Dislocated shoulder: The shoulder joint is the most mobile joint in the body and allows the arm to move in many directions. This ability to move makes the joint inherently unstable and also makes the shoulder the most often dislocated joint in the body. Dislocations of the shoulder occur when the head of the humerus (upper arm bone) is dislocated from its socket in the shoulder blade. Ninety percent or more of shoulder dislocations are anterior dislocations, meaning that the humeral head has been moved to a position in front of the joint.
