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Subscapular fossa

The subscapular fossa is the concave anterior (costal) surface of the scapula that lies adjacent to the posterior thoracic wall. It serves as the origin site of the subscapularis muscle, one of the four rotator cuff muscles. The fossa forms a shallow depression that conforms to the curvature of the ribs and acts as a gliding surface between the scapula and thoracic cage, separated by the subscapularis fascia and serratus anterior muscle.

The fossa plays a key biomechanical role in shoulder stabilization and internal rotation, transmitting muscular force from the subscapularis to the humerus via the rotator cuff mechanism.

Synonyms

  • Costal surface of the scapula

  • Anterior surface of the scapula

  • Subscapular depression

Location and Structure

  • Position: Anterior (costal) surface of the scapular body.

  • Shape: Broad, shallow, triangular concavity facing the thoracic cage.

  • Surface features:

    • Smooth, with ridges and lines for the attachment of subscapularis muscle fibers.

    • Covered by subscapularis fascia, which thickens laterally to form the subscapular bursa between the muscle and the neck of the scapula.

  • Boundaries:

    • Superior border: Corresponds to the superior angle and suprascapular notch.

    • Inferior border: Near the inferior angle of scapula.

    • Medial border: Adjacent to the vertebral margin and serratus anterior.

    • Lateral border: Leads to the glenoid fossa and neck of scapula.

Relations

  • Anteriorly: Serratus anterior and thoracic wall (ribs and intercostal muscles).

  • Posteriorly: Subscapularis muscle attached along its surface.

  • Medially: Vertebral border of the scapula, related to rhomboid muscles.

  • Laterally: Neck of scapula and glenohumeral joint capsule.

  • Superiorly: Suprascapular vessels and nerve near the superior angle.

Attachments

  • Subscapularis muscle: Originates from the entire subscapular fossa and its ridges.

  • Subscapular fascia: Lines the fossa, providing a smooth gliding surface for muscle movement.

  • Subscapular bursa: Lies between the muscle and neck of scapula, reducing friction during motion.

Nerve Supply

  • Upper and lower subscapular nerves (C5–C7) from the posterior cord of the brachial plexus supply the subscapularis muscle overlying the fossa.

Function

  • Muscular origin: Provides attachment for the subscapularis, facilitating shoulder internal rotation.

  • Shoulder stability: Integral component of the rotator cuff mechanism, stabilizing the humeral head in the glenoid cavity.

  • Gliding interface: Smooth curvature permits movement of the scapula over the thoracic cage during respiration and shoulder motion.

  • Force transmission: Conveys muscular forces from subscapularis to humerus, aiding upper limb control.

Clinical Significance

  • Fractures: Rarely isolated; may occur with scapular body or glenoid fractures.

  • Bursitis: Inflammation of the subscapular bursa may cause anterior shoulder pain.

  • Muscle pathology: Subscapularis tendinopathy or tears can alter the contour and fat signal of the fossa on MRI.

  • Winged scapula: Loss of smooth scapulothoracic gliding due to serratus anterior paralysis.

  • Neoplasm or infection: Tumors or abscesses may occupy the fossa, displacing the subscapularis muscle.

  • Imaging importance: MRI and CT define bone, muscle, and bursal pathology in trauma or chronic shoulder conditions.

MRI Appearance

  • T1-weighted images:

    • Bone cortex: Low signal (dark).

    • Marrow: Bright due to fatty composition.

    • Subscapularis muscle: Intermediate signal.

    • Fascia and periosteum: Low signal outlining the fossa.

    • Pathology: Fractures or sclerosis appear as low-signal lines; soft-tissue masses or muscle atrophy show intermediate-to-bright changes.

  • T2-weighted images:

    • Bone cortex: Dark.

    • Marrow: Bright, slightly less than fat on T1.

    • Subscapularis muscle: Intermediate-to-low, darker than T1.

    • Bursa or effusion: Hyperintense signal adjacent to lateral fossa.

    • Pathology: Edema, hemorrhage, or tumor infiltration appear bright hyperintense.

  • STIR:

    • Normal bone marrow: Intermediate-to-dark signal.

    • Abnormal marrow or muscle edema: Bright hyperintense signal.

    • Excellent for identifying stress fractures, bursitis, or inflammation.

  • Proton Density Fat-Saturated (PD FS):

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

    • Pathology: Focal bright hyperintensity in marrow or muscle from edema or tendinopathy.

    • Useful for detecting subtle subscapular bursitis or early muscular strain.

  • T1 Fat-Sat Post-Contrast:

    • Normal marrow: Homogeneous mild enhancement.

    • Inflammation or bursitis: Focal enhancement along subscapular recess or bursa.

    • Tumor or infection: Irregular or nodular enhancement patterns.

CT Appearance

Non-Contrast CT:

  • Bone cortex: High attenuation and sharply marginated.

  • Subscapular fossa: Seen as a shallow concavity on the costal surface of the scapula.

  • Marrow: Homogeneous trabecular pattern.

  • Pathology: Excellent visualization of fractures, bone cysts, or erosive changes.

  • Bursa: Occasionally seen as a thin fat or fluid plane between subscapularis and bone.

Post-Contrast CT (standard):

  • Bone: Minimal enhancement.

  • Soft tissues: Enhancing margins in bursitis or inflammatory changes.

  • Usefulness: Defines extent of bursal effusion, fracture healing, or peri-scapular mass involvement.

CT images

subscapular fossa of scapula CT sag image -img-00000-00000

MRI images

scapular body MRI SAG IMAGE

MRI images

subscapular fossa mri image

CT VRT image

Subscapular fossa 3d vrt image

MRI image

Subscapular fossa of scapula axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000