpometacarpale I), the os paratrapezium,

the os epitrapezium, the os radiale externum (parascaphoid), and the os trapezoideum secundarium (multangulum minus secundarium) (see Fig. 1.27B) (46). The os

trapezium secundarium is located between the trapezium

and the ulnar base of the thumb metacarpal. The os praetrapezium is located between the distal aspect of the trapezium and the thumb metacarpal. The os paratrapezium is

located between the distoradial aspect of the trapezium and

the radial base of the thumb metacarpal. The os epitrapezium is located at the proximal aspect of the trapezium,

between the trapezium and distoradial aspect of the

scaphoid. The radiale externum is located between the

trapezium and the distal scaphoid, proximal to the site of

the os epitrapezium (46) (see Fig. 1.27B).

Osteology of the Trapezium

The trapezium is the most radially located carpal bone,

assuming a functionally strategic position at the base of the

thumb metacarpal and positioned just distal to the scaphoid

(Fig. 1.36; see Figs. 1.25, 1.26, 1.37, 1.38, and 1.39). It

consists internally of cancellous bone, surrounded by a cortical shell (see Fig. 1.36). The trapezium has an irregular

shape. The dorsal and palmar surfaces are rough. The dorsal surface is wide and may contain a slight indentation or

groove along which the radial artery passes. The palmar

surface is narrow and contains a deep groove on the palmar ulnar surface. The groove forms the osseous portion

of the fibroosseous tunnel containing the flexor carpi radialis tendon. Radial to the groove is a distinct longitudinal

ridge (trapezial ridge) running in the proximodistal direction. The trapezial ridge provides attachment for a portion

of the transverse carpal ligament (flexor retinaculum). The

trapezial ridge and palmar surface of the trapezium also

provide origins for the abductor pollicis brevis, opponens

pollicis, and flexor pollicis brevis muscles. The lateral surface of the trapezium is broad and rough for attachment

of carpal ligaments. The trapezium contains four articular

surfaces for articulations with the scaphoid, trapezoid,

index finger metacarpal, and the thumb metacarpal. The

proximal articular surface is relatively small, and contains

the facet for the scaphoid. The distal articular surface is

relatively large and oval and saddle shaped. This distal

1 Skeletal Anatomy 61

articular surface articulates with the thumb metacarpal.

This large sellar (“saddle-shaped”) joint allows unique

mobility. The surface shape has been found to be fundamentally different in men and women. The surface area

also is significantly smaller in women (121). The ulnar

aspect of the trapezium is concave, and contains the articular surface for the trapezoid. A small area on the distal

ulnar aspect contains a narrow oval facet for articulation

with the radial base of the index finger metacarpal.

Associated Joints

The trapezium articulates with four bones: the scaphoid,

thumb metacarpal, trapezoid, and a small portion of the

index metacarpal (see Figs. 1.25, 1.26, and 1.36 to 1.38).

The trapezium articulates proximally with the scaphoid,

forming an important component of the triscaphe joint.

The articular surface on the trapezium for the scaphoid is

somewhat square or rectangular. Distally and radially, the

trapezium articulates with the thumb metacarpal through a

saddle-shaped articulation. The trapezium articulates with

the trapezoid along its medial border, where the articular

surface on the trapezium is somewhat square. Distally and

medially, there is a relatively small articulation of the trapezium with the index metacarpal. This joint surface on the

trapezium is somewhat square or rectangular.

Muscle Origins and Insertions

The palmar surface of the trapezium contains origins of the

three thenar muscles: abductor pollicis brevis, flexor pollicis

brevis (superficial head), and opponens pollicis (see Figs.

1.37 and 1.38). These muscles attach to the palmar surface

or just lateral to the trapezial ridge. Although the flexor

carpi radialis does not actually insert into the trapezium, it

traverses through a fibroosseous tunnel along the ulnar

aspect of the trapezium.

There are no muscle origins or insertions on the dorsal

surface of the trapezium.

Vascularity of the Trapezium

The vascularity of the trapezium is from vessels from the

distal branches of the radial artery (see Fig. 1.29A,B).

Nutrient vessels enter the trapezium through its three

nonarticular surfaces. These surfaces are the dorsal and lateral aspects, which are rough and serve as sites for ligamentous attachment, and the prominent palmar tubercle from

which the thenar muscles arise. Dorsally, one to three vessels enter and divide in the subchondral bone to supply the

entire dorsal aspect of the bone. Palmarly, one to three vessels enter the mid-portion and divide and anastomose with

the vessels entering through the dorsal surface. Laterally,

three to six very fine vessels penetrate the lateral surface and

anastomose freely with the dorsal and palmar vessels. The

dorsal vascular supply usually supplies most of the vascularity. There are frequent anastomoses among all three systems. The associated dorsal, palmar, and lateral surfaces of

the trapezium contain multiple foramina for the nutrient

vessels (83,99).

Clinical Correlations: Trapezium

Fracture of the articular surface of the trapezium is produced by the base of the thumb metacarpal being driven

into the articular surface of the trapezium by the adducted

thumb (67,122).

Avulsion fractures caused by capsular ligaments can

occur during forceful deviation, traction, or rotation (115).

Fracture of the trapezial ridge may occur from a direct

blow to the palmar arch or forceful distraction of the proximal palmar arch to result in avulsion of the ridge of the

trapezium by the transverse carpal ligament (123,124). The

carpal tunnel view radiograph may be required to visualize

this fracture.

Accessory Bones

Several accessory bones may be associated with the trapezoid and can be mistaken for fractures. An accessory bone

62 Systems Anatomy

FIGURE 1.36. Right trapezium. A: Palmar aspect. B: Medial aspect.

A B

usually represents the residual of a secondary ossification

center that does not fuse with the associated bone, but it

also may arise from trauma or heterotopic ossification of

synovial tags (46,47). The accessory bones associated

with the trapezium include the os trapezium secundarium

(located between the trapezium and the base of the

thumb metacarpal), the os praetrapezium (located

between the distal trapezium and central portion of the

base of the thumb metacarpal), the os paratrapezium

(located between the trapezium and the radial aspect of

the base of the thumb metacarpal), the os epitrapezium

(located between the trapezium and scaphoid), the os

radiale externum (located between the trapezium and

scaphoid, just proximal to the site for the os epitrapezium), and the os trapezoideum secundarium (located

between the trapezium, trapezoid, and basses of the index

and thumb metacarpals; see Fig. 1.27B) (46) (see descriptions earlier, under Ossification Centers and Accessory

Bones).

METACARPALS (OSSA METACARPALIA)

Derivation and Terminology

The word metacarpal is derived from the Greek meta, which

indicates “beyond,” “after,” or “accompanying,” and karpos,

which means “wrist.” Therefore, metacarpal denotes

“beyond or after the wrist.”

General Features

The five metacarpals are named for their associated digit,

that is, thumb metacarpal, index finger metacarpal, long

finger metacarpal, ring finger metacarpal, and small finger

metacarpal. Although the metacarpals often are indicated

by number (thumb as the first metacarpal, small finger as

the fifth metacarpal), confusion has arisen as to which is the

first and which is the fifth. Therefore, identifying each by

associated digit is preferable.

Despite their small size, the metacarpals are true long

bones (4,5) (Figs. 1.37 to 1.39; see Figs. 1.25 to 1.27A).

1 Skeletal Anatomy 63

FIGURE 1.37. Bones of right hand, palmar aspect,

showing muscle origins (red) and insertions (blue).

Each has an expanded proximal base, an elongated diaphysis (shaft or body), and a distal head. The head and bases

consist internally of cancellous bone, similar to other long

bones. The shaft has a thickened cortex that gradually thins

at the diaphyseal–metaphyseal junction. A medullary canal

lies in the shaft.

Variation exists as to the relative lengths of the

metacarpals (125,126). The long finger metacarpal usually

appears as the longest, although the index finger metacarpal

often is the longest or of equal length to the long finger

metacarpal (125,126). The metacarpal of the ring finger

usually is shorter than that of the index finger. The small

finger metacarpal usually is the shortest. The metacarpal of

the ring and little finger may be unproportionately shorter

than those of the index and long fingers, resulting in an

asymmetry to the hand (125,126). With a clenched fist, the

metacarpal head of the long finger often appears to be the

most prominent. This is due in part to its greater length,

64 Systems Anatomy

FIGURE 1.38. Bones of right hand, dorsal aspect,

showing muscle origins (red) and insertions (blue).

FIGURE 1.39. Right thumb metacarpal. A: Lateral (radial)

aspect. B: Medial (ulnar) aspect.

A B

but also to the relatively “shorter” position of the index

metacarpal, which is recessed into the carpus slightly more

than the long finger metacarpal. This results in the long finger metacarpal appearing longer clinically. Posner and

Kaplan have described the relative length relationships in

terms of ratio of metacarpal size to the corresponding phalanges (125) (Table 1.3). The relative lengths of the proximal

phalanges compared with the corresponding metacarpals are

as follows: index, 1:1.6 to 2.4; long, 1:1.4; ring 1:1.3 to 1.5;

little, 1:1.7 (125,126).

The base of each metacarpal flares from the shaft into a

wide proximal end. The flared base is cuboidal, wider dorsally than palmarly.

The shafts of the metacarpals are curved longitudinally,

with a slight convexity dorsally and concavity palmarly. The

radial and ulnar aspects of the shafts also are curved in a

slight concavity, presenting a surface for attachment of the

interosseous muscles. On the palmar surface of the shaft is

a prominent ridge that separates the attachments of adjacent palmar interosseous muscles. The dorsal surface is flattened and somewhat triangular, with the apex proximal.

The flattened dorsal surface allows easy gliding of the overlying extrinsic extensor tendons. The triangular outline

forms a ridge that runs along the dorsal aspect of the

metacarpal, separating two sloping surfaces that provide

attachments for the dorsal interosseous muscles.

The head of each metacarpal is slightly thicker in the

dorsopalmar direction. The articular surface of each head is

smooth, oblong, convex, and flattened from side to side.

On the radial and ulnar aspects of each head, at the level of

the dorsal surface, there is a tubercle that provides purchase

for a portion of the collateral ligaments. Between the tubercles on the palmar side, there is a hollow fossa for the

attachment of a portion of the collateral ligament of the

metacarpophalangeal joint and for the joint capsule. The

dorsal surface of the head is broad and flat and accommodates the overlying extrinsic extensor tendon. The palmar

aspect of the head contains a groove lying along the junction of the articular surface and the nonarticular portion of

the head. The extrinsic flexor tendons pass through the

groove, which helps form part of the fibroosseous tunnel of

the flexor sheath.

The articular surfaces are convex from dorsal to palmar

and from radial to ulnar, although there is less convexity

transversely. The metacarpal heads articulate with the proximal phalanges distally and the bases articulate with the distal

carpal row. The bases of the metacarpals also articulate with

each other (with the exception of the thumb metacarpal).

The metacarpals to the index, long, ring, and small finger

converge proximally. The thumb metacarpal, relative to the

other metacarpals, is positioned more anteriorly and rotated

medially on its axis through approximately 90 degrees, so

that its morphologic dorsal surface faces laterally and its morphologic palmar surface faces medially. This rotation of the

thumb allows it to flex medially across the palm so that it can

be rotated into opposition with each finger. The motion of

opposition consists of flexion and medial rotation (pronation) of the thumb across the palm, so that the pulp of the

thumb faces the pulp of the lesser digits.

The metacarpals can be associated with several sesamoid

bones. In general, a sesamoid is a bone that develops in a

tendon and occurs near a joint. By its location, the

sesamoid serves to increase the functional efficiency of the

joint by improving the angle of approach of the tendon into

its insertion (25). Sesamoids are variably present. They are

most common at the metacarpophalangeal joint of the

thumb, in the intrinsic tendons that flex the metacarpophalangeal joint. Sesamoids also often are present at the

metacarpophalangeal joint of the index and small finger,

and at the interphalangeal joint of the thumb. Occasionally,

one or two sesamoids may be present at any of the metacarpophalangeal joints of the hand (25). In addition to their

variable presence, a sesamoid may exist as a bipartite

sesamoid. They also may be fractured, resulting in two

small fragments with an irregular margin between them.

The metacarpals can be associated with several accessory

ossicles. In general, the development of these accessory

bones is from an additional or anomalous secondary ossification center, and therefore the accessory bones are

described later under sections on ossification. Accessory

bones, however, also can occur from other causes such as

trauma (46) or heterotopic ossification of synovial tags (47).

Therefore, anomalous, irregular ossicles or ossicles of

abnormal size or shape may be encountered that do not fit

a specific described accessory bone or location. The accessory bones located in the vicinity of the metacarpals, if present, usually are near the base, between the metacarpal and

adjacent carpal bone. They usually form from a secondary

ossification center of the carpal bone (46).

THUMB METACARPAL

(OSSA METACARPALIA I)

Ossification Centers and Accessory Bones

The thumb metacarpal has two ossification centers, one primary center in the midshaft and one secondary center in

1 Skeletal Anatomy 65

TABLE 1.3. RATIOS OF THE BONES OF THE

FINGERS

Distal Middle Proximal

Phalanx Phalanx Phalanx Metacarpal

Index 1 1.1–1.4 1.8–2.8 3.2–4.3

Middle 1 1.3–1.8 2.2–2.7 3.0–3.9

Ring 1 1.3–1.7 2.0–2.8 3.0–3.6

Small 1 1.0–1.2 1.6–2.2 2.7–3.9

From Posner MA, Kaplan EB. Osseous and ligamentous structures.

In: Spinner M, ed. Kaplan’s functional and surgical anatomy of the

hand, 3rd ed. Philadelphia: JB Lippincott, 1984:23–50.

the base (see Fig. 1.27A). This is in contrast to the remaining metacarpals, which have one primary ossification center

in the shaft and one secondary center in the head. Ossification in the midshaft begins in approximately the ninth

week of prenatal life. Ossification in the base begins late in

the second year in girls, and early in the third year in boys.

The ossification centers unite before the fifteenth year in

girls and before the seventeenth year in boys (127).

Several accessory bones can be associated with the

thumb metacarpal, usually located near or around the base

and in close proximity to the trapezium. These accessory

bones, if present, usually are the result of a secondary or

additional ossification center that does not fuse with the

associated bone. Those close to the thumb metacarpal usually are secondary ossification centers of the trapezium.

These accessory bones include the os trapezium secundarium (multangulum majus secundarium, carpometacarpale

II), the os praetrapezium (carpometacarpale I), and the os

paratrapezium (46) (see Fig. 1.27B). The os trapezium

secundarium is located between the ulnar base of the thumb

metacarpal and the distal margin of the trapezium. The os

praetrapezium is located between the thumb metacarpal (in

the mid-portion of the base) and distal aspect of the trapezium. The os paratrapezium is located between the radial

base of the thumb metacarpal and the distoradial aspect of

the trapezium (46) (see Fig. 1.27B).

Osteology of the Thumb Metacarpal

As emphasized by Williams [Gray’s Anatomy (5)], caution

needs to be exercised when describing the thumb

metacarpal because its position of rotation creates confusion in describing the various surfaces. Morphologic terms

are used, but are supplemented in places by their topographic equivalents. For instance, the dorsal (lateral) surface

of the thumb can be considered to face laterally; its long axis

diverges in a distal lateral direction from the carpus.

The thumb metacarpal is short and thick, and differs in

shape and configuration from the metacarpals of the digits

(see Figs. 1.25, 1.26, and 1.37 to 1.39). It is more stout, its

shaft is thicker and broader, and it diverges to a greater

degree from the carpus than the other metacarpals.

The metacarpal contains the widened base, a narrow

shaft, and a rounded head. The head and the base of the

thumb metacarpal internally consist of cancellous bone surrounded by a relatively thin cortical shell (see Fig. 1.39).

The shaft consists of thick cortical bone encircling the open

medullary canal. At the head and at the base, the medullary

canal rapidly changes to cancellous bone.

Base of the Thumb Metacarpal

The base of the thumb metacarpal differs greatly from all

the other metacarpals. The base flares into a wider trumpetshaped expansion, with a prominent palmar lip and thickening on the radial and ulnar borders. The articular surface

at the base, which appears concave when viewed from the

medial lateral direction and convex when viewed from the

anteroposterior direction, is saddle shaped to accommodate

the saddle shape of the trapezial articular surface. The base

of the thumb metacarpal articulates only with the trapezium. This complex joint surface configuration plays an

important role in the mechanism of opposition of the

thumb. It represents half of the saddle joint that it forms

with the corresponding surface of the trapezium (125). The

articular surface is demarcated from the shaft by a thick,

crestlike ridge that extends around the circumference,

clearly separating the articular surface from the shaft. On

the lateral (palmar) aspect of the base of the thumb

metacarpal lies the insertion area for the abductor pollicis

longus. There usually is a small tubercle at the lateral

metacarpal base for the insertion of this tendon. On the

ulnar aspect of the base lies the area of origin for the first

palmar interosseous muscle. This muscle origin may extend

distally to include a portion the ulnar aspect of the shaft.

There are no articular facets present on the sides of the

thumb metacarpal because this metacarpal does not articulate with any other metacarpal, in contrast to the remaining

metacarpals, each of which articulates at the base with its

adjacent metacarpal.

Shaft of the Thumb Metacarpal

The shaft of the thumb metacarpal is thick and broad. The

average thickness in the midshaft normally varies from 6 to

11 mm. The dorsal surface of the shaft is flat and wide, usually noticeably thicker and wider than the other

metacarpals. Its anteroposterior thickness is relatively less

pronounced, and in cross-section, the shaft is oval or somewhat triangular (apex palmar). It is mildly longitudinally

convex along its dorsal surface. It also is mildly longitudinally concave palmarly, radially, and ulnarly. The palmar

(medial) surface of the shaft is divided by a blunt ridge into

a larger lateral (anterior) part, which gives rise to the opponens pollicis muscle, and a smaller medial (posterior) part,

which gives origin to the lateral head of the first dorsal

interosseous muscle (see Figs. 1.37 and 1.38).

Head of the Thumb Metacarpal

The head of the thumb metacarpal is rounded but less convex than the other metacarpals. The head also is much less

spherical than the heads of the other metacarpals. It is thus

more suited for hingelike motion than it is for more universal joint motion (which is possible to a greater degree

with the other metacarpals). The articular surface is wide

and flat and has a quadrilateral appearance. The articular

surface extends much further palmarly than it does dorsally.

The head of the thumb metacarpal is thicker and broader

transversely. On the palmar aspect at the ulnar and radial

66 Systems Anatomy

angles, there are two articular eminences or tubercles which

articulate the thumb sesamoid bones. The lateral articular

eminence is larger than the medial. The associated sesamoid

bones lie within the two heads of the flexor pollicis brevis.

Associated Joints

The head of the thumb metacarpal articulates with the base

of the proximal thumb phalanx (Fig. 1.40; see Figs. 1.25,

1.26, and 1.37 to 1.39). The base of the thumb metacarpal

articulates with the trapezium. Unlike the remaining

metacarpals, the thumb metacarpal does not articulate with

its adjacent (index) metacarpal.

Muscle Origins and Insertions

Four muscles usually attach to the thumb metacarpal:

abductor pollicis longus, opponens pollicis, first dorsal

interosseous and, inconsistently, a small portion of the origin of the flexor pollicis brevis (most of which originates

from the palmar trapezium) (4,5) (see Figs. 1.37 and 1.38).

In addition, the adductor pollicis and flexor pollicis brevis

muscles insert into the closely associated thumb sesamoid

bones, located palmar (medially) to the head of the thumb

metacarpal.

The abductor pollicis longus inserts into a tubercle

located on the dorsal (lateral) aspect of the base of the

thumb metacarpal.

The opponens pollicis, which originates mainly from the

transverse carpal ligament as well as from the palmar trapezium, inserts into a long, oval area along the radiopalmar

aspect of the shaft of the thumb metacarpal.

The first dorsal interosseous muscle is a bipennate muscle

with two heads of origin, one on the thumb metacarpal and

one on the index finger metacarpal. On the thumb

metacarpal, the muscle has its origin along the dorsomedial

aspect of the shaft of the thumb metacarpal. (On the index

metacarpal, the second head originates along the radial aspect

of the shaft.) The first dorsal interosseous inserts on the radial

base of the proximal phalanx of the index finger and acts to

abduct the index finger at the metacarpophalangeal joint.

There is disagreement over the attachment of a first

palmar interosseous muscle to the thumb. Although there are

three distinct palmar (volar) interossei, some accounts

describe four palmar interossei (128). When four are

described, the first palmar interosseous consists of a small

group of muscle fibers that takes origin from the ulnar side

of the thumb metacarpal and blends with the oblique head

of the adductor pollicis to insert with it on the ulnar side of

the thumb. The continuity of this slip with the origin of the

1 Skeletal Anatomy 67

FIGURE 1.40. Frontal section through

articulations of the carpus.

adductor pollicis from the bases of the index and long finger metacarpals, and its insertion with the adductor pollicis,

seem to be sufficient reason for calling it a part of the

adductor pollicis rather than a first palmar interosseous.

Some authors have called this same slip the deep head of the

flexor pollicis brevis. Functionally, the entire adductor pollicis is similar to a palmar interosseous (4,5,128).

The origin of the flexor pollicis brevis usually is from the

transverse carpal ligament, as well as from the trapezoid

(deep head) and trapezium (superficial head). However,

there may be a small slip of fibers that originates from the

base of the thumb metacarpal on the palmar, medial aspect.

These fibers join the superficial belly and continue to insert

on the radial sesamoid (4).

Clinical Correlations: Thumb Metacarpal

The thumb metacarpal ossifies somewhat like a phalanx.

For this reason, the thumb skeleton has been considered to

consist of three phalanges. However, others have considered

the distal phalanx of the thumb to represent fused middle

and distal phalanges, a condition occasionally seen in the

fifth toe (129). When the thumb has three phalanges, the

metacarpal usually has a distal and proximal epiphysis. It

occasionally bifurcates distally, the ulnar portion having no

distal epiphysis and bearing two phalanges, and the radial

bifurcation showing a distal epiphysis and three phalanges

(130). The existence of only a distal metacarpal epiphysis

may be associated with a greater range of movement at the

metacarpophalangeal joint. In the thumb, it is the carpometacarpal joint that has the wider range, and a basal epiphysis in the first metacarpal may be attributable to this

(4,5). However, a distal epiphysis has been noted rarely in

the thumb metacarpal, and a proximal epiphysis has been

noted rarely in the index metacarpal (4,5).

In 1543, Vesalius originally suggested that the thumb

had three phalanges, considering the thumb metacarpal as

the proximal phalanx (4,5).

Sesamoid Bones

Sesamoid bones are common at the metacarpophalangeal

joints of the thumb and index and small fingers, and the

interphalangeal joint of the thumb. They may be mistaken

for fractures, and can themselves be fractured or develop as

bipartite sesamoids, further confusing the clinical impression. Schultz provides guidelines for distinguishing

sesamoids from fractures (25). Multipartite sesamoids usually are larger than a normal or fractured sesamoid. Multipartite sesamoids have smooth, more regular opposing surfaces with cortical margins, and may be bilateral. In an

acute fracture, the line of fracture is sharp, irregular,

assumes any shape, and may be displaced. At times, it may

be necessary to see fracture healing before the diagnosis can

be made (25,131–139).

Accessory Bones

Several accessory bones may be associated with the thumb

metacarpal and can be mistaken for fractures. An accessory

bone usually represents the residual of a secondary ossification center that does not fuse with the associated bone, but

it also may arise from trauma or heterotopic ossification of

synovial tags (46,47). The accessory bones associated with

the thumb metacarpal are usually in the region of the base,

representing secondary centers associated with the trapezium (see Fig. 1.27B). These accessory bones include the os

trapezium secundarium (located between the thumb

metacarpal and the distal ulnar corner of the trapezium),

the os praetrapezium (located between the central portion

of the base of the thumb metacarpal and the distal margin

of the trapezium), and the os paratrapezium (located

between the radial aspect of the base of the thumb

metacarpal and the distal radial corner of the trapezium

(46) (see Fig. 1.27B and descriptions earlier, under Ossification Centers and Accessory Bones).

INDEX FINGER METACARPAL

(OSSA METACARPALIA II)

Ossification Centers and Accessory Bones

The index metacarpal (second metacarpal) has two ossification centers, one primary center in the shaft and one secondary center in the head (see Fig. 1.27A). Ossification in

the midshaft begins in approximately the eighth or ninth

week of prenatal life. Ossification in the secondary head

center appears in the second year in girls, and between 1.5

to 2.5 years in boys. These secondary ossification centers

usually first appear in the index metacarpal, and sequentially appear in the order of long finger, ring finger, and,

last, the small finger. The secondary ossification in the head

of the index metacarpal unites with the shafts at approximately the fifteenth or sixteenth year in women, and the

eighteenth, nineteenth, or twentieth year in men (127).

Several accessory bones can be associated with the index

finger metacarpal, usually located at the base between the

metacarpal and the trapezoid. These accessory bones, if present, usually are the result of a secondary or additional ossification center that does not fuse with the associated bone.

Those associated with the index metacarpal usually are from

a secondary ossification center of the trapezoid. These

include the os trapezoideum secundarium (multangulum

minus secundarium), the os metastyloideum, and the os

parastyloideum (os carpometacarpale III) (see Fig. 1.27B)

(46). The os trapezoideum secundarium is located at the

radial base of the index metacarpal and the distal radial corner of the trapezoid. The os metastyloideum is located

between the ulnar base of the index finger metacarpal, the

distal ulnar corner of the trapezoid, and the distoradial corner of the capitate. The os parastyloideum is located

68 Systems Anatomy

between the ulnar base of the index metacarpal, the distoradial corner of the capitate, and the radial base of the

long finger metacarpal. It is located just radial to the site for

the os styloideum (which is associated with long finger

metacarpal; see Fig. 1.27B) (46).

Osteology of the Index Metacarpal

The index metacarpal often is the longest metacarpal and

usually has the largest base. It comprises a widened proximal base, a narrow curved shaft, and a rounded head (Fig.

1.41; see Figs. 1.25, 1.26, 1.37, and 1.38).

The head and base consist internally of cancellous bone

surrounded by a relatively thin cortical shell (see Fig. 1.41).

The shaft consists of thicker cortical bone that encircles the

open medullary canal. At the base and the neck, the

medullary canal rapidly changes to cancellous bone.

Base of the Index Finger Metacarpal

The base of the index metacarpal has a unique groove or

fork in the dorsopalmar direction. The fork is widened

proximally, slightly larger medially than laterally, and open

toward the carpus for articulation with the trapezoid. The

trapezoid thus is nestled securely by the base of the index

metacarpal. Medial to the groove in the base of the

metacarpal there is an extension of bone forming a ridge

that articulates with the capitate. On the lateral aspect of

the base, near the dorsal surface, is a quadrilateral facet for

articulation with the trapezium. Dorsal to the trapezial facet

is a roughened area for the insertion of the extensor carpi

radialis longus. On the palmar surface of the base is a small

tubercle or ridge that provides attachment for the insertion

of the flexor carpi radialis. The medial side of the base of the

index metacarpal is thickened, forming the larger half of the

metacarpal base. This portion articulates with the base of

long finger metacarpal through a prominent thickening, the

styloid process of the base of the long metacarpal (125,

126). This articulation includes a long facet, narrow in its

central area. The base of the index metacarpal thus includes

a total of four articular facets. The ulnar side of the base of

the index metacarpal, which articulates with the styloid

process of the long metacarpal, has a small, roughened area

just distal to the articular facet for insertion of strong

interosseous ligaments. These ligaments hold the base of the

index and long finger metacarpals together. There is a slight

depression between the two halves of the base of the

metacarpal that usually contains several small foramina for

nutrient arteries that arise from the dorsal carpal arch. Similar to the dorsal surface, the palmar surface of the

metacarpal has a roughened area with multiple foramina for

the palmar nutrient arteries entering the base (125).

Shaft of the Index Finger Metacarpal

The shaft of the index metacarpal is curved, convex dorsally

and concave palmarly. It has a flat, triangular dorsal surface

immediately proximal to the head. The shaft is oval or

slightly triangular in cross-section, flattened dorsally. The

dorsal surface is broad more distally, but proximally the

dorsal surface narrows to a ridge. The dorsal surface is lined

by lateral ridges that converge toward the dorsum, approximately at the junction of the distal two-thirds with the

proximal third, to form a single ridge running proximally

and ending at the apex of the forked base. The palmar surface of the shaft is smooth in the central area, but becomes

more irregular at the proximal and distal ends. The

metacarpal has converging borders that begin at the tubercles, one on each side of the head for the attachment of collateral ligaments. Along the shaft of the index metacarpal

three interosseous muscles originate, two dorsal

interosseous and one palmar interosseous. Proximally, the

lateral surface inclines dorsally for the ulnar head of the first

dorsal interosseous muscle. The medial surface inclines similarly, and is divided by a faint ridge into two areas: a palmar strip for origin of the first palmar interosseous and a

dorsal strip for the origin of the radial head of the second

dorsal interosseous muscle (2,4,5). At the junction of the

shaft and head, several small foramina usually are present

for the entrance of nutrient vessels.

Head of the Index Finger Metacarpal

The head of the index metacarpal is rounded and slightly

elongated in the dorsopalmar axis. Although the head may

1 Skeletal Anatomy 69

FIGURE 1.41. Right index finger metacarpal. A: Dorsolateral

aspect. B: Medial aspect.

A B

be irregular, it has a smooth convex area that extends further in the palmar–distal direction than in the mediolateral

direction. The extraarticular areas of the head are roughened and contain medial and lateral tubercles at the articular margins for attachment of the collateral ligaments and

joint capsule. The tubercles are located on the dorsal half of

the side of the metacarpal head. Along with the tubercles,

there is a slight elevated ridge that surrounds the articular

smooth area. The articular surface extends further over the

palmar aspect than over the dorsal aspect. There is a small

depression just proximal to the articular surface over the

mid-dorsal aspect of the head for the attachment of the capsule of the metacarpophalangeal joint. On the medial and

lateral surface of the metacarpal head are longitudinal furrows just proximal to the articular margin to assist the passage of the tendons of the interosseous muscles. At the margin of the articular surface, there are multiple small vascular

foramina in which vessels from the attaching soft tissues

enter the head.

Associated Joints

The base of the index metacarpal articulates largely with the

trapezoid, which lies in the groove at the metacarpal base

(see Figs. 1.25, 1.26, 1.37, 1.38, 1.40, and 1.41). In addition, the ulnar aspect of the base of the metacarpal contains

a small articular surface for articulation with the capitate,

and a more distal and ulnar articulation with the neighboring long finger metacarpal. On the radial aspect of the base

of the index metacarpal, there also is a small articular surface for articulation with the trapezium. The index

metacarpal usually does not articulate with the thumb

metacarpal.

The head of the index metacarpal articulates with the

base of the proximal phalanx of the index finger.

Muscle Origins and Insertions

Six muscles attach to the index metacarpal: the flexor carpi

radialis, the extensor carpi radialis longus, the first and second dorsal interosseous muscles, the first palmar

interosseous muscle, and, often, a relatively small portion of

the origin of the adductor pollicis oblique head (see Figs.

1.37 and 1.38).

The flexor carpi radialis inserts into the palmar aspect of

the base of the index metacarpal. The insertion point usually is wide, encompassing most of the width of the base of

the index metacarpal.

The extensor carpi radialis longus inserts into the dorsal

aspect of the base of the index metacarpal. The insertion

point usually is slightly radial to the longitudinal midline of

the metacarpal (4).

The first dorsal interosseous muscle (ulnar head) originates from the radial aspect of the shaft of the index

metacarpal. This muscle belly joins the belly originating

from the ulnar aspect of the thumb metacarpal (radial

head), thus forming a bipennate muscle with a common

insertion. The first dorsal interosseous muscle inserts into

the radial aspect of the base of the proximal phalanx of the

index finger. Considerable variations exist as to the bone

versus soft tissue insertion of the interosseous muscles (into

either the proximal phalanx or the extensor aponeurosis). In

the index metacarpal, most, if not all fibers insert into bone

(140), whereas the remaining dorsal and palmar

interosseous muscles show variation as to bone versus extensor insertion. See discussions of individual muscles in

Chapter 2. Most of the bony insertion of the first dorsal

interosseous probably is functionally advantageous, whereas

the bony insertion of a strong first dorsal interosseous muscle helps stabilize the index finger during pinch and grasp,

resisting the force exerted by the thumb by producing reciprocal abduction of the proximal phalanx of the index finger.

The second dorsal interosseous muscle (radial head)

originates from the ulnar aspect of the shaft of the index

metacarpal. This muscle belly joins the belly originating

from the radial aspect of the shaft of the long finger

metacarpal (ulnar head), thus forming a bipennate muscle

with a common insertion. The second dorsal interosseous

then inserts into either the lateral base of the proximal phalanx of the long finger, or the extensor aponeurosis (approximately 60% bone, 40% extensor hood) (140).

The first palmar interosseous muscle originates from the

palmar aspect of the ulnar side of the index metacarpal

shaft. The first palmar interosseous muscle inserts into the

extensor aponeurosis or, to a variable degree, into the base

of the ulnar aspect of the proximal phalanx of the index finger. The palmar interosseous muscles function largely to

adduct and flex the proximal phalanx. Throughout the

extensor aponeurosis, the interosseous muscles also assist

with extension of the middle and distal phalanges.

A small portion of the adductor pollicis oblique head

may originate from the base of the index metacarpal. This

usually is in the proximal, ulnar corner of the metacarpal on

the palmar side. Most of the origin of the oblique head of

the adductor pollicis attaches to the capitate and to the base

of the long finger metacarpal.

Clinical Correlations: Index Finger

Metacarpal

The base of each metacarpal, including the index

metacarpal, is somewhat cuboid, wider dorsally than palmarly. This results in a slightly wedge-shaped bone, with

the apex palmar. With this configuration, subluxation or

dislocation of the base of the index metacarpal on the

trapezoid usually occurs in a dorsal direction. Palmar dislocation of the base of the index metacarpal is understandably rare, usually prevented by the wide dorsal portion of the base.

70 Systems Anatomy

Sesamoid Bones

Sesamoid bones are common at the metacarpophalangeal

joints of the thumb and the index and small fingers, and

the interphalangeal joint of the thumb. They may be mistaken for fractures, and can themselves be fractured or

develop as bipartite sesamoids, further confusing the clinical impression. Schultz provides guidelines for distinguishing sesamoids from fractures. Multipartite sesamoids

usually are larger than a normal or fractured sesamoid.

Multipartite sesamoids have smooth, more regular opposing surfaces with cortical margins, and may be bilateral. In

an acute fracture, the line of fracture is sharp, irregular,

assumes any shape, and may be displaced. At times, it may

be necessary to see fracture healing before the diagnosis

can be made (25).

Accessory Bones

Several accessory bones may be associated with the index

finger metacarpal and can be mistaken for fractures. An

accessory bone usually represents the residual of a secondary

ossification center that does not fuse with the associated

bone, but it also may arise from trauma or heterotopic ossification of synovial tags (46,47). The accessory bones associated with the index metacarpal usually are in the region of

the base, representing secondary ossification centers associated with the trapezoid (see Fig. 1.27B). These accessory

bones include the os trapezoideum secundarium (located at

the radial base of the index metacarpal and the distal radial

corner of the trapezoid), the os metastyloideum (located

between the ulnar base of the index finger metacarpal, the

distal ulnar corner of the trapezoid, and the distoradial corner of the capitate), and the os parastyloideum (located

between the ulnar base of the index metacarpal, the distoradial corner of the capitate, and the radial base of the

long finger metacarpal; see Fig. 1.27B) (46) (see descriptions earlier, under Ossification Centers and Accessory

Bones).

LONG FINGER METACARPAL

(OSSA METACARPALIA III)

Ossification Centers and Accessory Bones

The long finger metacarpal (third metacarpal) has two

ossification centers, a primary ossification center in the

shaft and a secondary center in the head (see Fig. 1.27A).

Ossification in the midshaft begins in approximately the

ninth week of prenatal life. Ossification in the secondary

center in the head appears in the second year in girls, and

from 1.5 to 2.5 years in boys. These secondary ossification

centers usually appear first in the index metacarpal, and

sequentially appear in the order of long finger, ring finger,

and, last, the small finger. The secondary ossification in

the head of the long finger metacarpal unites with the

shaft at approximately the fifteenth or sixteenth year in

women, and the eighteenth or nineteenth year in men

(127).

On the dorsal aspect of the long finger metacarpal there

is a raised, thickened protuberance of bone often referred to

as the styloid. This styloid process may have a separate ossification center, or form a separate ossicle (see later) (46,

127).

Several accessory bones can be associated with the long

finger metacarpal, usually located at the base between the

metacarpal and the trapezoid. These accessory bones, if present, usually are the result of a secondary or additional ossification center that does not fuse with the associated bone.

Those associated with the long finger metacarpal usually are

from a secondary ossification center of the base of the

metacarpal (from the ossification center of the styloid) or

from a secondary center of the capitate. These include the

os styloideum (os carpometacarpale IV), the os parastyloideum (os carpometacarpale III), the os subcapitatum, the

os capitatum secundarium (os carpometacarpale V), and

the os gruberi (os carpometacarpale VI) (see Fig. 1.27B)

(46). The os styloideum is located at the radial corner of the

base of the long metacarpal, between the bases of the long

and index metacarpal and the distal radial corner of the capitate. The os parastyloideum is located just radial to the site

of the os styloideum, at the radial corner of the base of the

long metacarpal, and between the base of the index

metacarpal and distal radial corner of the capitate. The os

subcapitatum is located proximal to the mid-portion of the

base of the long finger metacarpal, adjacent to the central

portion of the body of the capitate. The os capitatum

secundarium is located at the ulnar base of the long finger

metacarpal, between the metacarpal and the distoulnar corner of the capitate, and close to the hamate and base of the

ring finger metacarpal. The os gruberi is located just ulnar

to the site of the os capitatum secundarium, at the ulnar

corner of the base of the long finger metacarpal, between

the long and ring finger metacarpals, the distoulnar corner

of the capitate, and the distoradial corner of the body of the

hamate (46) (see Fig. 1.27B).

Osteology of the Long Finger Metacarpal

The long finger metacarpal usually is the second longest

metacarpal, second only to the index finger metacarpal (Fig.

1.42; see Figs. 1.25, 1.26, 1.37, and 1.38). Similar to the

other metacarpals, the long finger metacarpal consists of a

widened proximal base, a narrow curved shaft, and a

rounded head. The head and base are composed internally

of cancellous bone surrounded by a relatively thin cortical

shell (see Fig. 1.42). The shaft consists of thicker cortical

bone that encircles the open medullary canal. At the base

and at the neck, the medullary canal rapidly changes to cancellous bone.

1 Skeletal Anatomy 71

Base of the Long Finger Metacarpal

The base of the long metacarpal is unique in that it contains

the styloid process, a short, consistent projection that

extends proximally from the radial side of the dorsal surface

(125). The base of the long finger metacarpal articulates

largely with the capitate by a facet that is convex anteriorly

and dorsally concave, where it extends to the styloid process

on the lateral aspect of its base (see Fig. 1.42). Through the

styloid process, there also is a narrow articulation for the

index metacarpal base comprising a narrow, striplike facet,

constricted centrally and somewhat hourglass-shaped.

There also may be a small articulation with the trapezoid on

the radial base of the styloid. The articular and size relationships of the bases of the index and long metacarpals are

variable. When the styloid process of the long finger

metacarpal is short, the ulnar part of the base of the index

metacarpal may articulate with a small portion of the capitate. On the radial side of the base of the long metacarpal,

just distal to the articular surface for the index metacarpal

base, there is a rough area for insertion of the intermetacarpal interosseous ligament (125). The long finger

metacarpal base also has an articulation with the ring finger

metacarpal. It consists of two oval articular facets. The palmar facet may be absent; however, less frequently the two

facets may be connected proximally by a narrow bridge

(4,5). This double facet articulates with a similar double

facet on the radial side of the base of the ring finger

metacarpal. There usually is a rough, raised area between

the two facets, just distal or palmar to the articular surface.

This rough area serves for the attachment of the associated

interosseous intermetacarpal ligament. On the palmar surface of the base of the metacarpal, there may be a roughened

or raised area for a small portion of the insertion of the

flexor carpi radialis. (The major insertion point for the

flexor carpi radialis is at the palmar base of the index

metacarpal.) The dorsal surface of the base of the long finger metacarpal contains a roughened or slightly raised area

for insertion of the extensor carpi radialis brevis. The insertion point is slightly radial to the midline of the shaft of the

metacarpal. On the widened, rough areas on the dorsal and

palmar surfaces of the base of the index metacarpal, there

usually are several small foramina for the nutrient arteries.

On the palmar surface of the base, there also is a portion of

a long longitudinal crest that extends to the shaft. This crest

serves for the origin of the adductor pollicis, and joins a

similar crest or roughened area on the capitate, which also

provides attachment for the adductor pollicis.

Shaft of the Long Finger Metacarpal

The shaft of the long finger metacarpal is curved, convex

dorsally and concave palmarly. To a large degree, the long

metacarpal resembles the index metacarpal. In cross-section, the shaft of the long finger metacarpal is oval or triangular, with the apex palmar. The dorsal surface of the shaft

is smooth to allow passage of the extrinsic extensor tendons.

The dorsal surface is somewhat flat, and is triangular with

the apex proximal. The dorsal surface widens slightly from

proximal to dorsal. There are two faint longitudinal lateral

ridges that form the edges of this dorsal triangle and converge toward the proximal third of the dorsal surface. A single ridge continues proximally toward the base. The exten72 Systems Anatomy

FIGURE 1.42. Right long finger metacarpal. A: Lateral aspect.

B: Medial aspect.

A B

sor digitorum communis crosses close to the triangular portion of the dorsal surface. On its lateral surface, the ulnar

head of the second dorsal interosseous muscle originates.

This lateral surface is demarcated by the lateral ridges on

the dorsal surface. On the medial surface, the radial head of

the third dorsal interosseous muscle originates. At the junction of the shaft and head, several small foramina usually

are present for the entrance of nutrient vessels. There is no

consistent nutrient vessel in the shaft. The metacarpal

receives most of its vascularity from the base and from the

head and neck regions (125).

Head of the Long Finger Metacarpal

The head of the long finger metacarpal is similar to that of

the index metacarpal. It is rounded, and slightly elongated

in the dorsopalmar axis. In the anteroposterior plane, the

head is round, smooth, and convex, flatter on the medial

and lateral sides. The articular surface extends much more

palmarly than dorsally, thus providing for more flexion of

the proximal phalanx. The head is roughened medially and

laterally, with medial and lateral tubercles at the articular

margins for attachment of the collateral ligaments and joint

capsule. Palmar to the tubercles, on the medial and lateral

aspects of the head, there are grooves in which the tendons

of the interosseous muscles pass. On the palmar surface of

the head, just proximal to the articular margin, there are

two tubercles for the insertion of the palmar joint soft tissues. Also in this region, at the margin of the articular surface, the bone is rough, and there are multiple small vascular foramina for nutrient vessels.

Associated Joints

The base of the long finger metacarpal articulates largely

with the distal end of the capitate (see Figs. 1.25, 1.26, 1.37,

1.38, 1.40, and 1.42). In addition, on the lateral base of the

long finger metacarpal, there is a narrow, hourglass-shaped

articular surface for articulation with the base of the index

metacarpal. The styloid process may articulate with the

trapezoid. On the medial base of the long finger metacarpal,

there is a similar strip or pair of circular articular areas for

articulation with the base of the ring finger metacarpal.

Distally, the long finger metacarpal articulates with the

base of the proximal phalanx of the long finger.

Muscle Origins and Insertions

There are five major muscle attachments to the long finger

metacarpal. These include the extensor carpi radialis brevis,

the second and third dorsal interosseous muscles, the

oblique head of the adductor pollicis, and the transverse

head of the adductor pollicis (see Figs. 1.37 and 1.38). The

long finger metacarpal does not give origin to a palmar

interosseous muscle. (Because it lies in the midline of the

hand, it does not need a muscle to adduct it into this position.)

The long finger metacarpal also may receive attachments

from the insertion of the flexor carpi radialis (4,5). However, most of the insertion of the flexor carpi radialis is into

the base of the index finger metacarpal.

The extensor carpi radialis brevis tendon inserts into the

dorsal base of the long finger metacarpal. The point of

insertion usually is radial to the midline of the shaft of the

metacarpal (4).

The second dorsal interosseous muscle (ulnar head) originates along the shaft of the lateral border of the long finger

metacarpal. These fibers are joined by fibers of the second

interosseous that originate from the medial border of the

adjacent index finger metacarpal (radial head), thus forming a bipennate muscle. The second dorsal interosseous

then inserts into either the lateral base of the proximal phalanx of the long finger, or into the extensor aponeurosis

(approximately 60% bone, 40% extensor hood) (140).

The third dorsal interosseous muscle (radial head) originates along the shaft of the medial border of the long finger metacarpal. These fibers are joined by fibers of the

third dorsal interosseous that originate from the lateral

border of the ring finger metacarpal (ulnar head), thus

forming a bipennate muscle. The third dorsal interosseous

then inserts into either the medial base of the proximal

phalanx of the long finger, or into the extensor aponeurosis (approximately 6% into bone, 94% into extensor

aponeurosis) (140,141)

The oblique head of the adductor pollicis originates

largely from the palmar aspect of the base of the long finger

metacarpal. The remaining fibers of the oblique head originate from the palmar capitate or trapezoid. The fibers of

the oblique head of the adductor pollicis join the fibers

from the transverse head, and collectively insert into the

ulnar sesamoid.

The transverse head of the adductor pollicis originates

from the palmar shaft of the long finger metacarpal. These

fibers join the fibers of the oblique head, and insert into the

ulnar sesamoid of the thumb metacarpal.

The flexor carpi radialis may insert partially into the

radial aspect of the base of the long finger metacarpal. Most

of the insertion of this muscle, however, is into the base of

the index metacarpal.

Clinical Correlations: Long Finger

Metacarpal

The base of the long finger metacarpal is somewhat cuboid,

wider dorsally than palmarly. This results in a slightly

wedge-shaped bone, with the apex palmar. The styloid

process at the base of the metacarpal adds to the width dorsally. With this configuration, subluxation or dislocation of

the base of the long finger metacarpal on the capitate usually occurs in a dorsal direction. Palmar dislocation of the

1 Skeletal Anatomy 73

base of the long finger metacarpal is understandably rare,

usually prevented by the wide dorsal portion of the base.

Accessory Bones

Several accessory bones may be associated with the long

finger metacarpal and can be mistaken for fractures. An

accessory bone usually represents the residual of a secondary ossification center that does not fuse with the associated bone, but it also may arise from trauma or heterotopic ossification of synovial tags (46,47). The accessory

bones associated with the long finger metacarpal usually

are in the region of the base, representing secondary ossification centers of the styloid of the metacarpal, or arise

from a secondary center of the capitate (see Fig. 1.27B).

These accessory bones include the os styloideum (located

at the radial corner of the base of the long metacarpal,

between the bases of the long and index metacarpal and the

distal radial corner of the capitate), the os parastyloideum

(located just radial to the site of the os styloideum, at the

radial corner of the base of the long metacarpal, and

between the base of the index metacarpal and distal radial

corner of the capitate), the os subcapitatum (located proximal to the mid-portion of the base of the long finger

metacarpal, adjacent to the central portion of the body of

the capitate), the os capitatum secundarium (located at the

ulnar base of the long finger metacarpal, between the

metacarpal and the distoulnar corner of the capitate, and

close to the hamate and base of the ring finger metacarpal),

and the os gruberi (located just ulnar to the site of the os

capitatum secundarium, at the ulnar corner of the base of

the long finger metacarpal, between the long and ring finger metacarpals, the distoulnar corner of the capitate, and

the distoradial corner of the body of the hamate; see Fig.

1.27B) (46) (see descriptions earlier, under Ossification

Centers and Accessory Bones).

RING FINGER METACARPAL

(OSSA METACARPALIA IV)

Ossification Centers and Accessory Bones

The ring finger metacarpal (fourth metacarpal) has two

ossification centers, a primary ossification center in the

shaft and a secondary center in the head (see Fig. 1.27A).

Ossification in the midshaft begins in approximately the

ninth week of prenatal life. Ossification in the secondary

center of the head appears in the second year in girls, and

from 1.5 to 2.5 years in boys. These secondary ossification

centers usually first appear in the index metacarpal, and

sequentially appear in the order of long finger, ring finger,

and, last, the small finger. The secondary ossification in the

head of the ring finger metacarpal unites with the shaft at

approximately the fifteenth or sixteenth year in women, and

the eighteenth or nineteenth year in men (127).

Several accessory bones can be associated with the ring

finger metacarpal, usually located at the base between the

metacarpal and the hamate or capitate. These accessory

bones, if present, usually are the result of a secondary or

additional ossification center that does not fuse with the

associated bone. Those associated with the ring finger

metacarpal usually are from a secondary ossification center

of the neighboring hamate or capitate, or from a secondary

ossification center in the styloid of the base of the adjacent

long finger metacarpal. These accessory bones include the

os gruberi (carpometacarpale VI), the os capitatum secundarium (carpometacarpale V), and the os hamuli proprium.

The os gruberi is located at the radial corner of the base of

the ring finger metacarpal, between the base of the long

metacarpal and distoulnar corner of the capitate. The os

capitatum secundarium is located just radial to the site of

the os gruberi, between the radial corner of the base of the

ring finger metacarpal and the proximal ulnar corner of the

long finger metacarpal (between the distal margins of the

capitate and hamate). The os hamuli proprium is associated

more closely with the hamate, proximal to the base of the

ring finger metacarpal (46) (see Fig. 1.27B).

Osteology of the Ring Finger Metacarpal

The ring finger metacarpal is intermediate in size between

the long finger and small finger metacarpals, and noticeably

shorter and thinner than the index and long metacarpals

(Fig. 1.43; see Figs. 1.25, 1.26, 1.37, and 1.38). It is similar in overall shape to the other metacarpals, containing a

widened proximal base, a narrower curved shaft, and a

rounded head. It most resembles the long finger metacarpal,

especially in the head and shaft; however, the base shows

distinct differences (see later). Internally, it also is similar to

the remaining metacarpals. The head and base consist internally of cancellous bone surrounded by a relatively thin cortical shell (see Fig. 1.43). The shaft consists of thicker cortical bone that encircles the open medullary canal. At the

base and at the neck, the medullary canal rapidly changes to

cancellous bone (127).

Base of the Ring Finger Metacarpal

The base of the ring finger metacarpal is relatively small and

quadrilateral, usually containing two proximal articular

facets and articular surfaces on the radial and ulnar aspects

of the base for the adjacent metacarpals.

There is considerable variation in the shape of the base

of the ring finger metacarpal, and it has been described in

several ways (see Anomalies and Variations, later) (81,94,

108,117,118,142). The proximal articular surface is quadrangular, is directed somewhat medially, and is convex anteriorly and dorsally concave. There is a proximal elevation on

the dorsal surface that divides the articular surface into

radial and ulnar parts, or facets. The radial facet of the ring

74 Systems Anatomy

finger metacarpal articulates with the ulnar third of the distal articular surface of the capitate. The ulnar facet of the

metacarpal articulates with the radial facet of the hamate.

The metacarpal’s articular portion for the capitate usually

involves only a small oval or square facet. Also on the radial

aspect of the base of the ring finger metacarpal, there is a set

of two oval or round facets for articulation with the adjacent long finger metacarpal base. On the ulnar side of the

base of the ring finger metacarpal, there is an oval, or narrow, oblong facet, usually with a concave surface, for articulation with the adjacent base of the small finger

metacarpal. The roughened area between the two proximal

articular facets provides an area of attachment for the

interosseous intermetacarpal ligament. On the base of the

metacarpal, on the dorsal and palmar surfaces just distal to

the articular margin, there are multiple small foramina for

nutrient vessels (5,125).

Shaft of the Ring Finger Metacarpal

The shaft of the ring finger metacarpal is slender and

curved. It is convex dorsally and concave palmarly. To a

large degree, the ring finger metacarpal shaft resembles that

of the index and long finger metacarpals, although it is

noticeably shorter and thinner. The metacarpal may taper

proximally, so that the narrowest portion is at the junction

of the base and the shaft. In cross-section, the metacarpal is

round, oval, or slightly triangular (apex palmar). On the

medial aspect of the shaft is a slight concavity for the origin

of the radial head of the fourth dorsal interosseous muscles.

On the lateral aspect, there is a slight concavity for the origin of the ulnar head of the third dorsal interosseous muscle. On the lateral surface of the shaft of the ring finger

metacarpal there is a faint ridge that separates the attachments of the second palmar interosseous muscle from the

ulnar head of the third dorsal interosseous muscles. The

dorsal surface of the shaft is smooth and somewhat flat to

allow passage of the extrinsic extensor tendons. The triangular flattened area present on the index and long

metacarpals also is present on the ring finger metacarpal.

The palmar surface, which is concave, is slightly flatter in

the proximal half. Along the distal half of the palmar surface, the surface tends to form a slight longitudinal ridge

along the midline of the cortical surface. There is no consistent nutrient vasculature in the shaft of the metacarpals.

The metacarpals receive most of their vascularity from the

base and the head and neck regions (125).

Head of the Ring Finger Metacarpal

The head of the ring finger metacarpal is similar to that of

the index and long metacarpals. It is round, but slightly

elongated in the dorsopalmar axis. The head is roughened

medially and laterally, with medial and lateral tubercles at

the articular margins for attachment of the collateral ligaments and joint capsule. At the margin of the articular surface, there are multiple small vascular foramina through

which vessels from the attaching soft tissues enter the head.

Anomalies and Variations in Morphology

of the Ring Metacarpal

Recent studies on the carpometacarpal joints have shown

that the base of the ring finger metacarpal has considerable

variation in morphology (81,94,108,117,142–145). The

general shape of the base, noted to be relatively flat or conical, usually is readily identifiable on standard radiographs

(117). With regard to articular morphology, the base of the

1 Skeletal Anatomy 75

FIGURE 1.43. Right ring finger metacarpal. A: Lateral aspect.

B: Medial aspect.

A B

ring finger metacarpal articulates with the hamate and, to a

variable degree, with the capitate (81,118,142,143,

146–148). The base of the ring finger metacarpal and the

associated articulations appear to exhibit more variation

than any of the other carpometacarpal joints (118). Five

different types of ring finger metacarpal base have been

described with regard to shape and articular configurations.

n Type I contains a broad base that articulates with the

hamate and has a single dorsal facet extension that articulates with the capitate. This type was present in approximately 39% of wrists.

n Type II contains a broad base that articulates with the

hamate, and two facet extensions (one dorsal and one

palmar) that articulate with the capitate. Type II was present in approximately 8% of wrists.

n Type III contains a relatively narrow base that articulates

only with the hamate. Type III was present in 9% of

specimens.

n Type IV contains a broad base that articulates with the

hamate and a separate, single dorsal facet that articulates

with the capitate. Type IV was present in approximately

34% of wrists.

n Type V contains a broad base that articulates with the

hamate and the capitate. Type V was present in approximately 9% of wrists (81,94,108,117).

Associated Joints

The base of the ring finger metacarpal articulates largely

with the distal end of the radial articular facet of the hamate

(see Figs. 1.25, 1.26, 1.37, 1.38, 1.40, and 1.43) (Also see

Anomalies above). In addition, on the medial base of the

ring finger metacarpal, there is a narrow, oval or hourglassshaped articular surface for articulation with the base of the

small finger metacarpal. On the lateral base of the long finger metacarpal, there is a similar strip or pair of circular

articular areas for articulation with the base of the long finger metacarpal. On the lateral base of the ring finger

metacarpal, between the articular facets for the hamate and

the long finger metacarpal, there is a small oval articular

area for the capitate.

Distally, the ring finger metacarpal articulates with the

base of the proximal phalanx of the ring finger.

Muscle Origins and Insertions

There are three major muscle attachments to the ring finger

metacarpal. These include the origins of the third dorsal

interosseous (ulnar head), the origin of the fourth dorsal

interosseous (radial head), and the origin of the second palmar interosseous (see Figs. 1.37 and 1.38).

The third dorsal interosseous muscle (ulnar head) originates along the shaft of the lateral border of the ring finger

metacarpal. These fibers are joined by fibers of the third

dorsal interosseous that originate from the medial border of

the adjacent long finger metacarpal (radial head), thus

forming a bipennate muscle. The third dorsal interosseous

then inserts into the either the medial base of the proximal

phalanx of the long finger, or into the extensor aponeurosis

(approximately 6% bone, 96% extensor hood) (140).

The fourth dorsal interosseous muscle (radial head) originates along the shaft of the medial border of the ring finger

metacarpal. These fibers are joined by fibers of the fourth

dorsal interosseous that originate from the lateral border of

the small finger metacarpal (ulnar head), thus forming a

bipennate muscle. The fourth dorsal interosseous then

inserts into either the medial base of the proximal phalanx of

the ring finger, or into the extensor aponeurosis (approximately 40% bone, 60% extensor aponeurosis) (140,141).

The second palmar interosseous muscle originates from

the lateral palmar border of the shaft of the ring finger

metacarpal. The muscle inserts into the extensor aponeurosis of the ring finger, or into the radial side of the base of the

proximal phalanx of the ring finger.

Clinical Correlations: Ring Finger

Metacarpal

The joint surfaces at the base of the ring and small finger

metacarpals are saddle-shaped or flat, respectively, and are

not confined by the borders of the adjacent metacarpal

bases or carpal bones (as with the index and long

metacarpals). This allows, in part, the greater motion at the

carpometacarpal joints of the small and ring finger, compared with the relatively restricted motion of the carpometacarpal joints of the index and long fingers.

The base of each metacarpal, including that of the ring

finger, is somewhat cuboid, wider dorsally than palmarly.

This results in a slightly wedge-shaped bone, with the apex

palmar. With this configuration, subluxation or dislocation

of the base of the ring finger metacarpal on the hamate usually occurs in a dorsal direction. Palmar dislocation of the

base of the ring finger metacarpal is understandably rare,

usually prevented by the wide dorsal portion of the base.

Accessory Bones

Several accessory bones may be associated with the ring finger metacarpal and can be mistaken for fractures. An accessory bone usually represents the residual of a secondary ossification center that does not fuse with the associated bone,

but it also may arise from trauma or heterotopic ossification

of synovial tags (46,47). The accessory bones associated

with the ring finger metacarpal usually are in the region of

the base, representing secondary ossification centers from

the capitate, hamate or a secondary center of the base of the

metacarpal (46) (see Fig. 1.27B). These accessory bones

include the os gruberi (located at the radial corner of the

base of the ring finger metacarpal, between the base of the

76 Systems Anatomy

long finger metacarpal and distoradial corner of the hamate),

the os capitatum secundarium (located just radial to the site

of the os gruberi, between the radial corner of the base of

the ring finger metacarpal, the proximal ulnar corner of the

long finger metacarpal, and the distal margins of the capitate and hamate), and the os hamuli proprium (which is

more closely associated with the hamate, located proximal

to the base of the ring finger metacarpal; see Fig. 1.27B)

(46) (see descriptions earlier, under Ossification Centers

and Accessory Bones).

SMALL FINGER METACARPAL

(OSSA METACARPALIA V)

Ossification Centers and Accessory Bones

The small finger metacarpal (fifth metacarpal) has two ossification centers, a primary ossification center in the shaft

and a secondary center in the head (see Fig. 1.27A). Ossification in the midshaft begins in approximately the ninth

week of prenatal life. Ossification in the secondary center of

the head appears in the second year in girls, and from 1.5

to 2.5 years in boys. The secondary ossification centers usually appear last in the small finger metacarpal (usually

appearing first in the index metacarpal, and sequentially in

the long finger, ring finger, and, last, the small finger). The

secondary ossification in the head of the small finger

metacarpal unites with the shaft at approximately the fifteenth or sixteenth year in women, and the eighteenth or

nineteenth year in men (127).

An accessory bone can be associated with the small finger metacarpal, the os vesalianum manius (os vesalii, os carpometacarpale VIII). It usually is located at the ulnar base

of the metacarpal, distal to the ulnar aspect of the hamate.

An accessory bone, if present, usually is the result of a secondary or additional ossification center that does not fuse

with the associated bone. That associated with the small finger metacarpal may be from a secondary ossification center

of the base of the metacarpal or from a secondary center of

the hamate (46) (see Fig. 1.27B).

Osteology of the Small Finger Metacarpal

The small finger metacarpal usually is the thinnest and

smallest of the metacarpals, although the thumb

metacarpal, which is much thicker, may be shorter. The

overall shape of the small finger metacarpal is similar to that

of the other metacarpals, containing a widened proximal

base, a narrower curved shaft, and a rounded head (Fig.

1.44; see Figs. 1.25, 1.26, 1.37, and 1.38). It differs most in

the shape and characteristics of the base. Internally, the

small finger metacarpal is similar to the other metacarpals.

The head and base consist of cancellous bone surrounded

by a relatively thin cortical shell (see Fig. 1.44). The shaft

consists of thicker cortical bone that encircles the open

medullary canal. At the base and at the neck, the medullary

canal rapidly changes to cancellous bone (127).

Base of the Small Finger Metacarpal

The base of the small finger metacarpal is larger than that

of the ring finger, and slopes proximally and ulnarly. The

medial portion of the base is nonarticular and contains a

thickening of bone or a tubercle for insertion of the extensor carpi ulnaris. The lateral base of the small finger

metacarpal articulates with the ulnar facet of the distal

hamate. The articular surface on the metacarpal is transversely concave, and convex from palmar to dorsal. To some

degree, this articular surface, which is saddle-shaped, is not

unlike the articular surface of the base of the thumb

metacarpal. This configuration contributes to the relatively

greater motion at the hamate–small finger metacarpal joint

compared with the carpometacarpal joints of the index and

long finger rays. The overall area of the articular surface at

the base is oval or quadrangular and directed somewhat laterally. On the lateral aspect of the base of the small finger

metacarpal, there is an oval or narrow facet for articulation

with the ring finger metacarpal base.

Shaft of the Small Finger Metacarpal

The shaft of the small finger metacarpal is slender and

curved. It is convex dorsally and concave palmarly. To a

large degree, the small finger metacarpal shaft resembles

that of the other metacarpals, although it is noticeably

shorter and thinner. On the dorsal portion of the lateral

aspect, there is a slight concavity for the origin of the ulnar

head of the fourth dorsal interosseous. On the palmar portion of the lateral aspect, there is a slight concavity for the

1 Skeletal Anatomy 77

FIGURE 1.44. Right small finger metacarpal. A: Lateral aspect.

B: Medial aspect.

A B

origin of the third palmar interosseous muscle. On the

medial surface of the shaft of the small metacarpal, there

is a concavity for attachment of the opponens digiti minimi. The dorsal surface of the shaft of the small metacarpal

is smooth to allow passage of the extrinsic extensor tendons. The dorsal surface of the shaft may appear somewhat triangular, similar to the other metacarpal shafts.

The shaft of the small metacarpal may taper or become

somewhat constricted at the junction of the proximal shaft

with the base. This area may be the narrowest portion of

the metacarpal.

Head of the Small Metacarpal

The head of the small finger metacarpal is similar in shape

to that of the other metacarpals, although noticeably thinner and smaller. It is rounded, and slightly elongated in the

dorsopalmar axis. The head is roughened medially and laterally, with medial and lateral tubercles at the articular margins for attachment of the collateral ligaments and joint

capsule. At the margin of the articular surface, there are

multiple small vascular foramina through which vessels

from the attaching soft tissues enter the head.

Associated Joints

The base of the small finger metacarpal articulates largely

with the distal end of the hamate, through the ulnar distal

articular facet of the hamate. In addition, on the lateral base

of the small finger metacarpal, there is a narrow, oval or

hourglass-shaped articular surface for articulation with the

base of the ring finger metacarpal (see Figs. 1.25, 1.26,

1.37, 1.38, 1.40, and 1.44).

Distally, the small finger metacarpal articulates with the

base of the proximal phalanx of the small finger.

Muscle Origins and Insertions

There are three major muscle attachments to the small finger

metacarpal. These include the origins of the fourth dorsal

interosseous (ulnar head), and the insertion of the opponens

digiti minimi, and the origin of the third palmar interosseous

(see Figs. 1.37 and 1.38).

The fourth dorsal interosseous muscle (ulnar head) originates along the shaft of the lateral border of the small finger

metacarpal. These fibers are joined by fibers of the fourth

dorsal interosseous that originate from the medial border of

the ring finger metacarpal (radial head), thus forming a

bipennate muscle. The fourth dorsal interosseous then

inserts into either the medial base of the proximal phalanx of

the ring finger, or into the extensor aponeurosis (approximately 40% bone, 60% extensor aponeurosis) (140,141).

The third palmar interosseous muscle originates from

the lateral palmar border of the shaft of the small

metacarpal. The muscle inserts into the extensor aponeurosis of the small finger, or into the radial side of the base of

the proximal phalanx of the small finger.

The extensor carpi ulnaris tendon inserts into the dorsomedial base of the small finger metacarpal. There usually is

a thickening of bone or a small tubercle for insertion of the

tendon.

The opponens digiti minimi inserts into the medial border of the shaft of the small finger metacarpal.

Clinical Correlations: Small Finger

Metacarpal

The joint surfaces at the base of the small and ring finger

metacarpals are saddle-shaped and flat, respectively, and are

not confined by the borders of the adjacent metacarpal

bases or carpal bones (as are the index and long finger

metacarpals). This allows, in part, the greater motion at the

carpometacarpal joints of the small and ring finger, compared with the relatively restricted motion of the carpometacarpal joints of the index and long fingers.

The base of each metacarpal, including that of the small

finger, is cuboid, wider dorsally than palmarly. This results

in a somewhat wedge-shaped bone, with the apex palmar.

With this configuration, subluxation or dislocation of the

base of the small finger metacarpal on the hamate usually

occurs in a dorsal direction. Palmar dislocation of the base

of the small finger metacarpal is understandably rare, usually prevented by the wide dorsal portion of the base.

Sesamoid Bones

Sesamoid bones are common at the metacarpophalangeal

joints of the thumb and index and small fingers, and the

interphalangeal joint of the thumb. They may be mistaken

for fractures, and can themselves be fractured or develop as

bipartite sesamoids, further confusing the clinical impression. Schultz provides guidelines for distinguishing

sesamoids from fractures. Multipartite sesamoids usually are

larger than a normal or fractured sesamoid. Multipartite

sesamoids have smooth, more regular opposing surfaces

with cortical margins, and may be bilateral. In an acute

fracture, the line of fracture is sharp, irregular, assumes any

shape, and may be displaced. At times, it may be necessary

to see fracture healing before the diagnosis can be made

(25).

Accessory Bones

The os vesalianum manus (os vesalii, os carpometacarpale

VIII) is an accessory bone that may be located at the ulnar

base of the small finger metacarpal, distal and ulnar to the

hamate. If present, it can be mistaken for a fracture. An

accessory bone usually represents the residual of a secondary

ossification center that does not fuse with the associated

bone, but it also may arise from trauma or heterotopic ossi78 Systems Anatomy

fication of synovial tags (46,47) (see Fig. 1.27B and descriptions earlier, under Ossification Centers and Accessory

Bones).

PHALANGES

Derivation and Terminology

The word phalanx is derived from the Greek word for a line

or array of soldiers (1).

General Features

Each digit has three phalanges: proximal, middle, and distal. The thumb has two phalanges: proximal and distal. The

proximal and middle digital phalanges all share a similar

internal structure, whereas the distal phalanges are

markedly different (see later). The phalanges are true long

bones with a well defined medullary canal (Fig. 1.45; see

Figs. 1.25, 1.26, 1.27A, 1.37, and 1.38), and contain, from

proximal to distal, a base, shaft (diaphysis), neck, and head.

Each head consists of two condyles. The distal phalanx does

not have a true head, but instead terminates in the distal

tuft. At either end, the bone becomes wider to form the

base and head, with the cortex becoming thinner and the

internal portion being replaced with cancellous bone. In the

diaphysis, similar to other long bones, the cortex is thick,

and the medullary canal is open. The proximal phalanges

are the longest and largest, the distal the shortest and smallest. Collectively, the three phalanges of the middle finger

(long finger) are the longest, resulting in the middle finger

usually having the greatest length. The ring finger usually is

second in length, and the small finger usually is the shortest. The index finger usually is slightly shorter than the ring

finger, but may be equal to or longer than the ring finger

(125).

Each of the phalanges has two ossification centers (see

Fig. 1.27A). The primary center is located in the diaphysis

and the secondary center is in the proximal portion, in the

epiphysis. Ossification begins prenatally in the shafts at the

following periods: distal phalanges, eight or ninth week;

proximal phalanges, the tenth week; middle phalanges, the

eleventh week or later. The epiphyseal centers appear in the

proximal phalanges early in the second year in girls, and

later in the second year in boys. In the middle and distal

phalanges, the epiphyseal centers appear in the second year

in girls, and in the third or fourth year in boys. All of the

epiphyses unite approximately the fifteenth to sixteenth

year in women, and the seventeenth to eighteenth year in

men (5).

Because of the differences of the phalanges of the digits

and the thumb, their osteology is discussed separately from

that of the digital phalanges.

PROXIMAL PHALANX OF THE DIGITS

Ossification Centers

The proximal phalanx of each digit has two ossification

centers, one in the shaft and one in epiphysis at the base

(Table 1.4; see Fig. 1.27A). The primary ossification in the

shaft begins prenatally in approximately the tenth week.

The secondary ossification in the base appears early in the

second year in girls and later in the second year in boys.

The times of ossification of the secondary center of the

proximal phalanx vary slightly among the different digits, as

described in the following sections (149) (Table 1.4).

Ossification of Index Finger Proximal Phalanx

In the index finger proximal phalanx, the basal epiphysis

first appears in boys at 15 to 18 months of age and in girls

at the 9 to 13 months of age. The epiphysis fuses to the

shaft in boys between 16 and 17 years of age and in girls

between 14 and 15 years of age (149).

Ossification of Long Finger Proximal Phalanx

In the long finger proximal phalanx, the basal epiphysis first

appears in boys at 15 to 18 months of age and in girls at 9

1 Skeletal Anatomy 79

FIGURE 1.45. Illustration of digit showing metacarpophalangeal and interphalangeal joints, palmar aspect.

TABLE 1.4. APPEARANCE OF OSSIFICATION CENTERS IN THEIR NORMAL SEQUENCE AND DATES OF

COMPLETE OSSIFICATION AND FUSION ACCORDING TO W. GREULICH AND S. I. PYLE

Sex First Appearance (mos.) Adult Status (yrs.)

Capitate Male Birth–3 17–18

Female Birth–3 15–16

Hamate Male 3 14–15

Female 3 12–13

Distal epiphysis of radius Male 12–15 18–19

Female 9–15 17–18

Basal epiphysis of proximal phalanx middle finger Male 15–18 15–17

Female 9–12 14–16

Basal epiphysis of proximal phalanx index finger Male 15–18 16–17

Female 9–13 14–15

Basal epiphysis of proximal phalanx ring finger Male 15–18 16–17

Female 9–12 14–15

Capital epiphysis metacarpal index finger Male 15–20 16–17

Female 9–13 15

Basal epiphysis of distal phalanx of thumb Male 15–18 15–151/2

Female 12–15 13–131/2

Capital epiphysis of middle metacarpal Male 15–20 16–17

Female 9–13 15

Capital epiphysis of ring metacarpal Male 15–20 16–17

Female 9–12 14–15

Basal epiphysis of proximal phalanx little finger Male 18–24 16–17

Female 15–18 14–15

Basal epiphysis of middle phalanx middle finger Male 18–24 16–17

Female 15–18 14–15

Basal epiphysis of middle phalanx ring finger Male 18–24 17

Female 15–18 15

Capital epiphysis of metacarpal little finger Male 24–30 16–17

Female 15–17 14–15

Basal epiphysis of middle phalanx index finger Male 24–32 16–17

Female 15–18 14–15

Triquetrum Male 24–36 15–16

Female 18–25 15–16

Basal epiphysis of distal phalanx middle finger Male 18–24

Female 18–24

Basal epiphysis of distal phalanx ring finger Male 18–24

Female 18–24

Basal epiphysis of first metacarpal Male 24–32

Female 18–22

Basal epiphysis of proximal phalanx of thumb Male 24–32

Female 18–22

Basal epiphysis of distal phalanx little finger Male 36–42

Female 18–24

Basal epiphysis of distal phalanx index finger Male 36–42

Female 24–30

Basal epiphysis of middle phalanx of little finger Male 42–48

Female 24–32

Lunate Male 32–42

Female 30–36

Lunate Male 32–42

Female 30–36

Trapezium Male 31/2–5 yrs.

Female 36–50

Trapezoid Male 5–6 yrs.

Female 31/2–4 yrs., 2 mo.

Scaphoid Male 5–6 yrs., 4 mo.

Female 31/2–4 yrs., 4 mo.

Distal epiphysis of ulna Male 5 yrs., 3 mo.–6-10 yrs.

Female 51/2–61/2 yrs.

Pisiform Male 17–18

Female 16–17

Sesamoid of abductor pollicis Male 12–13

Female 11

From, Greulich WW, Pyle SI. Radiographic atlas of skeletal development of the hand and wrist, 2nd

ed. Stanford, Stanford University Press, 1959, with permission.

to 12 months of age. The epiphysis fuses to the shaft in boys

between 15 and 17 years of age and in girls between 14 and

16 years of age.

Ossification of Ring Finger Proximal Phalanx

In the ring finger proximal phalanx, the basal epiphysis first

appears in boys at 15 to 18 months of age and in girls at 9

to 12 months of age. The epiphysis fuses to the shaft in boys

between 16 and 17 years and in girls between 14 and 15

years of age.

Ossification of Small Finger Proximal Phalanx

In the small finger proximal phalanx, the basal epiphysis

first appears in boys at 18 to 24 months of age and in girls

at 15 to 18 months of age. The epiphysis fuses to the shaft

in boys between 16 and 17 years of age and in girls between

14 and 15 years of age.

Osteology of the Proximal Phalanx

The proximal phalanx consists of a base, shaft, and head.

The proximal phalanx of each digit is similar. The proximal

phalanx of the long finger usually is the longest, followed,

in decreasing order of size, by the ring, index, and small finger proximal phalanges. The thumb proximal phalanx,

described separately later, usually is approximately the

length of the small finger proximal phalanx, although the

thumb proximal phalanx is much thicker and wider.

Base of the Proximal Phalanx

The base of each phalanx flares out from the shaft. There is

a slight convexity to the dorsal surface of the base. The palmar base is concave, terminating in a thickened ridge or lip

that borders the palmar surface of the base at the joint. On

the palmar surface of the base of the proximal phalanges

there is a slight groove to accommodate passage of the flexor

tendons.

Shaft of the Proximal Phalanx

The shaft of each phalanx is smooth, convex dorsally, and

concave palmarly, and narrows slightly medially and laterally from proximal to distal, terminating in the narrow

neck. This tapering is more pronounced in the middle phalanx compared to the proximal phalanx. The shaft of the

proximal phalanx is oval in cross-section, with a slight

squaring on the volar aspect as the medial and lateral surfaces meet the palmar surface. The shaft of the phalanges

tapers from proximal to distal in both the frontal and sagittal sections, resulting in a narrow distal portion of the shaft.

This narrow portion, located just proximal to the head,

often is referred to as the neck.

Head of the Proximal Phalanx

The neck of each proximal phalanx widens abruptly to

form the head of the phalanx. The head consists of two

condyles. The articular surface has a slight depression seen

in the anteroposterior plane, demarcating the two condyles.

The articular surface extends further palmarly than dorsally

to allow the greater amount of flexion (and relatively limited extension). The articular surface is rounded, as noted

on the lateral projection. The head does not have the

marked increase in thickness in the anteroposterior direction, as is present in the heads of the metacarpals.

Associated Joints

The proximal phalanx articulates with the head of the associated metacarpal at each metacarpophalangeal joint, and

with the base of the associated middle phalanx at the proximal interphalangeal joint (Fig. 1.46; see Fig. 1.45).

The metacarpophalangeal joint is a multiaxial joint that

allows movement in the medial and lateral directions, as

well as slight rotation, because of the more spherical shape

of the metacarpal head and the concavity of the base of the

proximal phalanx. The joint is stabilized by the collateral

ligaments, accessory collateral ligaments, volar plate, joint

capsule, and intrinsic and extrinsic overlying tendons.

1 Skeletal Anatomy 81

FIGURE 1.46. Illustration of digit showing metacarpophalangeal and interphalangeal joints, lateral

aspect.

The proximal interphalangeal joints are stabilized by the

collateral ligaments, accessory collateral ligaments, volar

plate, joint capsule, and overlying intrinsic and extrinsic

tendons. It is a hinge joint, unlike the multiaxial metacarpophalangeal joint. Thus, the proximal interphalangeal

joint does not produce the medial and lateral motions or

the slight rotation of which the metacarpophalangeal joint

is capable. The condyles of the proximal phalanx are symmetric, adding to the stability (and lack of motion) in the

medial and lateral planes.

Muscle Origins and Insertions

Several muscles insert into the base of the proximal phalanges. The palmar interosseous muscles insert into the ulnar

base of the index proximal phalanx, and the radial bases of

the ring and small finger proximal phalanges. The flexor digiti minimi and abductor digiti minimi insert into the ulnar

base of the small finger proximal phalanx. The first dorsal

interosseous inserts, in part, to the radial base of the index

finger proximal phalanx. The second and third dorsal

interosseous muscles insert, in part, into the radial and ulnar

bases of the long finger proximal phalanx, respectively. The

fourth dorsal interosseous inserts, in part, into the ulnar base

of the ring finger proximal phalanx. The amount of insertion into bone versus that into the extensor mechanism

tends to decrease consecutively from the index, long, and

ring fingers. This mechanism is complex, and is described in

detail in Chapter 2 (26,141) (Figs. 1.37 and 1.38).

MIDDLE PHALANX OF THE DIGITS

Ossification Centers

The middle phalanx of each digit has two ossification centers,

one in the shaft and one in epiphysis at the base (see Fig.

1.27A and Table 1.4). The primary ossification in the shaft

begins prenatally in approximately the eleventh week or later.

The secondary ossification in the base appears early in the

second year in girls and in the third or fourth year in boys.

The times of ossification in the secondary center of the

middle phalanx vary slightly among the different digits, and

are described in the following sections (149) (Table 1.4).

Ossification of Index Finger Middle Phalanx

In the index finger middle phalanx, the basal epiphysis first

appears in boys at 24 to 32 months of age and in girls at 15

to 18 months of age. The epiphysis fuses to the shaft in boys

between 16 and 17 years of age and in girls between 14 and

15 years of age.

Ossification of Long Finger Middle Phalanx

In the long finger middle phalanx, the basal epiphysis first

appears in boys at 18 to 24 months of age and in girls at 15

to 18 months of age. The epiphysis fuses to the shaft in boys

between 16 and 17 years of age and in girls between 14 and

15 years of age.

Ossification of Ring Finger Middle Phalanx

In the ring finger middle phalanx, the basal epiphysis first

appears in boys at 18 to 24 months of age and in girls at 15

to 18 months of age. The epiphysis fuses to the shaft in boys

at approximately 17 years of age and in girls at approximately 15 years of age.

Ossification of Small Finger Middle Phalanx

In the small finger middle phalanx, the basal epiphysis first

appears in boys at 42 to 48 months of age and in girls at 24

to 32 months of age. The epiphysis fuses to the shaft in boys

between 16 and 17 years of age and in girls between 14 and

15 years of age.

Osteology of the Middle Phalanx

The middle phalanges of the digits are similar to each other.

Overall, the middle phalanges are shorter than their associated proximal phalanges. The length ratio between the

proximal and middle phalanges varies, even in the same

individual and in the same hand. In general, the ratio of

length of the proximal phalanx to length of the middle phalanx is between 2:1 and 1.3:1, regardless of finger (125)

(Table 1.3). The middle phalanx of the long finger usually

is the longest, the ring and index middle phalanges are similar (although either may be the longer), and the small finger middle phalanx usually is the shortest. Each phalanx has

a base, shaft, and head.

Although the general appearance of the middle phalanges

is similar to that of the proximal phalanges, distinct differences exist. The palmar aspect of the middle phalanx shaft is

not as concave as is the palmar aspect of the proximal phalanx. The lateral crests are thicker in the middle phalanx, and

tend to be wider and rougher, occupying the midpart of the

phalanx. The nutrient foramina may be more visible or more

numerous on the palmar aspect just proximal to the head. In

the middle phalanx, the dorsal aspect of the shaft is more narrow proximal to the head and widens to a steeper degree

toward the base. The dorsal aspect of the shaft is more convex, smooth, and more nearly round than is the dorsal aspect

of the proximal phalanx. The heads of the middle and proximal phalanx are similar in configuration (125).

Base of the Middle Phalanx

The base of each phalanx flares out from the shaft on the dorsal, medial, lateral, and palmar surfaces. On the dorsal aspect

of the base, there is a transverse ridge along the most proximal rim, separating the base from the articular surface. The

ridge is more accentuated in its mid-portion, forming a dor82 Systems Anatomy

sal lip that extends proximally over the joint. This elevated

mid-portion forms a tubercle that provides insertion for the

central slip of the extensor mechanism. On the lateropalmar

aspect of the base, there is a prominent tubercle that terminates in a ridge on the medial and lateral aspects of the base.

This tubercle provides insertion of the collateral ligaments.

Although the palmar base is concave or flat, it terminates in

a thickened ridge or lip on the midpoint that borders the palmar surface of the base at the joint. This tubercle is just distal to the articular surface of the base. Just distal to this tubercle are multiple small foramina for nutrient vessels. The

articular surface of the base is divided into facets, consisting

of two concave depressions for the two condyles of the head

of the proximal phalanx. The two articular facets are separated by a dorsopalmar articular crest that corresponds to the

intercondylar depression of the head of the proximal phalanx.

This crest extends toward the dorsal tubercle of the base dorsally, and toward the palmar tubercle on the base volarly

(125). The palmar tubercle of the base of the middle phalanx

forms a palmar prominence in relation to the shafts of the

middle and proximal phalanges, and provides mechanical

advantages for the function of the flexor digitorum superficialis (125). The presence of the nutrient foramina in the protected areas under the tendon insertion is functionally advantageous because this allows movement of the flexor tendons

without interfering with the entering vessels (125).

Shaft of the Middle Phalanx

The shaft of the middle phalanx is shorter than that of the

proximal phalanx (125) (Table 1.3). The middle phalanx

can be as much as half the length of the corresponding

proximal phalanx, with the ratio of length of the proximal

phalanx to length of the middle phalanx between 2:1 and

1.3:1 (125). The shaft of the middle phalanx is less convex

dorsally and less concave palmarly compared with the proximal phalanx. The proximal half of the middle phalanx is

wider in proportion to the distal half, compared with the

proximal phalanx. The radial and ulnar borders of the shaft

are concave, and when viewed from dorsally, the shaft has a

slight hourglass shape, with the narrowest portion located

slightly distal to the mid-portion. There are prominent

crests on the proximal half of the shaft on both the radial

and ulnar aspects. On the palmar aspect of the middle phalanx, along the radial and ulnar portions of the proximal

half, the cortex is rough for the insertion of the flexor digitorum superficialis. This rough area tends to blend with the

roughened proximal shaft and base, for attachment of the

volar plate and joint capsule. The narrow portion of the

shaft just proximal to the head of the middle phalanx often

is referred to as the neck.

Head of the Middle Phalanx

The head of the middle phalanx is similar to that of the

proximal phalanx, although much smaller. The head of

each phalanx widens abruptly from the neck of the shaft.

The head consists of two condyles. The articular surface

has a slight depression seen in the anteroposterior plane,

demarcating the two condyles. The articular surface

extends further palmarly than dorsally to allow the greater

amount of flexion (and relatively limited extension). The

articular surface is rounded, as noted on the lateral projection. The head does not increase in thickness in the

anteroposterior direction, as do the heads of the

metacarpals.

DISTAL PHALANX OF THE DIGITS

Ossification Centers

The distal phalanx of each digit has two ossification centers,

one in the shaft and one in the epiphysis at the base (see Fig.

1.27A and Table 1.4). The primary ossification in the shaft

begins prenatally in the eight or ninth week. The secondary

ossification in the base appears early in the second year in

girls and in the third or fourth year in boys.

The times of ossification of the secondary center of the

distal phalanx vary slightly among the different digits, and

are described in the following sections (149) (Table 1.4).

Ossification of Index Finger Distal Phalanx

In the index finger distal phalanx, the basal epiphysis first

appears in boys at 36 to 42 months of age and in girls at 24

to 30 months of age. The epiphysis usually fuses to the shaft

in boys between 17 and 18 years of age and in girls between

15 and 16 years of age.

Ossification of Long Finger Distal Phalanx

In the long finger distal phalanx, the basal epiphysis first

appears in boys at 18 to 24 months of age and in girls at 18

to 24 months of age. The epiphysis usually fuses to the shaft

in boys between 17 and 18 years of age and in girls between

15 and 16 years of age.

Ossification of Ring Finger Distal Phalanx

In the ring finger distal phalanx, the basal epiphysis first

appears in both boys and girls at 18 to 24 months of age.

The epiphysis usually fuses to the shaft in boys at approximately 17 to 18 years of age and in girls at approximately

15 to 16 years of age.

Ossification of Small Finger Distal Phalanx

In the small finger distal phalanx, the basal epiphysis first

appears in boys at 36 to 42 months of age and in girls at 18

to 24 months of age. The epiphysis usually fuses to the shaft

in boys between 17 and 18 years of age and in girls between

15 and 16 years of age.

1 Skeletal Anatomy 83

Osteology of the Distal Phalanx

The distal phalanges differ in size, shape, and contour

from the proximal and middle phalanges. Each has a base,

a shaft, and distal tuft. Although the base and, to some

degree, the shaft share similarities to the proximal and

middle phalanges, the tuft is quite different in size and

configuration.

When compared with each other, the distal phalanges

of the long and ring finger tend to be similar in length,

followed by the slightly smaller index distal phalanx, followed in turn by the shortest small finger distal phalanx.

In some individuals, the long finger distal phalanx may be

up to 2 mm longer than the others (125). All of the distal

phalanges are much shorter and thinner than the distal

phalanx of the thumb. The widths of all of the distal phalanges are similar, with the exception of the small finger,

which usually is thinner. In general, the shape and overall

outline of the base of the distal phalanges are similar to

those of the middle phalanges. The shaft of the distal phalanges differs slightly from those of the proximal and middle phalanges, with the distal phalanx containing a shaft

that is shorter, narrower, and straighter and lacking the

curved contours (convex dorsally) of the others. The distal phalanx terminates in the roughened distal tuft that is

wider than the shaft. The average length ratios of the middle phalanx to the distal phalanx (with the middle phalanx

used as a unit) are as follows: index, 1:0.6 to 1:0.9; long,

1:0.6 to 1:0.7; ring, 1.0.6 to 1:0.7; small 1:1 to 1:0.8

(125) (Table 1.3).

Base of the Distal Phalanx

The base of the distal phalanx usually has the same width

(or is slightly wider) than the adjacent head of the middle

phalanx. In general shape, it resembles the base of the middle phalanx, although much smaller. On the dorsal aspect,

the base flares out dorsally and centrally, creating a ridge

that separates the articular surface from the shaft. The dorsal base is roughened slightly and forms a raised area, the

dorsal tubercle. The dorsal tubercle provides the insertion

site of the extensor digitorum communis (and extensor

indicis proprius on the index distal phalanx). On the radial

and ulnar aspects of the base are bone prominences known

as the lateral tubercles. The lateral tubercles are roughened

and raised, and serve for the attachment of the collateral ligaments and joint capsule of the distal interphalangeal joint.

The lateral tubercles are most pronounced on the volar half

of the base. On the volar surface of the base, there is a palmar lip or ridge along the joint margin, known as the volar

tubercle (125). The surface of the palmar aspect of the base

is, however, somewhat flatter and rougher, and irregular.

This area provides the insertion site for the flexor digitorum

profundus. In this area, multiple small foramina are present

for passage of the nutrient vessels.

Shaft of the Distal Phalanx

The shafts of the distal phalanges are short and thin compared with the shafts of the middle and proximal phalanges.

The shafts also are much shorter and thinner than that of

distal phalanx of the thumb. The shaft is wide proximally

and becomes progressively thinner as the tuft is approached.

The narrowest portion of the shaft is just proximal to the

formation of the tuft. The dorsal surface of the shaft is

rounded and slightly convex, but much less so than that of

the middle and proximal phalanges. On the palmar surface,

the shaft is slightly concave, but to a lesser degree than in

the middle and proximal phalanges. The medial and lateral

surfaces are rounded, and the widest portion of the shaft is

slightly volar. On cross-section, the shaft of the distal phalanx thus is oval or slightly triangular, with the base on the

volar half of the shaft.

Tuft of the Distal Phalanx

The distal phalanges terminate in a roughened, wide portion known as the tuft. The tuft consists of a thicker ridge

of bone that is crescent-shaped and lines the distal portion

of the distal phalanx. The crest is symmetric when viewed

from the palmar or dorsal aspect. When viewed dorsally, the

tuft is a thicken margin along the distal aspect of the phalanx, usually a few millimeters thick. When viewed from

the palmar surface, the margin of the tuft is thicker and

extends more proximally. The medial and lateral portions of

the tuft on the volar surface extend a few millimeters more

proximal into the shaft than the central volar portion. This

thickened area thus forms a horseshoe shape, opened proximally. On the medial and lateral surfaces of the tuft, the

thickest portion extends obliquely, from proximal volar to

distal dorsal. Several small foramina are visible on the distal

tuft for entrance of nutrient vessels. These are most numerous on the palmar surface. The tuft provides for the attachment of the septa that help support, stabilize, and anchor

the pulp of the digit to the distal phalanx.

Associated Joints

The base of the distal phalanx articulates with the head of the

middle phalanx through the distal interphalangeal joint. The

distal interphalangeal joint is a hinge joint. The joint surface

of the base of the distal phalanx has two facets, medial and

lateral, which articulate with the corresponding medial and

lateral condyles of the head of the middle phalanx. The joint

is stabilized by the collateral ligaments, accessory collateral

ligaments, the volar plate, and extrinsic tendons of the flexor

digitorum profundus and extensor digitorum communis

(and extensor indicis proprius of the index finger).

Muscle Origins and Insertions

The flexor digitorum profundus inserts into the palmar surface of the base of the distal phalanx. The extensor digito84 Systems Anatomy

rum communis inserts into the dorsal surface of the base of

the distal phalanx. The extensor indicis proprius also inserts

into the dorsal surface of the base of the distal phalanx,

slightly ulnar to the extensor digitorum communis.

THUMB PROXIMAL PHALANX

Ossification Centers

The thumb proximal phalanx has two ossification centers: a

primary center in the shaft and a secondary center in the

epiphysis (at the base; see Fig. 1.27A and Table 1.4). Ossification begins prenatally in the shafts, usually in the tenth

week. Ossification in the epiphyseal center appears in the

mid-portion in the second year in girls (18 to 22 months of

age), and in the later months of the second year or in the

early months of the third in boys (24 to 32 months of age).

The epiphysis unites to the shaft at approximately the fifteenth to sixteenth year in girls and in the seventeenth to

eighteenth year in boys (5,149).

Osteology of the Thumb Proximal

Phalanx

The proximal phalanx of the thumb consists of a base,

shaft, and a head. Overall, the proximal phalanx resembles

the other proximal phalanges, but in general is shorter,

with a length approximately that of the proximal phalanx

of the small finger. It is thicker than that of the small finger.

Base of the Thumb Proximal Phalanx

The base of proximal phalanx of the thumb is similar to the

base of the proximal phalanges of the digits. The base flares

out from the shaft, more noticeably on the palmar surface

than dorsally. The dorsal surface of the base is flatter than

the palmar surface, and has a slight convexity. There also is

a slight crest or roughened area that separates the articular

surface from the shaft. This dorsal roughened area provides

the insertion site for the extensor pollicis brevis. The palmar

base is concave, terminating in a thickened ridge that borders the palmar surface of the base at the metacarpophalangeal joint. On the palmar surface of the base of the proximal phalanges there is a slight groove to accommodate the

flexor tendons. This groove is better delineated in the proximal phalanges of the digits compared with that of the

thumb. The articular surface at the base of the proximal

thumb phalanx differs slightly from those of the digital

proximal phalanges. In the thumb, the articular surface at

the base is flatter and less concave to accommodate the

articular surface of the head of the thumb metacarpal,

which tends to be flatter and less spherical than in the other

metacarpals.

Shaft of the Thumb Proximal Phalanx

The shaft of the proximal phalanx of the thumb is approximately the length of the proximal phalanx of the small finger (although it actually may be shorter). The shaft is relatively thick, especially in its proximal portion, compared

with the other proximal phalanges. The shaft is rounded

and smooth, and in cross-section it is round or oval, slightly

flatted palmarly, and, to a lesser degree, flattened dorsally.

The shaft does not have the lateral crests seen on the proximal phalanges of the digits. Very seldom can a small foramen for a nutrient vessel be identified on the shaft (125).

Head of the Thumb Proximal Phalanx

The head of the thumb proximal phalanx resembles the

head of the other proximal phalanges. The head is slightly

larger, with a wider articulating surface. The articular surface extends more palmarly, and when viewed in the lateral

projection, the articular surface appears symmetrically

rounded. (There is no increase in thickness in the anteroposterior direction, as is noted in the heads of the

metacarpals). It has a well defined margin separating the

articular surface from the palmar and dorsal surfaces of the

shaft. The head has two condyles, easily visualized in the

anteroposterior plane. The medial and lateral surfaces of the

head are flat and roughened to provide attachment for the

collateral ligaments and joint capsule. The flattened areas

laterally give the squared appearance of the head as seen on

the anteroposterior view. Several small foramina are located

just proximal to the articular surface, especially on the palmar surface, providing access for nutrient vessels.

Associated Joints

The proximal phalanx of the thumb articulates proximally

with the head of the thumb metacarpal at the thumb

metacarpophalangeal joint. The proximal phalanx of the

thumb articulates distally with the base of the thumb distal

phalanx. The thumb metacarpophalangeal joint is similar to

that of the other metacarpophalangeal joints; however,

because of the shape of the adjoining joint surfaces, the

joint is more hingelike instead of multiaxial, as in the others (125). The metacarpophalangeal joint of the thumb is

associated with two sesamoid bones located in the volar

plate or thenar tendons. The lateral sesamoid usually is

slightly larger than the medial sesamoid. The joint is stabilized by collateral ligaments, accessory collateral ligaments,

and joint capsule, along with the intrinsic muscles (flexor

pollicis brevis, abductor pollicis brevis, extensor pollicis

brevis, and adductor pollicis) and the overlying extrinsic

tendons (flexor pollicis longus and extensor pollicis longus).

The interphalangeal joint of the thumb is a hinge joint,

larger than the interphalangeal joints of the digits. It is

stabilized by the collateral ligaments, accessory collateral

1 Skeletal Anatomy 85

ligaments, volar plate, and overlying extrinsic tendons

(flexor pollicis longus and extensor pollicis longus).

Muscle Origins and Insertions

Several muscles insert into the base of the thumb proximal

phalanx. The extensor pollicis brevis inserts into the dorsal

surface of the base. The abductor pollicis brevis inserts into

the radial aspect of the base. The flexor pollicis brevis inserts

into the palmar base. The adductor pollicis inserts into the

ulnar aspect of the base.

THUMB DISTAL PHALANX

Ossification Centers

The thumb distal phalanx has two ossification centers: a

primary center in the shaft and a secondary center in the

epiphysis (at the base; see Fig. 1.27A and Table 1.4). Ossification begins prenatally in the shaft, usually in the eighth

or ninth week. Ossification in the epiphyseal center appears

in the second year in girls (12 to 15 months of age), and in

the later months of the second year in boys (15 to 18

months of age). The epiphysis unites to the shaft at approximately the thirteenth year in girls and in the fifteenth year

in boys (5,149).

Osteology of the Thumb Distal Phalanx

The distal phalanx of the thumb is markedly larger; it is

longer, thicker, and wider, than the distal phalanges of the

other digits. However, other than the size, the overall characteristics and osteology are similar to those of the other

distal phalanges. The distal phalanx of the thumb consists

of a base, shaft, and a tuft. The tuft occasionally is incorrectly referred to as the head.

Base of the Thumb Distal Phalanx

The base of the thumb distal phalanx is wide and thick,

with pronounced flaring medially and laterally. There is a

ridge along the dorsal, medial, and lateral surfaces, outlining the articular surface. The dorsal base is roughened and

has a thick crest just distal to the articular surface. The crest

is more elevated in the central portion and provides the

attachment site of the extensor pollicis longus. On the

medial and lateral surfaces of the base, there is pronounced

flaring. Each side has small, irregular tubercles for attachment of the collateral ligaments and joint capsule. These

tubercles are more accentuated in the thumb than in the

phalanges. The palmar surface of the base is flatter (or even

slightly concave) compared with the flared dorsal base.

With less flaring and a flatter surface, the palmar base joins

the shaft in a more gradual manner. The palmar surface is

rough for attachment of the flexor pollicis longus. The

articular surface at the base is divided by a slight midcrest

into two concave surfaces. These surfaces articulate with the

condyles of the head of the proximal phalanx. The base of

the thumb proximal phalanx has multiple small foramina

for nutrient vessels. These are most easily visualized on the

palmar surface.

Shaft of the Thumb Distal Phalanx

The shaft (and overall length) of the thumb distal phalanx

is longer and wider than those of the digits. The shaft is

rounded on the dorsal and lateral surfaces, and somewhat

flat or slightly convex on the palmar surface. On cross-section, the shaft is oval or hemispherical in shape, and appears

much flatter than in the other digits. Specific foramina for

nutrient vessels usually are not visualized on the shaft.

Tuft of the Thumb Distal Phalanx

The distal tuft is a thickened, widened distal tip that

expands abruptly from the shaft. On the anteroposterior

projection, the tuft is oval, triangular, or somewhat diamond-shaped. It contains a thickened rim along the distal,

medial, and lateral margins. The palmar surface of the tuft

is smoother and less pronounced, and blends with the shaft

in a gradual manner. The tuft is roughened to provide for

the attachments of the many septa that help support, stabilize, and anchor the pulp of the distal portion of the thumb.

Associated Joints

The distal phalanx of the thumb articulates with the head

of the proximal phalanx through the interphalangeal joint

of the thumb. The articular surface of the base of the distal

phalanx is divided into two concave surfaces that articulate

with the two corresponding condyles of the head of the

proximal phalanx. The joint is a uniaxial hinge joint, stabilized by two collateral ligaments, two accessory collateral

ligaments, a volar plate, and a joint capsule. The extrinsic

tendons of the extensor pollicis longus and flexor pollicis

longus move the joint, as well as adding stabilization.

Muscle Origins and Insertions

There are two muscle insertions on the thumb distal phalanx. The extensor pollicis longus inserts into the base of the

phalanx on the dorsal surface. The flexor pollicis longus

inserts into the base of the phalanx on the palmar surface.

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1 Skeletal Anatomy 91

2

MUSCLE ANATOMY

MICHAEL J. BOTTE

The following sections describe the anatomic features of

skeletal muscles of the upper extremity. Each is provided as

a reference for a specific muscle, and is not intended for the

purpose of planning operative approaches. A summary of

muscle origin, insertion, innervation, vascular supply, and

action is listed initially, followed by a general description of

the gross anatomic features, actions and biomechanical

aspects, variations and anomalies, and clinical implications

of the anatomy (1–14). At the end of this chapter are several appendices for further reference. Appendix 2.1 summarizes the general features of each muscle for muscle

comparison. Appendix 2.2 lists the skeletal muscles as to

extremity compartments, from the standpoint of compartment syndrome. Appendix 2.3 lists muscle difference index

values. These values are comparisons of the architectural

features of several muscles of the forearm. The architectural

difference index allows comparison of the relative differences (or similarities) of each skeletal muscle with regard to

design and function, based on architectural properties

(15).

DELTOID MUSCLE (DELTOIDEUS)

Derivation and Terminology. Deltoid is derived from the

Latin deltoides, which means “triangular in shape or form”

(1,2).

Origin. Lateral third of clavicle, acromion, and inferior

edge of spine of the scapula.

Insertion. Deltoid tuberosity of the lateral humerus.

Innervation. Axillary nerve (C5, C6). Occasionally, a

contribution from C4 also may be present in the axillary

nerve (3–8).

Vascular Supply. Acromial and deltoid branches of the

thoracoacromial artery; posterior and anterior circumflex

humeral arteries; subscapular artery, and deltoid branch of

the profunda brachii. The thoracoacromial, posterior and

anterior circumflex humeral arteries, and the subscapular

artery all arise from the axillary artery (3–11).

Principal Action. Abduction, forward flexion, and extension of the humerus.

Gross Anatomic Description: Deltoid

Muscle

The deltoid is a relatively thick, curved muscle in the shape

of an isosceles triangle, with the apex pointed inferiorly. It

occupies and comprises the deltoid muscle compartment of

the shoulder (Appendix 2.2). The deltoid surrounds the

humeral head and glenohumeral joint on all aspects except

medially and inferiorly, and, when viewed from above, the

muscle appears somewhat U-shaped, with the open portion

facing medially. The muscle has a broad origin, expanding

anteriorly from the lateral third of the anterior clavicle, laterally from the superolateral aspect of the acromion, and

posteriorly along the inferior edge of the spine of the

scapula (Fig. 2.1). Based on the origin, the muscle has three

subdivisions: a clavicular, acromial, and a (scapular) spinous

part. The clavicular and spinous parts consist of long muscle fiber bundles that coalesce laterally and inferiorly at the

insertion to help form a “V” or inverted triangle shape. At

the insertion, the fibers converge into a short, thick tendon

that attaches to the deltoid tuberosity of the lateral mid-diaphysis of the humerus (Fig. 2.2). The tendon of the deltoid

also may give off an expansion into the brachial deep fascia

that may reach the forearm. The anterior and posterior portions of the muscle converge directly into the insertion. The

mid-portion, from the acromion, however, is multipennate.

In this portion, four or five intramuscular septa or tendinous expansions descend superiorly from the lateral aspect

of the acromion. Similarly, from the inferior insertional

area, three septa or tendinous expansions ascend from the

insertion site. The septa from the acromion above run

obliquely and insert or interdigitate with the separate septa

from the insertion site below (3,4,11–14). In addition,

there is interdigitation of the tendons from the clavicular

and spinous portions. The septa are interconnected with

short muscle fibers that provide powerful traction. The

muscle fasciculi are large, and produce a coarse longitudinal

striation. The deltoid is responsible for creating the

rounded profile of the shoulder (9–13).

The deltoid muscle is innervated by the axillary nerve

(C5, C6), which leaves the posterior cord of the brac

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