Original Article: http://www.mayoclinic.com/health/medical/IM02999
A dislocation is an injury to your joint in which the ends of your bones are forced from their normal positions. Your shoulder, which is a ball-and-socket joint, is a common site for dislocation. The ball is your upper arm bone (humerus), and the socket is part of your shoulder blade (scapula). In a shoulder dislocation, these two bones are forced from their normal positions.