Chapter Summary

Classification of Joints

1. Joints are formed as adjacent bones articulate. Arthrology is the science concerned with the study of joints; kinesiology is the study of movements involving certain joints.
2. Joints are classified as fibrous, cartilaginous, or synovial.

Fibrous Joints

1. Articulating bones in fibrous joints are tightly bound by fibrous connective tissue. Fibrous joints are of three types: sutures, syndesmoses, and gomphoses.
2. Sutures are found only in the skull; they are classified as serrate, lap, or plane.
3. Syndesmoses are found in the vertebral column, middle ear, antebrachium, and leg. The articulating bones of syndesmoses are held together by interosseous ligaments, which permit slight movement.
4. Gomphoses are found only in the skull, where the teeth are bound into their sockets by the periodontal ligaments.

Cartilaginous Joints

1. The fibrocartilage or hyaline cartilage of cartilaginous joints allows limited motion in response to twisting or compression. The two types of cartilaginous joints are symphyses and synchondroses.
2. The symphysis pubis and the joints formed by the intervertebral discs are examples of symphyses.
3. Some synchondroses are temporary joints formed in the growth plates between the diaphyses and epiphyses in the long bones of children. Other synchondroses are permanent; for example, the joints between the ribs and the costal cartilages of the rib cage.

Synovial Joints

1. The freely movable synovial joints are enclosed by joint capsules that contain synovial fluid. Synovial joints include gliding, hinge, pivot, condyloid, saddle, and ball-and-socket types.
2. Synovial joints contain a joint cavity, articular cartilages, and synovial membranes that produce the synovial fluid. Some also contain articular discs, accessory ligaments, and associated bursae.
3. The movement of a synovial joint is determined by the structure of the articulating bones, the strength and tautness of associated ligaments and tendons, and the arrangement and tension of the muscles that act on the joint.

Movements at Synovial Joints

1. Movements at synovial joints are produced by the contraction of the skeletal muscles that span the joints and attach to or near the bones forming the articulations. In these actions, the bones act as levers, the muscles provide the force, and the joints are the fulcra, or pivots.
2. Angular movements increase or decrease the joint angle produced by the articulating bones. Flexion decreases the joint angle on an anterior-posterior plane; extension increases the same joint angle. Abduction is the movement of a body part away from the main axis of the body; adduction is the movement of a body part toward the main axis of the body.
3. Circular movements can occur only where the rounded surface of one bone articulates with a corresponding depression on another bone. Rotation is the movement of a bone around its own axis. Circumduction is a conelike movement of a body part.
4. Special joint movements include inversion and eversion, protraction and retraction, and elevation and depression.
5. Synovial joints and their associated bones and muscles can be classified as first-, second-, or third-class levers. In a first-class lever, the fulcrum is positioned between the effort and the resistance. In a second-class lever, the resistance lies between the fulcrum and the effort. In a third-class lever, the effort is applied between the fulcrum and the resistance.

Specific Joints of the Body

1. The temporomandibular joint, a combined hinge and gliding joint, is of clinical importance because of temporomandibular joint (TMJ) syndrome.
2. The glenohumeral (shoulder) joint, a ball-and-socket joint, is vulnerable to dislocations from sudden jerks of the arm, especially in children before strong shoulder muscles have developed.
3. There are two sets of articulations at the elbow joint as the distal end of the humerus articulates with the proximal ends of the ulna and radius. It is a hinge joint that is subject to strain during certain sports.
4. The metacarpophalangeal joints (knuckles) are condyloid joints, and the interphalangeal joints (between adjacent phalanges) are hinge joints.
5. The ball-and-socket coxal (hip) joint is adapted for weight bearing. Its capsule is extremely strong and is reinforced by several ligaments.
6. The hinged tibiofemoral (knee) joint is the largest, most vulnerable joint in the body.
7. There are two hinged articulations within the talocrural (ankle) joint. Sprains are frequently associated with this joint.