The shoulder joint is like a ball and a cup. The ball (humeral head) is held in the cup (glenoid) by both the shape of the bones, and the ligaments and capsule surrounding the joint. With a shoulder dislocation, the ball comes out of the socket. For this to occur, the ligaments and capsule stabilizing the shoulder must tear or stretch. The labrum is a thin rim of tissue surrounding the edge of the shoulder socket. When the labrum tears, this is called a ‘Bankart lesion’.
Most shoulder dislocations are due to a traumatic injury, such as a fall. Occasionally an individual may develop a ‘loose’ or unstable shoulder with repetitive microtrauma (baseball pitchers, swimmers), or even without trauma.
A dislocation is obvious; the arm is held at the side, and cannot be voluntarily moved without severe pain. A loose, or unstable shoulder that is not dislocated may cause feelings of not being able to ‘trust’ the shoulder. This is especially true when the arm is overhead and out to the side. There may be a sense of ‘catching’ in the shoulder, followed by vague aching.
A positive ‘apprehension’ test, or being able to recreate the feeling that the shoulder is about to ‘come out of the socket’.
The diagnosis is primarily based on history and physical examination. X-rays are occasionally helpful. An MR scan may show a tear in the labrum.
Prolonged immobilization after a dislocation probably doesn’t reduce the risk of redislocation. Aggressive physical therapy, working on strengthening the muscles around the shoulder, can reduce symptoms, but may not prevent recurrence.
The ligaments holding the ball in the socket are repaired(if torn), or tightened (if loose). This may be done either arthroscopically with a fiberoptic camera, or with an open procedure.
Recurrent dislocation is the main complication with this type of injury. The risks of recurrence and chronic instability are much greater in the younger individual, and decrease with age.