The shoulder has the most range of motion of any of the major joints in the body. Maintaining stability in this highly mobile and versatile joint requires a finely tuned combination of many structures in the athlete. The socket (glenoid), the cartilaginous rim around the socket (labrum), the capsular ligaments, and the rotator cuff muscles all play a role in stability.
A frequent cause of pain or instability of the throwing shoulder is a labral tear. A particular kind of labral tear involving the superior labrum is a SLAP (Superior Labrum Anterior to Posterior) tear. This tear originates where the long head of the biceps tendon attaches to the labrum and glenoid.
SLAP tears can be traumatic, from overuse, or degenerative. Repetitive forces such as those seen with overhead and/or throwing athletes are frequently responsible for SLAP lesions. Other common mechanisms of injury include blows to the shoulder, a fall on an outstretched arm, seatbelt/shoulder harness injuries, or heavy lifting. People with a SLAP tear often feel a deep-seated pain often referred to the back of the shoulder. But depending on the extent of biceps involvement can be felt anteriorly as well. Sudden movements or extremes of motion, especially outwards and upwards as in throwing, often bring on the pain. Occasionally, catching sensations or instability symptoms are also felt.