Reviewed by Dr. Jon Warner
The shoulder is the junction of three bones: the humerus (upper arm bone), the clavicle (collarbone), and the scapula (shoulder blade). The ball-like head of the humerus fits into the cup-like end of the scapula (known as the "glenoid" or "shoulder socket"). The head of the humerus may be forced out of the glenoid in a dislocation or can be forced partially out of the glenoid, which is known as a subluxation. Either may cause a Hill-Sachs Defect, a compression fracture in the top of the humerus, caused by the head of the humerus impacting the glenoid when the dislocation occurs. To envision this, imagine a sharp edge impacting a ping-pong ball. The defect can increase the risk of further dislocations by making it easier for the humerus to slide out of the socket.
Causes and Risk Factors