The shoulder joint is the joint with greatest range of motion of any joint. Because of this wide range of motion, one is able to place a hand in many advantageous positions. But the wide range of motion is at the expense of stability. A lack of stability results in a joint that is loose with a tendency to dislocate (come out of its socket). The joint and the tendons about the joint are subjected to considerable wear and tear leading to degeneration of the joint surface giving rise to arthritis and tears in the supporting tendons (the tough fibrous tissue through which a muscle attaches to bone)

Anatomy

• The shoulder is made up of three bones, the scapula, clavicle and humerus
  1. The scapula (shoulder blade) lies on the back of the chest and has a triangular shape. The part of the scapula at the shoulder forms a shallow socket (joint depression), the glenoid. The glenoid is surrounded by a soft tissue called the labrum that acts to deepen the socket into which the head of the humerus fits (Figure 1A and 1B)
  2. The clavicle (collar bone) is a long narrow bone that bridges between the sternum (breastbone) and the shoulder
  3. The humerus is the bone of the upper arm that lies between the shoulder and the elbow. At the shoulder it has a rounded head that fits into the glenoid

Figure 1a - The scapula, humerus and clavicle are the three bones that make up the shoulder. As seen from the front	Figure 1b - As seen from the back