The labrum is a cartilage ring that surrounds the shoulder socket (called the glenoid) and makes it deeper. In the above picture, it is numbered "5" - the thin blue ring around the glenoid. Since the socket is deepened by the labrum, the ball of the arm bone (called the head of the humerus) has a better fit into it. Labrum or labral tears are usually associated with trauma, instability of the shoulder, or repetitive throwing as with a baseball player.

The signs and symptoms of a labral tear are painful clicking, locking, or popping. Instability may be present because the labrum is not doing its job of holding the ball in the socket. Medical intervention for a labral tear typically involves an MRI for diagnosis and arthroscopic repair but labral tears are often hard to diagnose. A special kind of labral tear, a superior labral anterior to posterior (SLAP) tear, often involves the biceps tendon as well.