The teres minor is a small, elongated muscle on the lateral scapular border directly inferior to the infraspinatus, sharing external rotation function but with different innervation from the axillary nerve rather than the suprascapular nerve. Together with the infraspinatus it forms the posterior rotator cuff external rotators, and it is the structure directly posterior to the quadrilateral space through which the axillary nerve and posterior circumflex humeral artery pass.
| Origin | Upper two-thirds of the lateral border of the scapula |
|---|---|
| Insertion | Inferior facet of the greater tuberosity of the humerus |
| Nerve Supply | Axillary nerve (C5, C6) — posterior branch |
| Blood Supply | Posterior circumflex humeral artery |
| Actions | External rotation of the arm; Inferior stabilisation and compression of the glenohumeral joint |
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Although anatomically separate from the infraspinatus and with different nerve supply, the teres minor is functionally inseparable from it in clinical assessment and rehabilitation. Its smaller size makes its individual contribution to external rotation difficult to isolate clinically.
The quadrilateral space syndrome involves compression of the axillary nerve and posterior circumflex humeral artery between the teres minor superiorly, teres major inferiorly, long head of triceps medially, and surgical neck of the humerus laterally. MRI shows isolated teres minor denervation oedema and fatty infiltration in this condition, which is the key to distinguishing it from other causes of posterior shoulder pain. Isolated teres minor tears are uncommon but can occur in massive posterosuperior rotator cuff tears.
The teres minor is palpable between the infraspinatus above and the teres major below along the lateral scapular border, becoming firm during resisted external rotation with the arm abducted to 90 degrees.
Axillary nerve and artery compression in the quadrilateral space producing posterior shoulder pain and teres minor denervation on MRI in overhead athletes, managed with activity modification and decompression surgery.
