| Risk Factors Shoulder instability is a condition in which the
upper-end of the humerus (the upper arm bone) slides partially
or completely out of the shoulder socket. Normally, the head of
the humerus, moves within the confines of the shoulder socket.
Instability occurs when the head slips outside its normal
position. The humeral head may move in one or more directions.
The disorder is classified by how much this bone moves and by
the direction it moves: - Subluxation—The humeral head moves
part way out of the shoulder socket. - Dislocation—The humeral
head moves completely out of the socket. - Anterior—The humeral
head moves toward the front. This is the most common form. It
typically occurs in young men. Athletes with great shoulder
flexibility are more prone to the disorder. Reinjury is more
common in teens and young adults, because they have more
elasticity in their shoulder capsule and ligaments. This can
lead to later chronic instability. Posterior—The humeral head
moves toward the back. This is often