A SLAP tear, which stands for Superior Labrum Anterior to Posterior, is a specific injury deep within the shoulder joint. This injury affects the labrum, the ring of specialized cartilage that surrounds the shoulder socket. It is a common source of shoulder pain and instability, particularly in athletes who engage in overhead activities.
The Specific Anatomy of the Shoulder Joint
The shoulder is a highly mobile ball-and-socket joint where the head of the humerus, or upper arm bone, fits into a shallow socket on the shoulder blade called the glenoid. Because the glenoid socket is naturally small and shallow, it relies heavily on surrounding structures for stability. The labrum is a circumferential rim of tough, fibrous tissue that attaches to the edge of the glenoid.
This rim of fibrocartilage acts like a rubber gasket, deepening the socket to create a more stable fit for the humerus. A SLAP tear occurs specifically in the superior (upper) aspect of this cartilaginous rim. This superior location is vulnerable because it serves as the attachment site for the main tendon of the biceps muscle.
Damage to this structure compromises the joint’s function, leading to a loss of the deepening effect it provides and impacting shoulder stability. Understanding the labrum’s role in stabilizing the shoulder joint is crucial to comprehending the impact of a SLAP injury.
Understanding the SLAP Tear Definition
The acronym S.L.A.P. precisely defines the injury’s location and direction of tearing within the shoulder joint. The “S” stands for Superior, specifying the location at the topmost part of the labrum. This is the area where the tear begins and is particularly prone to injury.
The “L” and “A” refer to the Labrum, the fibrocartilage ring, and the tear’s direction, which extends from Anterior (front) to Posterior (back). This means the tear runs along the superior rim, spanning from the front edge to the back edge of the attachment. The location is further defined by the attachment of the long head of the biceps tendon, which anchors directly into the superior labrum.
The biceps tendon’s attachment makes the labrum susceptible to injury when tension is placed on the biceps muscle. When the arm is forcefully pulled, the tendon can pull the labrum away from the bone. This mechanism explains why the biceps tendon is often involved, as the force transmits directly to the superior labrum complex.
Common Activities That Cause SLAP Tears
SLAP tears are typically caused by two main mechanisms: acute traumatic events or chronic repetitive stress. Acute trauma often involves a compression force, such as falling onto an outstretched hand or directly onto the shoulder. This sudden impact forces the head of the humerus into the glenoid socket, crushing the labrum.
Another type of acute injury is a traction force, which occurs with a sudden, forceful pull on the arm, such as trying to catch a heavy object. This pulling motion yanks on the biceps tendon, tearing the labrum from the bone. Shoulder dislocations can also cause an acute SLAP tear due to the extreme forces involved.
Repetitive stress injuries result from repeated microtrauma over time, often seen in specific occupational or athletic activities. Athletes in overhead sports like baseball, tennis, and volleyball are at high risk due to the constant, forceful motion of throwing or serving. These repeated movements cause fraying and wear on the superior labrum, eventually leading to a tear.
Identifying the Symptoms of a Labral Tear
Individuals with a SLAP tear commonly experience deep, aching pain inside the shoulder joint that can be difficult to pinpoint. This discomfort often worsens with overhead activity or reaching across the body. The pain may also be felt during seemingly simple actions, such as lifting or carrying objects.
A distinct set of mechanical symptoms is frequently reported, including a sensation of popping, clicking, or grinding within the shoulder during movement. Patients may also describe the shoulder “catching” or locking when moving the arm in certain positions. This is often due to the torn piece of labrum interfering with the normal movement of the joint.
The involvement of the biceps tendon can lead to additional symptoms, such as pain near the front of the shoulder or weakness in the arm. Throwing athletes may specifically report a decrease in throwing velocity or a sensation known as a “dead arm” after a forceful throw. If these symptoms are present, it suggests a structural injury that warrants a medical evaluation.