Glenoid Labrum: Anatomy, Function, Clinical Role, MRI & CT Arthrogram

Topic

Glenoid labrum

The glenoid labrum is a fibrocartilaginous rim attached to the margin of the glenoid cavity of the scapula. It deepens the glenoid fossa, enhancing shoulder joint stability by increasing the articular surface area and serving as an attachment for the joint capsule and glenohumeral ligaments.

The labrum blends with the tendon of the long head of the biceps brachii superiorly and the joint capsule inferiorly. It is triangular in cross-section, with its base fixed to the glenoid rim and the free edge projecting inward toward the humeral head. The labrum’s structure allows flexibility and shock absorption while maintaining stability during shoulder motion.

Synonyms

Glenoidal labrum
Glenoid fibrocartilaginous rim
Glenoid lip

Location and Structure

Location: Around the entire margin of the glenoid cavity of the scapula.
Shape: Triangular cross-section, thickest inferiorly, thinner superiorly.
Composition: Dense fibrocartilage containing collagen fibers interwoven with the joint capsule.
Attachments:
- Superiorly: Blends with the tendon of the long head of the biceps brachii.
- Inferiorly: Continuous with the inferior glenohumeral ligament complex.
- Anteriorly: Attached to the glenoid margin, often involved in Bankart-type lesions.
- Posteriorly: Firmly adherent to the glenoid rim, may show normal recess (posterior sublabral foramen).

Relations

Superiorly: Biceps tendon and supraglenoid tubercle.
Inferiorly: Glenohumeral ligaments and inferior capsule.
Anteriorly: Subscapularis tendon and middle glenohumeral ligament.
Posteriorly: Infraspinatus and teres minor tendons.
Medially: Glenoid rim of scapula.
Laterally: Articular surface of humeral head.

Nerve Supply

Articular branches from the suprascapular nerve and axillary nerve.

Function

Deepens glenoid cavity: Increases surface area and depth for the humeral head, enhancing stability.
Shock absorption: Distributes forces transmitted through the glenohumeral joint.
Capsular attachment: Serves as anchoring structure for the joint capsule and ligaments.
Biceps integration: Superior portion transmits tension from the biceps long head tendon.
Joint stability: Prevents anterior and posterior humeral head translation during movement.

Clinical Significance

Labral tears: Common cause of shoulder pain and instability; include Bankart (anterior-inferior) and SLAP (superior) lesions.
Degeneration: Seen in overhead athletes and with aging.
Detachment or avulsion: From trauma or dislocation; may lead to recurrent instability.
Variants: Sublabral recess or foramen may mimic tear on imaging.
Imaging importance: MRI and MR arthrography are gold standards for assessing labral tears and variants; CT arthrography is valuable when MRI is contraindicated.

MRI Appearance

T1-weighted images:
- Labrum: Low signal (dark), triangular structure at glenoid rim.
- Marrow of glenoid: Bright due to fatty signal.
- Tears: Appear as linear or wedge-shaped high/intermediate signal clefts between labrum and glenoid rim.
- Joint capsule: Low-signal line continuous with labral base.
T2-weighted images:
- Labrum: Low signal (dark)
- Tear or detachment: Bright hyperintense fluid signal extending into or under the labrum.
- SLAP lesion: Linear hyperintensity extending into superior labrum and biceps anchor.
- Bankart lesion: Disruption of anteroinferior labrum with adjacent cortical irregularity or fracture.
STIR:
- Normal labrum: Low signal (dark)
- Pathology: Bright hyperintense signal along labral base indicating edema or tear.
- Highlights associated capsular or periarticular soft-tissue changes.
Proton Density Fat-Saturated (PD FS):
- Normal labrum: Dark, well-defined triangular margin.
- Tear: Focal or linear bright signal extending to articular surface or glenoid rim.
- Excellent for differentiating true tears from sublabral recesses.
T1 Fat-Sat Post-Contrast:
- Normal labrum: Minimal enhancement.
- Tear or inflammation: Focal contrast enhancement or outlining of tear cleft.
- Post-surgical scar: Enhancing tissue around the labrum; recurrent tears remain non-enhancing.

MRI Arthrogram Appearance

Direct MR arthrography: Intra-articular contrast outlines labral margins.
Tears: Appear as contrast-filled clefts or separation between labrum and glenoid rim.
Bankart lesions: Contrast tracks between anteroinferior labrum and bone; may extend to periosteum.
SLAP lesions: Contrast extends between superior labrum and biceps anchor.
Sublabral recess: Smooth, well-defined contrast entry posterior to biceps tendon (normal variant).
Best for differentiating true detachment from anatomic variants.

CT Appearance

Non-Contrast CT:

Labrum: Not directly visualized (soft-tissue density similar to cartilage).
Glenoid rim: Clearly defined cortical bone.
Indirect signs: Bony Bankart fragment, cortical irregularity, or labral calcification.

Post-Contrast CT (standard):

Soft-tissue contrast enhancement allows limited labral visualization.
May show pericapsular inflammation or hematoma in acute injury.

CT Arthrogram Appearance

Labrum: Outlined by intra-articular iodinated contrast.
Tears: Contrast extends under or into the labrum forming a linear cleft.
Bankart lesion: Contrast fills defect at anteroinferior glenoid margin, often with bone fragment.
SLAP lesion: Contrast extends between superior labrum and glenoid rim at biceps origin.
Advantages: High spatial resolution for bony and post-traumatic labral injuries, particularly useful if MRI is contraindicated or postoperative.