Corpus: Glenoid labrum

The glenoid labrum is an articular lip that forms a 3 to 4 mm wide, bulbous rim around the glenoid cavity (cavitas glenoidalis) of the scapula.

2.1. Overview

The glenoid labrum consists mostly of circumferentially oriented collagen fibers, with small amounts of fibrocartilage. It is firmly attached in the posteroinferior segment and mobile in the superoanterior segment, connected to the glenoid cavity. In the cranial part of the glenoid cavity, the labrum, together with the long head of the biceps tendon, forms the biceps tendon anchor (labrum-biceps tendon complex).

The labrum exhibits a highly variable shape and size. It is typically about 3 mm thick and 4 mm wide. In cross-section, it is usually triangular or, less commonly, round. The labrum is connected to the rotator interval, superiorly to the long head of the biceps tendon, anteriorly to the superior glenohumeral ligament, and partially to the middle glenohumeral ligament, and inferiorly to the inferior glenohumeral ligament.

2.2. Arterial supply

Arterial supply is provided by an ascending branch from the axillary artery ("ascending glenoid artery"), branches of the suprascapular artery and circumflex scapular artery, as well as muscle branches of the rotator cuff and the anterior and posterior circumflex humeral arteries. Blood supply is supplemented by the underlying bony glenoid.

2.3. Clinical anatomy

Radiologically, the labrum is described in the parasagittal plane analogously to a clock face:

• 11 to 1 o'clock: superior
• 1 to 3 o'clock: anterosuperior
• 3 to 5 o'clock: anteroinferior
• 5 to 7 o'clock: inferior
• 7 to 9 o'clock: posteroinferior
• 9 to 11 o'clock: posterosuperior

These descriptions always refer to the right shoulder. For example, the 3 o'clock position always corresponds to the anterior labrum.

The glenoid labrum enlarges the articular surface and improves the positioning of the humeral head in the glenoid cavity of the shoulder. It stabilizes the shoulder joint, opposes movements anteriorly and posteriorly, and prevents dislocation.

Variability in the labrum is greatest in the anterosuperior segment. The sublabral foramen is a common normal variant, occurring in approximately 10% of cases. Absence of the anterosuperior labrum combined with a robust middle glenohumeral ligament occurs in approximately 1 to 2 % of cases and is termed the Buford complex.

In the superior labrum, the sublabral recess is an important normal variant. It represents the most common form of the biceps tendon anchor, occurring in 70 % of cases, and should therefore be considered more the rule than the exception.

In approximately one-fifth of cases, a narrow gap may be found at the base of the posterior labrum. Typically, the posteroinferior quadrant is affected by this normal variant.

Anterior shoulder dislocation often results in a tear of the anteroinferior glenoid labrum, termed a Bankart lesion. Variants include:

• GLAD lesion
• Perthes lesion
• ALPSA lesion

Superior labral anterior-posterior (SLAP) lesions of the superior labrum occur with strong force applied to the already tensioned long head of the biceps tendon, for example, rapid lifting of heavy weights (e.g., weightlifting) or falling onto the extended, abducted arm (e.g., bicycle accidents).

Posterior labral lesions can occur with a posterior shoulder dislocation. They are distinguished between:

• Posterior Bankart lesion
• POLPSA lesion
• Kim lesion