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7 Articular System

Joints, simply defi ned, are the meeting

places between bones. Th is simple defi nition describes a joint as any place

in the skeleton where one skeletal element contacts another skeletal element. It is important to understand that, as a part of this defi nition,

the bones never contact each other directly. Instead, there is always some other connective tissue between the bony contact

surfaces. Joints come in a wide variety of structural junctions, with an accompanying variety of functions.

Because joints have various functions and those

functions do not always deal with movement, it is illogical to defi ne joints by their movements. Th e best

method for classifying joints is based on their structure. Because the structure of joints includes the connective tissues between the neighboring bones, a

classifi cation based on the structure of those tissues

is logical. At the simplest level, there are two basic

ways bones connect with one another to form joints.

Either they are connected by solid masses of connective tissue, or they are bound together by a connective

tissue capsule, which surrounds a lubricated cavity between the adjoining bones.

Joints formed by a solid core of connective

tissue between the neighboring bones are called

synarthroses. Th ere are two subcategories of

synarthroses — fi brous joints, which have connective tissue cores of connective tissue proper, typically dense irregular connective tissue, and cartilage

joints, which use some form of cartilage as the

connecting tissue between the bones. Th e capsular joints, with their lubricated cavity, are called

diarthroses or synovial joints. Th ere are numerous subcategories of diarthroses, each

based on the structure and function of their

articular surfaces.

In addition to joints, this chapter will

also illustrate other closely related synovial

structures — bursae and synovial (tendon)

sheaths.

Find more information

about arthrology in

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REAL ANATOMY

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tissue binding the neighboring bones can vary considerably. Examples of fi brous joints are depicted on this and the facing

page. Gomphoses and sutures (the four different suture types are shown on the opposite page) have a very thin membrane

of collagenous connective tissue anchoring neighboring bony structures to one another. On the other hand, the syndesmoses between the tibia and fi bula — both the interosseous membrane and the tibiofi bular ligaments at the distal end — have

considerably more binding connective tissue. There is also an example of another syndesmosis, the interspinous ligament,

in the next section.

Fibrous joints are synarthrotic joints that

bind bone to bone with collagenous connective tissue. The amount of connective

Synarthrosis - Fibrous Joints

 1 Periodontal membrane

 2 Crown of tooth

 3 Root of tooth

 4 Gingiva

 5 Mandible

 6 Tibia

 7 Fibula

 8 Interosseous membrane

 9 Anterior tibiofibular ligament of tibiofibular syndesmosis

10 Patellar ligament (cut)

Dento-alveolar syndesmosis or gomphosis

Sagittal section of tooth in mandible

Crural skeleton – tibia and fi bula

Anterior view

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Squamous-type suture

Squamous or temporoparietal suture

Denticulate-type suture

Lamboidal or parieto-occipital suture

Serrate-type suture

Coronal or frontoparietal suture

Plane-type suture

Internasal suture

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Sagittal section of head and trunk

Medial view

Synarthrosis - Cartilaginous Joints Like the fi brous joints, the

cartilaginous joints join

neighboring skeletal ele-

 1 Intervertebral disc (symphysis)

 2 Nucleus pulposus of intervertebral disc

 3 Anulus fibrosus of intervertebral disc

 4 Pubic symphysis

 5 Manubriosternal synchondrosis

 6 Spheno-occipital synchondrosis

 7 Epiphysial cartilage or primary cartilaginous joint

 8 Sternocostal (synchondrosis)

 9 Sternocostal (typically synovial but can be symphysial)

10 Interchondral (synovial)

 11 Interchondral (synchondrosis)

12 Costochondral (synchondrosis)

13 Interspinous ligament (vertebral syndesmosis)

14 Nuchal ligament (vertebral syndesmosis)

15 Anterior longitudinal ligament (vertebral syndesmosis)

16 Posterior longitudinal ligament (vertebral syndesmosis)

17 Body of vertebra

18 Spinous process of vertebra

19 Lamina of vertebra

20 Psoas major muscle

21 Aorta

22 Inferior vena cava

ments with a solid mass of connective tissue, but the uniting tissue is some type of cartilage instead of collagenous connective tissue proper. The three types of cartilaginous joints are: 1) synchondroses, 2) symphyses, and 3) epiphysial cartilages

or primary cartilaginous joints. The photos on these facing pages depict the different categories of cartilaginous joints. A few

syndesmoses from the fi brous joint category are also evident.

Transverse section of lumbar intervertebral disc

Inferior view

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Radiograph of juvenile wrist region

Anterior view

Joints of the thoracic cage

Anterior view

Epiphysial cartilage Fetal skeleton 200x

Posterior view

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Diarthroses or Synovial Joints Diarthroses differ from synarthroses

in one major way: instead of connecting neighboring bones by a solid mass

of connectve tissue, the bony connection consists of a double-layered connective tissue capsule that surrounds a lubricated

cavity between the bones. Within the capsule the ends of neighboring bony surfaces are covered by a smooth layer of hyaline cartilage. As a result of this design there is typically a much greater range of motion present in synovial joints, and they

form the joints of the skeleton that are responsible for the major movements of the body. The outer layer of the capsule, the

fi brous membrane, is continuous with the periosteum on the adjoining bones, while the inner layer of the capsule, the synovial membrane, attaches from the border of the articular cartilage on one bone to the border of the articular cartilage on the

other bone. Additionally, the synovial membrane secretes synovial fl uid, a lubricant that reduces friction between the mobile

cartilage-covered articular surfaces of the bones. The section through a fi nger joint below and the dissections of the knee

joint on the opposite page illustrate the basic features of a synovial joint. The pages that follow depict the major synovial

joints of the skeleton. One other key feature among synovial joints that is responsible for their varied range of motion is the

shape of the adjoining bone surfaces. It is this feature that anatomists use to describe the different types of synovial joints.

 1 Middle phalanx of index finger

 2 Proximal phalanx of index finger

 3 Fibrous membrane of joint capsule

 4 Synovial membrane of joint capsule

 5 Articular cartilage

 6 Joint cavity

 7 Collateral ligament

 8 Quadriceps tendon

 9 Patellar ligament

10 Suprapatellar bursa

 11 Synovial fold

12 Meniscus

13 Periosteum

14 Junction of periosteum (removed) with fibrous membrane

15 Junction of synovial membrane (removed) with articular cartilage

16 Femur with periosteum removed

17 Tibia with periosteum removed

18 Fibula with periosteum removed

19 Patella within quadriceps tendon

Proximal interphalangeal joint showing design of synovial joint

Frontal section, anterior view

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Dissection of knee showing design of synovial joint

Medial view

Dissection of knee showing design of synovial joint

Lateral view

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