What causes an unstable shoulder?

Shoulder instability is most commonly caused by two different problems, placing people into two different categories in terms of treatment options. The category of "post-traumatic" shoulder instability includes people with a previous injury that has stretched or torn the ligaments of the shoulder. A second category is used for people who naturally have loose shoulder joints.

A bad injury to the shoulder can cause the shoulder to become unstable by stretching or tearing the ligaments of the shoulder away from the bone. When the ligaments of the shoulder are pulled away from the bone, this type of an injury is called a "Bankhart lesion."

Shoulder instability can also be caused by a generalized looseness of the joints, which is thought to represent some type of congenital ligamentous laxity. This means that certain people are born with ligaments that are more loose than normal. These people are frequently very flexible and are often called "double-jointed," especially when they are school-age children. These people often have a shoulder that can slip out of joint in more than one direction, a condition that is called "multi-directional instability."

The younger a patient is at the time first subluxation or dislocation episode, the more likely he or she is to suffer from further episodes of instability. Conversely, shoulder instability is less of a problem as people grow older, because most people naturally become a little bit stiffer with age.

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