The subscapularis is divided functionally into upper (tendinous) and lower (musculotendinous) portions, with the lower fibres arising from the lower subscapular fossa and inserting into the lesser tubercle and anterior capsule. The lower portion is innervated by the lower subscapular nerve and contributes disproportionately to internal rotation power rather than the joint stabilisation role of the upper tendinous portion.
| Origin | Inferior two-thirds of the subscapular fossa, from the lower oblique ridges |
|---|---|
| Insertion | Lesser tubercle of the humerus (lower fibres) and anterior glenohumeral capsule |
| Nerve Supply | Lower subscapular nerve (C5, C6) |
| Blood Supply | Subscapular artery |
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It medially rotates the arm and helps stabilise the humeral head against forward displacement, especially with the arm at the side.
Subscapularis tears are increasingly recognised, comprising up to 30% of all rotator cuff tears. Partial tears most commonly affect the superior third (upper tendinous portion), while complete tears progress inferiorly. The belly-press test, lift-off test, and bear-hug test assess lower and upper subscapularis integrity separately. MRI evaluates the musculotendinous junction and the degree of fatty infiltration of the lower muscle belly, which predicts repair outcome.
The lower subscapularis is not directly palpable. Tenderness at the lesser tubercle with the arm in slight extension and external rotation suggests subscapularis pathology.
Tear of the lower musculotendinous junction from forceful external rotation, producing positive belly-press and bear-hug tests with relative preservation of the lift-off test if the upper tendon remains intact.
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