This condition occurs when the head of the upper arm bone, the humerus, slips out of the socket formed by the scapula at the shoulder joint. Because the shoulder is not as stable as other joints, this injury is common.
This injury occurs most commonly after a fall or a sports-related injury. In a majority of these cases the humerus sits in front of the shoulder blade after dislocation. In rare cases, dislocation may occur from a violent jolt such as electrocution or a seizure, and the humerus becomes lodged behind the shoulder blade. Rarely, the humerus can become lodged beneath the glenoid.
Pain in the shoulder is the primary symptom of this condition. Other symptoms may include weakness or lack of mobility in the arm, bruising, swelling, numbness, or the arm appearing to hang low on the shoulder, often with the forearm turned outward or inward (depending on the direction of the dislocation).
The most common treatment is through a process called closed reduction. During this procedure, the head of the humerus is placed back into the shoulder socket without surgery. In severe dislocations where ligaments, tendons or nerves may have been damaged, surgery may be required.