25. Disorders of the shoulder

The shoulder consists of three bone fragments: the scapula, the clavicle and the humerus, surrounded by a joint capsule and a number of muscles providing stability and guiding movement (including the four muscles of the rotator cuff, the deltoid muscle and the pectoralis major muscle) (fig. 25.1). Typically, a relatively large sphere (humeral head) articulates on a small, almost flat contact surface (glenoid). As a result, a large freedom of movement exists, but also potential instability.