The glenoid labrum is the rubber-like gasket that goes around the rim of the shoulder socket. It deepens the socket and helps with stability of the shoulder. The long head of the biceps attaches to the top of the socket into the labrum.
The labrum can occasionally be injured or torn, usually associated with a dislocation or subluxation of the shoulder. It can also be injured thru repetitive trauma, such as throwing, where the pull on the biceps can strip the labrum off the bone. In some cases, labral tears can lead to recurrent instability, such as in shoulder dislocation. In other cases, pieces or flaps of the torn labrum can become entrapped in the joint, causing pain.