Rotator Cuff Muscles
The four rotator cuff muscles form a continuous musculotendinous cuff that compresses the humeral head against the glenoid fossa, providing dynamic stability to a joint that prioritises range of motion over bony constraint.
✦ The Mnemonic
"Shoulder Integrity Through Stability"
SITS — four muscles that dynamically stabilise the glenohumeral joint
Clinical Breakdown
The rotator cuff muscles arise from the scapula and insert onto the greater (supraspinatus, infraspinatus, teres minor) and lesser (subscapularis) tuberosities of the humerus. Their tendons blend with the capsule to form a continuous cuff. The supraspinatus is most vulnerable because it passes under the coracoacromial arch, where repeated impingement leads to degeneration and tearing.
Painful arc test: pain between 60–120° of passive abduction suggests supraspinatus impingement or a partial tear. Full-thickness supraspinatus tears cause weakness and inability to initiate abduction — though the deltoid can maintain abduction beyond 15° once initiated passively. Night pain, particularly when lying on the affected shoulder, is characteristic.
Testing individual muscles: Supraspinatus — Jobe's (empty can) test at 90°/30° of abduction in internal rotation. Infraspinatus/Teres minor — external rotation lag sign. Subscapularis — lift-off test (internal rotation against resistance behind the back) and belly-press test.
⭐ Clinical Pearl
Axillary nerve injury (C5, C6) from anterior shoulder dislocation or proximal humeral fracture causes loss of deltoid and teres minor, with a sensory patch over the 'regimental badge' area of the lateral shoulder. The axillary nerve is at risk during inferior approaches to the glenohumeral joint — the safe zone is >5 cm distal to the lateral acromion.