Anatomy

The shoulder is a ball and socket joint in the upper extremity. The glenoid (the socket) and the humeral head (ball) form the gleno-humeral joint. This joint is enclosed in a capsule. Surrounding the shoulder are the tendons of four muscles that are responsible for the initiation and modulation of shoulder movement – the rotator cuff. Around these are the larger muscles which are responsible for gross, powerful movements – the trapezius, deltoid, pectorals, rhomboids, latissimus dorsi, levator scapulae. Many of these muscles attach to the shoulder blade (scapula), or the socket part of the shoulder joint. Movement of the shoulder depends on the synchronous action of all these muscles.