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Biceps pulley

The biceps pulley is a complex fibro-ligamentous structure located within the rotator interval of the shoulder, responsible for stabilizing the long head of the biceps tendon (LHBT) within the bicipital groove. It acts as a sling, maintaining the correct alignment of the LHBT as it exits the joint capsule and passes into the intertubercular sulcus.

This pulley system is formed by an intricate interconnection of tendinous and ligamentous structures, including the superior glenohumeral ligament (SGHL), coracohumeral ligament (CHL), and fibers from the subscapularis and supraspinatus tendons. Together, they create a functional “reflection pulley” that ensures smooth gliding and prevents anterior or medial dislocation of the biceps tendon during shoulder motion.

Disruption of the biceps pulley is a common source of anterior shoulder pain and is frequently associated with rotator cuff tears, biceps tendon instability, and SLAP (superior labrum anterior-posterior) lesions.

Synonyms

  • Reflection pulley of the biceps

  • Biceps sling

  • Rotator interval pulley system

Structure and Components

  • Superior glenohumeral ligament (SGHL): Forms the medial sling supporting the LHBT at its intra-articular portion.

  • Coracohumeral ligament (CHL): Runs obliquely, blending with the supraspinatus and subscapularis tendons to form the roof of the pulley.

  • Subscapularis tendon fibers: Contribute to the medial wall of the pulley.

  • Supraspinatus tendon fibers: Form the superior wall of the pulley complex.

  • Biceps tendon reflection: The tendon curves at nearly a 90° angle from its glenoid origin into the bicipital groove, held in place by the pulley.

Location and Relations

  • Superiorly: Coracohumeral ligament and rotator interval capsule

  • Inferiorly: Lesser tuberosity and upper portion of the subscapularis tendon

  • Medially: SGHL and subscapularis tendon fibers

  • Laterally: Supraspinatus tendon and bicipital groove

  • Posteriorly: Joint capsule of the glenohumeral joint

Function

  • Stabilization: Prevents medial and anterior dislocation of the long head of the biceps tendon.

  • Guidance: Ensures smooth transition of the tendon from intra-articular to extra-articular course.

  • Load distribution: Reduces shear stress on the biceps anchor during shoulder rotation and abduction.

  • Joint synergy: Works in coordination with the rotator cuff and capsule to maintain humeral head stability.

Clinical Significance

  • Pulley lesions: May involve partial or complete tearing of the SGHL, CHL, or adjacent cuff tendons, leading to biceps instability.

  • Biceps subluxation or dislocation: Occurs when the pulley fails, causing the tendon to slip medially over the lesser tuberosity.

  • Associated pathologies: Commonly coexist with subscapularis tendon tears and superior labral injuries.

  • Pain and dysfunction: Present as anterior shoulder pain, snapping, or weakness during internal rotation.

  • Surgical relevance: Repair of the pulley system may be required during biceps tenodesis or subscapularis reconstruction.

MRI Appearance

T1-weighted images:

  • Pulley structures: Low signal intensity (dark linear bands) between the subscapularis and supraspinatus tendons.

  • Biceps tendon: Low-signal cylindrical structure seated in the bicipital groove.

  • Surrounding fat: Bright, providing contrast against the dark tendon and pulley fibers.

  • Disruption: Appears as irregular, discontinuous low-signal fibers with altered tendon contour.

T2-weighted images:

  • Normal pulley: Dark, well-defined band stabilizing the low-signal biceps tendon.

  • Partial tear: Focal hyperintense signal within the SGHL or CHL fibers.

  • Complete tear: Bright signal gap with medial displacement or subluxation of the biceps tendon.

  • Associated edema: Bright hyperintensity around the bicipital groove or rotator interval region.

STIR:

  • Normal pulley: Intermediate-to-dark signal intensity with distinct fiber continuity.

  • Pathology: Hyperintense edema or fluid around the pulley complex and biceps tendon sheath, often extending into the rotator interval.

Proton Density Fat-Saturated (PD FS):

  • Normal: Pulley fibers appear dark, continuous bands; biceps tendon dark and centrally located.

  • Tear or inflammation: Bright hyperintense signal along the SGHL or CHL, or fluid outlining the tendon in the groove.

  • Excellent for detecting subtle pulley disruption and biceps instability.

T1 Fat-Sat Post-Contrast:

  • Normal: Minimal enhancement of adjacent capsule and tendon sheath.

  • Inflamed or torn pulley: Focal or diffuse enhancement around the biceps origin and rotator interval.

  • Postoperative or chronic scarring: Shows irregular, mild enhancement without active edema.

CT Appearance

Non-Contrast CT:

  • The pulley itself is not directly visualized due to its soft-tissue nature.

  • Bicipital groove morphology and bony landmarks can be assessed.

  • Secondary signs of pathology include flattening, shallowing, or osteophyte formation along the bicipital groove.

  • Chronic instability may show cortical remodeling or sclerosis at the lesser tuberosity.

Post-Contrast CT (standard):

  • Contrast-enhanced CT highlights peritendinous inflammatory changes and fluid collections within the bicipital groove.

MRI image

Biceps pulley ligments axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000

MRI image

Biceps pulley ligments axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00001

MRI image

Biceps pulley ligments coronal cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000

MRI image

Biceps pulley ligments sagl cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000