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Subscapularis tendon

The subscapularis tendon is the strong, broad tendon of the subscapularis muscle, the largest and most powerful component of the rotator cuff. It arises from the subscapular fossa on the anterior surface of the scapula and inserts onto the lesser tubercle of the humerus.

The tendon crosses the anterior aspect of the shoulder joint, reinforcing its capsule and providing dynamic stability. Acting primarily as an internal rotator of the humerus, it also prevents anterior displacement of the humeral head. The tendon’s upper fibers interdigitate with the capsule and the coracohumeral ligament, while its inferior portion is tendinous and muscular.

Synonyms

  • Tendon of subscapularis muscle

  • Lesser tubercle tendon

  • Anterior rotator cuff tendon

Origin, Course, and Insertion

  • Origin (muscle): Entire costal surface of the subscapular fossa of the scapula, separated by ridges for tendinous septa.

  • Course: Fibers converge laterally and superiorly, passing anterior to the shoulder joint capsule.

  • Insertion:

    • Main attachment: Lesser tubercle of the humerus and its crest.

    • Capsular fibers: Blend with the anterior capsule of the shoulder joint.

    • Superior portion: Interdigitates with fibers of the supraspinatus tendon near the rotator interval.

Relations

  • Anteriorly: Subscapular bursa, coracoid process, coracobrachialis, and short head of biceps brachii.

  • Posteriorly: Shoulder joint capsule and humeral head.

  • Superiorly: Coracohumeral ligament and supraspinatus tendon.

  • Inferiorly: Anterior humeral circumflex artery (deep plane), axillary recess.

  • Medially: Subscapular fossa and serratus anterior.

  • Laterally: Lesser tubercle and bicipital groove (intertubercular sulcus).

Nerve Supply

  • Upper and lower subscapular nerves (C5–C7), branches of the posterior cord of the brachial plexus.

Function

  • Medial (internal) rotation of the humerus.

  • Dynamic stabilization of the shoulder joint — resists anterior translation of the humeral head.

  • Assists in adduction and depression of the humeral head during arm elevation.

  • Forms anterior component of the rotator cuff, working with supraspinatus, infraspinatus, and teres minor.

Clinical Significance

  • Subscapularis tendon tears: Often occur at the superior portion or humeral insertion; may be isolated or part of massive rotator cuff tears.

  • Biceps instability: The tendon helps stabilize the long head of the biceps tendon; tears often cause biceps dislocation.

  • Subcoracoid impingement: Compression between the coracoid and lesser tubercle may injure the tendon.

  • Degeneration and calcific tendinopathy: Common with age and overuse.

  • Post-surgical importance: Tendon repair integrity is crucial after rotator cuff surgery; re-tears affect shoulder mechanics.

MRI Appearance

  • T1-weighted images:

    • Tendon: Low signal (dark), clearly defined fibers inserting on lesser tubercle.

    • Muscle belly: Intermediate signal with distinct fascicular pattern.

    • Marrow of lesser tubercle: Bright fatty signal.

    • Tear: Discontinuity or gap with intermediate-to-bright signal; retraction of muscle belly if chronic.

    • Biceps tendon displacement: Seen adjacent to subscapularis tear (medial biceps subluxation).

  • T2-weighted images:

    • Normal tendon: Low signal intensity.

    • Muscle: Intermediate-to-dark, slightly darker than T1.

    • Partial tear or tendinosis: Linear or focal bright signal within tendon.

    • Full-thickness tear: Fluid-bright hyperintense gap with tendon retraction.

    • Peritendinous fluid: Hyperintense signal in subcoracoid space or anterior recess.

  • STIR:

    • Normal tendon and muscle: Intermediate-to-dark signal.

    • Pathology: Bright hyperintensity in edema, strain, or acute tear.

    • Sensitive for detecting inflammation and muscle atrophy.

  • Proton Density Fat-Saturated (PD FS):

    • Normal tendon: Dark, continuous low signal.

    • Partial tears/tendinopathy: Focal bright hyperintense zones within tendon substance.

    • Full-thickness tears: Bright signal extending from articular to bursal surface.

    • Muscle edema: Hyperintense signal, best visualized on coronal or axial views.

  • T1 Fat-Sat Post-Contrast:

    • Normal tendon: Minimal enhancement.

    • Tendinitis: Enhancing peritendinous tissue or synovium.

    • Tear with granulation: Peripheral enhancement with central low-signal fluid.

    • Postoperative tendon repair: Heterogeneous enhancement may indicate healing or residual inflammation.

CT Appearance

Non-Contrast CT:

  • Tendon: Soft-tissue density anterior to humeral head, not easily separated from capsule.

  • Insertion site: Lesser tubercle well defined; cortical irregularity or erosions indicate enthesopathy.

  • Calcific tendinitis: Seen as dense focal calcification within tendon or near insertion.

  • Muscle: Homogeneous soft-tissue density in subscapular fossa.

  • Chronic tear: May show fatty atrophy and muscle retraction.

Post-Contrast CT (standard):

  • Tendon: Slight enhancement if inflamed.

  • Peritendinous soft tissue: Enhancing areas indicate bursitis, synovitis, or postoperative inflammation.

  • Utility: Defines bony changes, calcific deposits, and chronic cortical erosion better than MRI.

MRI image

Subscapularis tendon axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Subscapularis tendon axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI image

Subscapularis tendonsagl cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Subscapularis tendon ct axial