Causes of Shoulder Instability

Shoulder instability often follows an injury that causes the shoulder to dislocate.  This initial injury is usually fairly significant. It is important that the shoulder be reduced, or put back in the socket.  Sometimes individuals can achieve this on their own; however, often physician assistance is required in the Emergency Department. Two injuries occur with a dislocation that often leads to recurrent dislocations. 1. The labrum is often torn away from the bone. 2. The ligaments in the capsule are stretched (like a rubber band that has been overstretched- it becomes loose and floppy.)  An unstable shoulder can result in repeated episodes of dislocation, even during normal activities.


In some cases, shoulder instability can happen without previous dislocation.  People who do repeated shoulder motions may gradually stretch out the joint capsule.  This is especially common in athletes such as baseball pitchers, swimmers and volleyball players.  If the joint capsule gets stretched out and the shoulder muscles weaken the ball of the humerus begins to slip around too much within the shoulder.  Eventually this can cause irritation and pain in the shoulder.

A genetic problem with connective tissues of the body can lead to ligaments that are too elastic.  When ligaments stretch too easily, they may not be able to hold joints in place.  All the joints in the body may be too loose.  Some joints, such as the shoulder, may be easily dislocated.  People with this type of condition are sometimes referred to as double jointed.

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