SHOULDER JOINT

1. This ball and socket joint is the most mobile in the body, and consequently is the least stable and prone to dislocation, especially in children.

2. It is formed by the glenoid cavity of the scapula and the head of the humerus, and is well padded with protective bursae.

3. The capsular ligament is very loose inferiorly to allow for the free movement normally possible at this joint.

4. The glenoid cavity is deepened by a rim of fibrocartilage, the glenoidal labrum, which provides additional stability without limiting movement.

5. The tendon of the long head of the biceps muscle is held in the intertubercular (bicipital) groove of the humerus by the transverse humeral ligament.

6. It extends through the joint cavity and attaches to the upper rim of the glenoid cavity.

7. Synovial membrane forms a sleeve round the part of the tendon of the long head of the biceps muscles within the capsular ligament and covers the glenoidal labrum.

8. The joint is stabilized partly by a number of ligaments (the glenohumoral, coracohumeral and transverse humeral) but mainly by the muscles (and their tendons) present in the shoulder.

9. The stability of the joint may be reduced if these structures, together with the tendon of the biceps muscle, are stretched by repeated dislocations of the joint.

MUSCLES AND MOVEMENT.