Instability of the shoulder is a more common problem than in any other single joint. This occurs because the shoulder joint, while a ball-in-socket joint, has a very shallow socket. Someone described the shoulder joint as a basketball on a cymbal or a golf ball on a tee. This allows a tremendous range of motion of nearly a hemisphere. The penalty for this motion is instability. Compare the range of motion of the shoulder to the hip, which is also a ball-in-socket joint. However, the hip has a much deeper socket and sacrifices motion for stability.

Instability of the shoulder occurs in multiple situations. The most common cause is a fall on an outstretched hand or an injury such as a tackle in football. 98% or more of shoulder dislocations will be anteriorly (the ball comes out of the socket and moves anteriorly). In this situation the arm will usually be held slightly abducted and externally rotated. Reduction can usually be accomplished with pain medicine and sedation.

A posterior dislocation is much less common and occurs in approximately 2-4% of cases. This usually occurs with a fall with the arm at the side and an posteriorly directed force. This is most common in auto accidents. This dislocation is commonly missed and difficult to diagnose. The classic position is to have the arm at the side and internally rotated. The treatment is closed reduction.

A third kind of instability in multi-directional. In this instability the ball can go anteriorly, posteriorly or inferiorly or any combination of the three. This type of instability rarely responds to non-surgical treatment. The patient choices are to live with the instability or progress to surgery.

There are different types of instability. The pure traumatic type is the typical one. There is also a voluntary dislocation. This occurs when the individual can “pop” the shoulder out at will. This is often done as a means of entertainment. The final classification is an involuntary dislocation. This is usually an individual who voluntarily dislocated the shoulder so many times that he has totally lost control of the stability and it will dislocate despite his best efforts to maintain that stability.

Prognosis

Some of the older authors from the 60’s and 70’s advocated three weeks of immobilization before starting a mobilization period. They felt that this significantly decreased the chances of repeat dislocation.

However, more recent studies have suggested that the risk of repeat dislocation is primarily age dependent and immobilization is of secondary importance. The chance of dislocation depends upon the age at the time of the first dislocation. If the individual was less than 20 years old, the chance of repeat dislocation is approximately 50% and may be higher. Between ages 20-30 the chances of repeat dislocation is 30-40%. The chance of repeat dislocation if the first dislocation occurs over age 30 is 10% or less. Similarly, different studies have argued about the values of post dislocation physical therapy. My personal philosophy after a first time dislocation is to immobilize for three weeks and then begin an aggressive physical therapy program. I feel that this is the best chance of achieving a stable shoulder long term. While there are certainly arguments that this is not necessary I think that a three week period of immobilization is a “cheap insurance policy” if we can possibly prevent repeat dislocations.

If the shoulder dislocates a second time surgery may be recommended. After a third dislocation there is no option and surgery will be necessary to prevent redislocations. There is some evidence to suggest that repetitive dislocations can lead to premature arthritis.

TREATMENT

There are well over 100 procedures that have been described for the treatment of shoulder instability. However, they fall into three basic categories. 1) Muscle transfer techniques. These are rarely used anymore except as an adjunct to other procedures. 2) The Bankart procedure consists of reattaching the ligaments that extend between the ball and the socket. 3) The Bristow procedure involves taking the small piece of bone with the attached biceps tendon muscle to the front of the socket. This effectively blocks redislocation. The results of the Bankart and Bristow procedure have been approximately the same in the literature. The chance of dislocation after one of these procedures is in the 1-2% range. There is a small risk of injury to the nerves and the standard risk of infection common to any surgical procedure. Shoulder surgery has no unusual incidence of infection.

Recently, there has been the development of arthroscopic techniques. These essentially do a Bankart type procedure. This can be achieved through the small arthroscopy incisions. The arthroscopic procedures have the primary advantage of avoiding the restriction of motion that commonly occurs in standard open surgery. However, they also have slightly higher rate of redislocation. Therefore, I usually recommend arthroscopic procedures for those individuals that absolutely require a throwing motion. This might include high school pitchers and quarterbacks. I would recommend a standard open procedure for a high school football lineman. A young girl with relatively low demands may also be better off with the cosmetically more aesthetic arthroscopic technique if she is willing to accept the higher rate of repeat dislocation.