Shoulder instability can result from a traumatic event such as a shoulder dislocation or from overuse with repetitive throwing activities. A dislocation is when the humeral head (ball portion) slips out of the shoulder socket (glenoid). The most common form of shoulder dislocation results in the humeral head dislocating out the front of the shoulder (anterior dislocation, Figure 1). Some patients may have chronic instability with repeat shoulder dislocations occurring with minor force. Patients with chronic instability usually require surgery. Arthroscopic surgical repair is often done on an outpatient basis to address this issue. Open reconstructive surgery is sometimes necessary to address socket abnormalities (such as loss of glenoid bone).
The shoulder joint has three major bony structures: the shoulder blade (scapula), the collarbone (clavicle), and the upper arm bone (humerus). The humeral head lies in the glenoid. The humeral head is larger than the glenoid (Figure 2). A soft fibrous tissue rim called the glenoid labrum surrounds the socket to help stabilize the joint in addition to other important structures (rotator cuff). The rim deepens the socket by up to 50% so that the humeral head fits better. In addition, it serves as an attachment site for several important ligaments that are crucial to maintaining shoulder stability.
Mechanisms of injury
Injuries to the tissue rim surrounding the glenoid can occur from acute trauma or repetitive shoulder motion. Examples of traumatic injury include falling on an outstretched arm, direct blow to the shoulder joint, a sudden pull, and violent overhead reach. Throwing athletes or weightlifters can experience glenoid labral tears as a result of repetitive shoulder motion.
Glenoid labral tear symptoms include pain with overhead activities, catching, locking, popping, or grinding, sense of instability of the shoulder, motion loss, and weakness.
Diagnosis of instability and labral tears is initially done with a thorough history and physical exam. Range of motion, stability, and pain with motion are all evaluated. Initial screening x-rays are obtained to evaluate for bony abnormalities. Additional imaging studies such as a computed tomography (CT) scan or magnetic resonance imaging (MRI) scan with contrast may be performed to evaluate for a labral tear. Tears can be located either above (superior) or below (inferior) the middle of the glenoid. There are different types of labral tears. A SLAP lesion (superior labrum, anterior to posterior ) is a tear of the rim above the middle of the glenoid that may also involve the biceps tendon. A tear of the rim below the middle of the glenoid that also involves the inferior gleno-humeral ligament is called a Bankart lesion.
Initial treatment may involve anti-inflammatory medication and activity reduction to relieve symptoms. Physical therapy may also be recommended. If these non-operative measures are insufficient, your physician may recommend surgical intervention.
Arthroscopic surgery involves evaluation of the glenoid rim, labrum, and the biceps tendon. Surgical repair is performed for unstable tears of the labrum with anchors and suture material. Bankart lesions are reattached to tighten the shoulder joint by folding over and reapproximating the tissues.
Most patients will wear a sling or similar device for 4 to 6 weeks. Physician directed gentle, passive, pain-free range-of-motion exercises are initially emphasized. Strengthening typically begins approximately 8 weeks after surgery. Unrestricted activity usually begins 4 to 6 months after surgery.