To understand the condition better it is helpful to know about the basic anatomy of shoulder joint. The shoulder joint is formed by three bones — the arm bone (humerus), shoulder blade (scapula), and the collar bone (clavicle). The rounded head of the arm bone (humerus) is relatively large compared to the socket of the shoulder blade and this size discrepancy allows for the large range of motion of the shoulder. The shoulder joint is surrounded by the strong joint capsule and further supported by a group of muscles called the rotator cuff.
