Posterior labral tears are injuries to a specific type of cartilage found only in the body's socket joints: the shoulders and the hips. A labral shoulder tear is more common than a similar tear of the hip, owing to the greater use of the upper extremities in general and the greater range of motion usually demanded of the joint in everyday use. The labrum itself is a special type of cartilage surrounding a socket, designed to cushion the joint and to increase the depth of the shoulder's glenoid socket that the ball of the humerus — or upper arm bone — lies within, thereby increasing overall joint stability. Posterior labral tears occur in the posterior, or rear, aspect of the labrum. They are usually classified as either a superior labrum anterior to posterior (SLAP) tear or a posterior labral tear with impingement.
SLAP tears are one of the types of posterior labral tears, and involve the upper aspect of the labrum from front to back. These tears are classified into four categories depending upon the degree of injury, the specific aspects of the shoulder anatomy involved and the degree of interventional repair anticipated. One of the four categories of SLAP tears is further subdivided into three types, depending upon the area or areas of injury, beginning at the front of the shoulder and progressing to the rear. Posterior labral tears classified as SLAP tears also involve the anterior, or top, aspect of the labrum and thus the area where the head of the biceps muscle connects to the shoulder. They most often affect individuals who must repeatedly use an overhead arm motion, such as baseball pitchers or wood choppers who use an ax.
Posterior labral tears may also often occur with impingement, or pinching, of the shoulder's rotator cuff. This impingement occurs less often than SLAP tears but is also seen in athletes, particularly football players. Posterior labral tears with impingement affect the stability of the shoulder because of the rotator cuff's involvement. The rotator cuff is actually comprised of four separate muscles that work together to provide both stability and flexibility to the shoulder joint. Full dislocation of the humerus from the shoulder is rare with rotator cuff injury, but sublaxation — instability felt with movement — is a common complaint.
Despite their specific classification, posterior labral tears share some similar symptoms. Shoulder pain is usually described as deep or aching and located in the joint area itself. Other symptoms include reports of a subjective instability or a specific pull or catch when repeating a typical shoulder motion. Diagnosis usually requires an MRI or CT scan, although smaller tears might require an arthroscopic evaluation to confirm.