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Glenohumeral joint capsule

The glenohumeral joint capsule is a fibrous envelope that encloses the shoulder joint, one of the most mobile and least stable joints in the body. It surrounds the articulation between the humeral head and glenoid cavity of the scapula, providing both flexibility for movement and structural support.

The capsule is relatively thin and loose, allowing a wide range of motion, but reinforced by ligaments, tendons, and the rotator cuff muscles. It attaches medially to the margin of the glenoid cavity (beyond the glenoid labrum) and laterally to the anatomical neck of the humerus. The inferior portion of the capsule is weakest and most distensible, forming the axillary recess (or inferior capsular pouch), which accommodates abduction and elevation of the arm.

Synonyms

  • Shoulder joint capsule

  • Capsula articularis humeri

  • Fibrous capsule of the glenohumeral joint

Location and Structure

  • Shape: Loose, fibrous sleeve surrounding the shoulder joint.

  • Extent:

    • Medially: Attaches to the periphery of the glenoid cavity beyond the labrum.

    • Laterally: Attaches to the anatomical neck of the humerus, extending farther inferiorly on the medial side.

  • Thickness: Thin and lax superiorly and inferiorly; thicker anteriorly where reinforced by ligaments.

  • Lining: Inner surface lined by synovial membrane that forms folds and recesses, including the axillary pouch and biceps tendon sheath.

Relations

  • Superiorly: Coracohumeral ligament, supraspinatus tendon, and subacromial bursa.

  • Inferiorly: Axillary recess (capsular pouch) and long head of triceps tendon.

  • Anteriorly: Subscapularis tendon, subscapular bursa, and glenohumeral ligaments.

  • Posteriorly: Infraspinatus and teres minor tendons.

  • Medially: Glenoid cavity and labrum.

  • Laterally: Neck of the humerus.

Ligamentous Reinforcements

  • Superior glenohumeral ligament (SGHL): Extends from the supraglenoid tubercle to the lesser tubercle; stabilizes the humeral head in neutral position.

  • Middle glenohumeral ligament (MGHL): From anterior glenoid margin to the lesser tubercle; limits external rotation.

  • Inferior glenohumeral ligament complex (IGHL): Thickest part, with anterior and posterior bands; supports the joint in abduction and external rotation.

  • Coracohumeral ligament: Strengthens the capsule superiorly; resists inferior displacement of humeral head.

Nerve Supply

  • Suprascapular nerve (C5–C6) – supplies superior aspect.

  • Axillary nerve (C5–C6) – supplies anterior and posterior capsule.

  • Lateral pectoral nerve – may contribute to anterior innervation.

Function

  • Joint stability: Maintains articulation between the humeral head and glenoid cavity.

  • Mobility: Allows wide range of shoulder movement — flexion, extension, abduction, adduction, and rotation.

  • Load distribution: Evenly transmits forces between humeral head and glenoid labrum.

  • Protection: Encases the synovial membrane and lubricated joint surfaces.

  • Dynamic control: Works in coordination with rotator cuff muscles and ligaments to prevent dislocation.

Clinical Significance

  • Capsulitis (Frozen shoulder/Adhesive capsulitis): Thickening and fibrosis of capsule causing stiffness and pain.

  • Capsular tear: May occur with anterior shoulder dislocation or rotator cuff injury.

  • Instability: Lax capsule predisposes to recurrent dislocations, especially in athletes.

  • Synovitis or effusion: Seen in inflammatory conditions (rheumatoid arthritis, bursitis).

  • Postoperative changes: Capsular contracture or scarring may limit range of motion.

  • Imaging relevance: MRI assesses capsular thickness, tears, recess distension, and synovial inflammation.

MRI Appearance

  • T1-weighted images:

    • Capsule: Low signal (dark fibrous band) surrounding joint margins.

    • Marrow: Bright in humeral head and glenoid due to fatty content.

    • Labrum and ligaments: Low signal structures blending with capsule.

    • Synovial fluid: Intermediate-to-bright, depending on composition.

    • Pathology: Thickened, irregular, or low-signal capsule with adjacent fat obliteration indicates fibrosis or adhesive capsulitis.

  • T2-weighted images:

    • Capsule: Low-to-intermediate signal; uniform and thin in normal state.

    • Joint fluid: Bright hyperintense outlining capsule and recesses.

    • Axillary recess: Distended with fluid in effusion or synovitis.

    • Pathology: Increased signal within capsule (inflammation), thickening (>4 mm), or focal discontinuity (tear).

  • STIR:

    • Normal capsule: Intermediate-to-dark signal.

    • Pathology: Bright hyperintensity in capsular or pericapsular regions indicating edema or inflammation.

    • Useful for detecting capsulitis, synovitis, and periarticular edema.

  • Proton Density Fat-Saturated (PD FS):

    • Normal capsule: Thin, dark low-signal band.

    • Effusion or synovitis: Bright fluid signal expanding recesses.

    • Inflamed capsule: Thickened and bright, sometimes extending into rotator interval.

    • Excellent for evaluating capsular tears, recess fluid, or fibrosis.

  • T1 Fat-Sat Post-Contrast:

    • Normal capsule: Mild peripheral enhancement.

    • Synovitis or capsulitis: Intense, diffuse enhancement of capsule and synovium.

    • Chronic fibrosis: Peripheral rim enhancement with central low-signal fibrotic tissue.

    • Useful for differentiating active inflammation from scarring.

MRI Arthrogram Appearance

  • Contrast distribution: Intra-articular gadolinium distends the joint capsule, outlining its recesses and margins.

  • Axillary recess: Normally fills uniformly; loss of distension indicates adhesive capsulitis.

  • Capsular tear: Contrast extravasation beyond capsule margins.

  • Synovial thickening: Irregular filling defects or folds.

  • Rotator interval enhancement: Common in early capsulitis.

  • Utility: Best for detecting capsular adhesions, tears, and subtle instability.

CT Appearance

Non-Contrast CT:

  • Capsule: Thin, soft-tissue density line surrounding joint; difficult to delineate without contrast.

  • Bony margins: Glenoid and humeral head cortices appear smooth and well-defined.

  • Pathology: Detects associated fractures, calcification, or chronic ossification of capsule.

  • Joint effusion: Appears as soft-tissue density in joint space, displacing capsule.

CT Arthrogram Appearance

  • Contrast injection: Iodinated contrast distends joint capsule and outlines its contour.

  • Normal capsule: Smooth, well-defined outline with uniform contrast distribution.

  • Adhesive capsulitis: Restricted distension; obliterated axillary recess.

  • Capsular tear: Contrast extravasation into surrounding soft tissues or subscapularis recess.

  • Labral or ligament involvement: Contrast leakage into subscapular recess or through capsular defects.

  • Clinical value: Best for patients contraindicated for MRI; excellent spatial resolution for assessing capsular integrity, labral relationships, and joint capacity.

 

MRI image

Glenohumeral joint capsule axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Glenohumeral joint capsule sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Glenohumeral joint capsule ct sag image