Glenoid labrum

At a glance

English

Glenoid labrum

Latin (TA2)

Labrum glenoideum

System

Cartilage

Region

Upper limb

Side

Paired, left and right

About the glenoid labrum

The shoulder is a ball-and-socket joint, but its bony socket is small and shallow. The glenoid cavity of the scapula is pear-shaped and covers at most about a third of the humeral head at any moment, so the joint relies heavily on soft tissue for stability. The glenoid labrum is part of that soft tissue: a fibrous rim, sometimes called the glenoid ligament, attached around the whole circumference of the cavity. It was long described as fibrocartilage, but it is now regarded as mostly dense fibrous tissue with only a thin zone of fibrocartilage where it meets bone.

In section the labrum is triangular. Its broad base is fixed to the bony margin of the glenoid and blends with the articular cartilage, and its thin, sharp free edge projects towards the humeral head. Above, it merges with the long-head tendon of biceps brachii, which arises from the supraglenoid tubercle and sends two bundles of fibres into the labrum on either side. Its front part gives attachment to the glenohumeral ligaments, and it blends with the fibrous capsule around its outer surface. The upper part is often more loosely attached than the lower.

By adding a lip around the cavity, the labrum deepens the socket by roughly half and enlarges its contact area. It works with the capsule and rotator cuff to keep the head centred, and it helps create a suction effect that resists displacement.

Tears follow acute injuries such as dislocation or a blow to the shoulder, or repeated overhead motion in throwing, swimming and similar sports. A tear of the lower front labrum after an anterior dislocation, the Bankart lesion, leaves the shoulder prone to further dislocation. A SLAP lesion, a tear of the superior labrum running from front to back, affects the upper rim where the biceps tendon joins it; it causes pain with overhead movement, catching or clicking, weakness, and pain on resisted elbow bending. Clinical tests such as O'Brien's, Speed's, Yergason's, the crank and apprehension tests load the labrum or biceps anchor to provoke pain, and contrast MRI or CT helps show the tear. Detached labrum is usually reattached to bone, often by arthroscopy.

Attachments and function

Attaches from

Its base is attached around the bony margin of the glenoid cavity of the scapula.

Attaches to

Above it merges with the long-head biceps tendon at the supraglenoid tubercle; its outer surface blends with the capsule and glenohumeral ligaments.

Function

Deepens and widens the glenoid socket, helps keep the humeral head centred and anchors the long head of biceps and the glenohumeral ligaments.

Nerve supply

Supplied, with the capsule, by branches of the suprascapular, axillary and lateral pectoral nerves.

Blood supply

Its periphery is supplied by the suprascapular, circumflex scapular and anterior and posterior circumflex humeral arteries; the inner part is poorly vascular.