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
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© 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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