The shoulder joint has the greatest range of motion of all joints and is actually comprised of 4 separate boney and musculotendinous joints (Figure 1). These joints work together to both attach the upper extremity to the thorax and provide a powerful and smooth mechanism for upper extremity motion. The range of motion present in the healthy shoulder joint is remarkable, (Figure 2) accomodating 180 degrees elevation (up and down movement) at the front, about 60 degrees of up and down movement at the back, and from 170 degrees of round-house swing when the arm is hanging at the side, to 180 degrees of round-house swing when the arm is held straight out to the side, to almost no round-house swing when the arm is fully extended overhead.

This level of movement is remarkable considering both the forces applied to the shoulder by activity and the minimal boney contact present in the joint. Not surprisingly, injuries to this joint are common in athletes, particularly in those who participate in sports in which additional shoulder stresses due to throwing or physical contact occur (baseball, tennis, swimming, golf, football) leading to either over-use or traumatic injuries, respectively.