The Labral Labyrinth: SLAP injuries – Part 1

Serbia’s Adriana Vilagos in action during the women’s javelin throw. Heiko Junge/NTB.

Shoulder pain and injury are common in the general and athletic populations. The glenohumeral joint is a very shallow but mobile joint that acquires most of its stability from the surrounding soft tissue structures, including the glenoid labrum. Injury to the superior glenoid labrum where the long head of the biceps tendon inserts is known as a SLAP (superior labrum anterior to posterior) injury or SLAP tear. 

SLAP injuries occur most commonly with repetitive motion from overhead sports or from traumatic injury, such as a fall on an outstretched arm, where both mechanisms represent a biomechanical mismatch between force and fixation. The presentation is usually deep shoulder pain that may present as bicep pathology.

Clinicians typically require magnetic resonance imaging (MRI) to evaluate the superior labrum and assess the condition of the biceps tendon. Management can be either non-surgical or surgical, depending on factors such as the patient’s age, activity demands, symptom severity, and the presence of shoulder instability.

Anatomy

Glenohumeral Joint
The glenohumeral joint (GHJ) is a shallow ball-and-socket joint. The ball of the humeral head fits into the glenoid fossa of the scapula. In reality, the glenoid fossa looks more like a saucer, covering only a third of the surface area of the humeral head. Due to the shallow glenoid fossa, the GHJ is reliant on other static and dynamic structures to offer stability. The static stabilizers consist of the glenohumeral ligaments, the glenoid labrum, and the capsule, while the rotator cuff and scapular muscles offer dynamic stability. What the joint lacks in stability, it makes up for with its extensive mobility⁽¹⁾. 

Labrum 
The fibrocartilaginous glenoid labrum deepens and widens the area that receives the humeral head by 75% superior-inferiorly and 50% anterior-posteriorly⁽¹⁾. It attaches directly to the glenoid and has a unified appearance. It can sometimes be meniscoid and hang over the edge, which may be mistaken for a tear on a scan. However, this is a normal anatomical variant in 1% of patients⁽²⁾. The Buford complex is found in approximately 1.5% of patients and is often benign and a normal anatomical variant. It is characterized by a bare area of the anterior superior labrum and an associated thickened middle glenohumeral ligament (MGHL)⁽³⁾. The labrum serves as both a cushion and a stabilizer for the humeral head and provides attachment points for the capsule, glenohumeral ligaments, and the long head of the biceps. Furthermore, the labrum acts like a rubber ring in a suction cup, which helps to create a negative pressure seal that holds the humeral head snugly in place. It receives its blood supply from the capsule and periosteal vessels of the glenoid, with the anterior superior labrum having the poorest blood supply⁽²⁾.

Biceps Tendon
About 50% of the long head of the biceps tendon fibers attach to the superior labrum, and the other 50% attach to the supraglenoid tubercle. Most commonly, the bicep tendon attaches to the labrum in the 12 o’clock position. It traverses the GHJ, where its blood supply is at its poorest. It then exits through the bicipital groove and continues down the arm⁽⁴⁾. It provides dynamic anterior and superior stability to the humeral head during movement, especially during overhead movements, and acts as a barrier to subluxation. This makes this area vulnerable in overhead and traction-based activities⁽²⁾.