The shoulder is the only joint in the body that can accomplish a 360 degree rotation, although this level of mobility translates into a lesser degree of stability than other joints. The primary function of the shoulder is to support, or anchor, the different positions of the hand and arm. The bony structures of the shoulder include the scapula, humerus, and clavicle, which together create two separate joints — the glenohumeral joint and the acromioclavicular joint. Some of the muscles and tendons that support the shoulder joint are referred to as the rotator cuff.