Anatomy of the shoulder
The shoulder consists of three bones, the shoulder blade (scapula), the upper arm (humerus) and the collarbone (clavicle). The shoulder joint is formed by the glenoid (part of the shoulder blade) and the head of the upper arm. There is a joint capsule around the joint. It is surrounded by muscles and tendons. Together these muscles and tendons form the ‘cuff’. The rotator cuff, a complex of four tendons (subscapularis, supraspinatus, infraspinatus and teres minor), connects the upper arm to the shoulder blade. In normal circumstances there is enough space between the head of the upper arm and the acromion so that the rotator cuff that is found in between, can move with ease without rubbing against the acromion. The bursa in between ensures supple movement between all these structures.