Shoulder injuries are far too prevalent in many sports. These injuries tend to fall into two groups. The least common are those injuries caused by a sudden traumatic force, as seen with the football player being tackled and landing oddly, causing a dislocation or separation of the shoulder.
The more common injury type is the overuse injury that occurs in athletes who are involved in weightlifting, throwing, swimming, swinging clubs or racquets. The majority of these injuries are preventable with a program of specific shoulder exercises and an understanding of the workings of the shoulder joint.
The shoulder is the most mobile joint in the body. The shoulder joint looks like a golf ball sitting on a tee. The humeral head (ball) sits in the glenoid (socket) which is shaped like a shallow dish. A circular structure of soft tissue, the labrum, deepens the dish. The stability of the shoulder joint is provided by the labrum and the tendons of the rotator cuff. The rotator cuff is comprised of four small but very powerful muscles. They wrap around the humeral head to keep it located in the glenoid. The rotator cuff also internally and externally rotates the upper arm (humerus). Above the rotator cuff tendons is a water-filled sac or bursa that reduces friction and cushions the rotator cuff tendons as they slide under the cowl of bone on top of the shoulder, the acromion.
The shoulder works in a balancing act, a force couple, between the deltoid and the rotator cuff. As you raise your arm the deltoid contracts to bring your arm up. The rotator cuff muscles contract in synchrony to depress the humeral head ointo the glenoid. If your rotator cuff muscles are weak or your deltoid overpowers them, then the shoulder subluxes (partially dislocates) and rides up against the acromion. This in turn pinches the tendons and bursa between the two. This is called impingement. Repeated often enough and the tendons and bursa become irritated and swell. This leads to tendonitis, bursitis or even a small tear in the rotator cuff tendons.
Part II will discuss factors which predispose you to rotator cuff pathology, ways to reduce the likelihood of injury, and treatment options.