Shoulder instability occurs when the upper-end of the arm bone, known as the humerus, slides partially or completely out of the shoulder socket.

The disorder is classified by how much the humerus moves and the direction of the movement:

  • 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.
  • Posterior—The humeral head moves toward the back.
  • Multidirectional

Shoulder Instability
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Shoulder instability often results from injury.