Shoulder Dislocations

When we speak of an unstable "shoulder" we usually are referring to the joint between the head of the humerus and the glenoid (theball and socket of the shoulder, respectively). Thus, we should more properly speak of glenohumeral instability (It is also possible to have instability at the other joints of the shoulder as well, such as the acromioclavicular, sternoclavicular, and scapulothoraic joints).

Glenohumeral instability is defined as the inability to maintain the humeral head centered in the glenoid. This condition has been recognized for many years as is revealed by a brief history.

Glenohumeral instability may arise from an injury to the bone, rotator cuff, labrum, capsule, and/or the ligaments which normally prevent excessive rotation. This we call "traumatic" instability. The most commonly torn ligaments run across the lower front part of the joint and prevent excessive rotation when the arm is held out to the side and rotated backward (as in a baseball throw). It takes a major force to tear these ligaments, such as a high energy fall with a landing on the arm (as in skiing). Recurrent traumatic instability typically produces symptoms when the arm is placed in positions near that of the original injury. If the ligaments do not heal after the first injury (which is often a complete dislocation), the arm continues to be unstable when it is held out to the side and rotated backward. In these circumstances, a surgical repair of these ligaments is usually successful in restoring stability to the shoulder. The post operative exercises are essential to optimizing the result of surgery.

A shoulder can become unstable without a major injury if it loses the ability to balance the muscle forces around it. The joint starts to slip when the arm is used out in front or down at the side. We call this "atraumatic" instability. Once the balance is lost, dedication to a regular muscle balancing exercise program is required to get it back. If the stabilizing mechanisms become severely decompensated, surgery to tighten the tissues around the joint can be of temporary benefit; but, it the final analysis, muscle balance must be restored through exercises if stability is to be regained. The postoperative rehabilitation after this surgery is particularly important.

There are a few instances where shoulder instability cannot be classified into one of these two groups. In these uncommon situations, we speak of Intermediate types of recurrent instability.