ACC Sports Sciences Feature: Shoulder Instability
Jan. 5, 2005
Scott C. Montgomery, M.D.
The shoulder is an inherently unstable joint. If a hip joint is a ball in a cup, then the shoulder joint is a ball on a golf tee; it can easily fall off. This allows both the large functional range of motion needed to perform a free-style stroke and the potential to slip off the tee. Instability can result in a dislocation if the shoulder is knocked all of the way out of the joint or a subluxation if it moves part of the way out of the joint. There are two main types of shoulder instability -- traumatic and atraumatic. Traumatic instability involves an initial event in which the shoulder pops out of place (dislocation), usually requiring someone else to put it back in place. While traumatic instability is more common in contact athletes such as football and lacrosse, atraumatic instability is common in sports that emphasize repetitive activities, such as swimming, and more often results in subluxation. As the name suggests, this type of instability does not result from a single injury to the shoulder but rather a stressful activity repeated many times resulting, over time, in micro-trauma to the shoulder which causes the symptoms and ultimate reduction in peak athletic performance.
Who gets shoulder instability?
Physical exam findings help diagnose instability. Many swimmers have generalized hyperlaxity (double jointed). This in itself does not predict shoulder pain, but implies atraumatic instability. In fact, it might be a big reason why a swimmer can perform at an elite level in the first place. The most common criteria physicians use for judging lax joints in the body looks at bending the thumb to the forearm, elbow hyperextension, and the shoulder sulcus. Laxity only becomes a problem when it causes pain and does not allow the athlete to continue to function at a high level.
Specific exam findings can aid the diagnosis. An apprehension test is performed with the patient on her back, with her arm abducted and externally rotated. The patient feels pain and an uncomfortable feeling that their shoulder might slide out of its socket. This apprehensive feeling is often relieved with pressure on the front of the humerus with the arm in the same position. This relocates the shoulder in its socket and relieves the uncomfortable feeling and quite often the pain.
Non-operative therapy (rehab)
The "gold standard" procedure for an athlete with symptomatic posterior instability is the posterior capsular shift. Recently, advances in arthroscopic surgery have allowed physicians to treat symptomatic shoulder instability entirely through the scope. Both anterior and posterior capsular laxities, which are often causes of the atraumatic instability, can be addressed with an arthroscopic capsular shift using plication sutures. In traumatic instability, the Bankhart lesion can be seen and repaired directly to the edge of the socket. Various suture anchor systems and suture passers allow accurate reattachment of the capsule. Current arthroscopic methods achieve results that compare favorably with open methods while preserving motion and resulting in much less operative pain. Whether open or through a scope, the whole point of surgery is to tighten up and repair the structures around the shoulder to help better keep it balanced on the golf tee.
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