Subscapularis Anatomy

Origin

• Medial two-thirds of the subscapular fossa (anterior surface) of the scapula.
• Some fibers arise from tendinous intramuscular septa attached to ridges on the bone.

Insertion

• The fibers converge into a broad tendon that passes anterior to the joint capsule.
• Site: Lesser Tuberosity of the Humerus.
• Extension: The tendon extends inferiorly to the surgical neck.
• Fibrous Expansion: Some fibers extend over the bicipital groove to the Greater Tuberosity (forming the Transverse Humeral Ligament roof).

Nerve Supply

Unlike other cuff muscles, it has dual innervation from the Posterior Cord:

1. Upper Subscapular Nerve (C5, C6)

• Enters the muscle superiorly/medially.
• Supplies the upper fibers.

2. Lower Subscapular Nerve (C5, C6)

• Enters the muscle inferiorly.
• Supplies the lower fibers.
• Continues to supply the Teres Major.

This redundancy means total paralysis is rare unless the posterior cord is injured.

Key Relations

• Anterior: Serratus Anterior (gliding plane - scapulothoracic joint), Coracobrachialis, Short Head Biceps (Conjoined Tendon).
• Posterior: Glenohumeral Joint Capsule (Anterior band). The tendon is intimately adherent to the capsule, reinforcing it (Glenohumeral Ligaments).
• Inferior: Axillary Nerve and Posterior Circumflex Humeral Artery (Quadrangular Space).
• Lateral: Biceps Tendon (Long Head) in the groove. Subscapularis forms the medial wall of the bicipital sheath (pulley).

Key Surface Landmarks

• Coracoid Process: The 'Lighthouse' of the shoulder. Palpable 2cm inferior to the clavicle in the deltopectoral groove.
• Lesser Tuberosity: Palpable lateral to the coracoid when the arm is externally rotated.
• Deltopectoral Groove: The location of the cephalic vein and the interval for the open approach.

Palpation

• Axillary Approach: In abduction, the lower border of the subscapularis can be palpated in the axilla (anterior fold).
• Tendon: Difficult to palpate directly as it is deep to the coracoid and conjoined tendon.

External rotation brings the lesser tuberosity out from under the coracoid, facilitating palpation.

Lafosse Classification (Arthroscopic)

Based on the extent of the tear from Superior to Inferior (Rolled edge).

• Type I: Partial lesion of superior one-third (Leading edge).
• Type II: Complete lesion of superior one-third.
• Type III: Complete lesion of superior two-thirds.
• Type IV: Complete lesion of entire tendon (Head centered).
• Type V: Complete lesion with Anterosuperior Escape (Head migrates up and forward).

Implication: Type I/II can be repaired via standard portals. Type III/IV often require accessory portals or open approach. Type V needs reverse arthroplasty or complex reconstruction.

This classification guides the approach (Arthroscopic vs Open) and the rehabilitation protocol.

Fox & Romeo Classification

• Type I: Partial thickness tear.
• Type II: Complete tear of upper 25%.
• Type III: Complete tear of upper 50%.
• Type IV: Complete rupture of entire tendon.

This classification correlates with the likelihood of finding the 'Comma Sign' in Type III and IV tears.

MRI

• Axial View: Best for assessing the tendon insertion and retraction.
• Sagittal Oblique: "Comma Sign" evaluation.
• Findings:
  • Tendon discontinuity.
  • Fat infiltration (Goutallier stage) in the muscle belly (Scapular Y view).
  • Biceps subluxation (medial) indicates a Subscapularis tear (pulley loss).
  • Subcoracoid Stenosis: Reduced coracohumeral distance (less than 6mm) predicts impingement.

CT Scan

• CT Arthrogram: Historical gold standard. Useful if MRI is contraindicated or for bony avulsion (Lesser Tuberosity).

Ultrasound

• Dynamic assessment.
• Can visualize the "Rolling" of the tendon under the coracoid (check for impingement).
• Accuracy: Lower than for Supraspinatus, often because the insertion is deep to the coracoid.

Ideally, dynamic ultrasound should be performed by a musculoskeletal radiologist to ensure accuracy.

Diagnostic Scope

• Position: 30-degree scope from posterior portal.
• Manoeuvre: "Lever push" or "Internal Rotation" of the arm is required to see the insertion footprint. In neutral, only the upper portion is visible.
• Comma Sign: A comma-shaped arc of tissue at the superolateral border, formed by the disrupted SGHL/CHL complex attached to the torn subscapularis edge. Marker for the torn edge.

The "Comma Sign" is the single most important landmark for finding a retracted tear.

Management Algorithm

• Urgency: Subscapularis tears retract and undergo fatty atrophy FASTER than Supraspinatus tears. Early repair is advocated.

Young patients with acute tears should be prioritized for surgery within 2 weeks to optimize outcomes.

Deltopectoral Approach

• Incision: Coracoid to deltoid insertion.
• Interval: Pectoralis Major (Medial) and Deltoid (Lateral). Cephalic vein preserved (usually laterally).
• Exposure: Clavipectoral fascia incised. Conjoined tendon retracted medially.
• "The Three Sisters": Anterior Circumflex Humeral vessels (leash) mark the inferior border of the Subscapularis. must be ligated.

Tendon Management (Arthroplasty)

• Peel: Subperiosteal release (for repair).
• Tenotomy: Division 1cm from insertion (easy to close).
• Osteotomy: Lesser tuberosity osteotomy (Bone-to-bone healing, rare now).

The osteotomy has a high union rate but rehabilitation is slower due to bone healing precautions.

Arthroscopic Repair

• Portals: Posterior (View), Anterior (Work), Anterosuperior (Access).
• Steps:
  • Biceps: Tenotomy or tenodesis is usually required.
  • Coracoplasty: Resection of the lateral coracoid tip if impingement is present.
  • Release: 3-sided release (Anterior, Posterior, Superior). Note: Beware Axillary Nerve inferiorly!
  • Mobilization: Traction sutures are key.
  • Fixation: Suture anchors in lesser tuberosity.

Double-row repair is biomechanically superior but technically more demanding in the tight subscapular space.