Pathoanatomy: (The Problem)
There are various forms of shoulder instability. The shoulder is an amazing joint which allows for a very large range of motion–much more than any other joint in the body. The price of this extensive motion is a somewhat tenuous relationship between flexibility and stability. The ligaments and muscles responsible for shoulder stability must be finely tuned to walk the fine line between stability and mobility. Sometimes as a result of trauma the ligaments are disrupted, allowing abnormal movement of the humeral head on the glenoid (the two components of the shoulder joint). Thereafter, when the shoulder is in a certain position it can dislocate.

Shoulder instability, however, can occur even without trauma. Some patients have greater than average laxity of their ligaments due to genetic factors, and this can sometimes result in a more chronic shoulder instability. In this case, there is not a specific tear or disruption of the shoulder ligaments, but all of them are somewhat loose, resulting in abnormal shoulder motion.

Symptoms and Signs: (What it feels like)
It is hard to mistake a traumatic shoulder dislocation. They are usually quite dramatic and require an emergency room visit for reduction. Thereafter, recurrences of the dislocation may not be quite as dramatic or severe, but are still quite painful and harmful to the shoulder joint. The pain usually occurs toward the front of the joint. There is often apprehension on the part of the patient about putting their shoulder into certain positions. Often various sports or activities are given up because of the inability to trust the shoulder in these situations. X-ray appearance often reveals a fracture in the back of the humerus where it has impaled itself on the glenoid during dislocation.

Nontraumatic instability is much more subtle. Frequently the patient has relatively lax ligaments throughout the body and can hyperextend various joints. There may not be dramatic dislocations but just chronic pain from instability. X-rays may be normal and at first, symptoms may be hard to distinguish from other shoulder problems.

Natural History: (What happens with no treatment)
There is a distinct difference between traumatic instability in the young and the older patient. The recurrence rate in patients under 30 is very high, approaching 80% or 90%, whereas in the over 40 patient, it is relatively rare to have a recurrence. The treatment is therefore different in these two groups, tending toward surgical repair in the young and conservative treatment in a sling for the older patients. If the shoulder is allowed to continue to dislocate, whatever the age of the patient, increasing damage to the joint will result, leading to posttraumatic arthritis.

In the nontraumatic dislocator or unstable shoulder, the natural history is variable. Some patients will have their symptoms resolve spontaneously over the years, perhaps because of a change in their activities or possibly as a result of the aging process. Others require extensive strengthening and rarely, surgery, to resolve their instability.

Treatment and Options:
For the young patient with failure of conservative care, surgery provides the best option for stabilizing the recurrently dislocating shoulder. There are various techniques for this procedure, some of which can be accomplished arthroscopically; however, there is a slightly higher recurrence rate with this procedure as opposed to the open surgical technique.

In the older patient with traumatic instability, it is almost always best to treat in a sling for a few weeks, as this will often result in a stable shoulder. Occasionally, associated fractures or rotator cuff tears will require surgical repair.

The treatment options for the nontraumatic unstable shoulder always start with physical therapy and strengthening. Surgical intervention in this situation is not as predictable and is a last resort only. New techniques for thermally shrinking or tightening loose ligaments offer some promise for this and other types of shoulder instability.

Surgical Intervention:
The arthroscopic technique for stabilization requires the repair of the torn ligamentous tissue and is an outpatient procedure. The scars are relatively small, and the rehabilitation involves 3 to 4 weeks in a sling and then progressive range of motion and strengthening exercises. The open procedure is performed through an anterior incision and again involves the suture repair of the torn ligaments. The postoperative routine involves first sling immobilization and then progressive motion and strengthening activities. The risks include infection, bleeding, nerve or blood vessel damage, and failure of the procedure to prevent recurrence. The long-term outcome is usually quite good, with many patients regaining what feels to them to be a nearly normal shoulder.