Shoulder Instability

What is shoulder instability?
Shoulder instability is the term given to a variety of conditions when the humeral head, or ball, does not remain centered in the glenoid, or socket. The most dramatic example of this is when an individual dislocates his/her shoulder. However, the majority of individuals have a subtle instability or subluxation of the shoulder that causes them to seek medical attention. Microinstability, or brief periods where the ball is not centered in the socket, can disrupt athletic performance every bit as much as an individual who continues to redislocate the shoulder.

What causes shoulder instability?
Shoulder instability can be due to a number of causes. The most common are traumatic events (fall from a height; direct blow), abnormal tissue quality, and repetitive overuse. Traumatic events are the most obvious reason for instability. We all have seen or know of someone who fell onto their shoulder or had it violently jerked the wrong way, and had to go to the emergency room for someone to pop it back in place. Typically, the humeral head will dislocate out the front of the shoulder. Because the shoulder only comes out anteriorly, this is known as unidirectional instability. Many individuals have ligaments that are more elastic than they should, and provide an inadequate amount of support without any major injury. Since all ligaments are affected, the shoulder can dislocate or sublux in multiple directions. This is known as multidirectional instability. The difference between these conditions is critical because it dictates the prognosis and treatment of the dislocating/subluxating shoulder.