Teres minor is the inferior component of the posterior rotator cuff, below infraspinatus, inserting on the inferior greater tuberosity facet. It is the only rotator cuff muscle supplied by the axillary nerve (all others are supplied by the suprascapular nerve). It participates in the posterior rotator cuff force couple balancing the anterior (subscapularis) force.
| Origin | Lateral border of the scapula (superior two-thirds of the dorsal surface) |
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| Insertion | Inferior facet of the greater tuberosity of the humerus; teres minor occupies the lowest facet of the three tuberosity facets (below infraspinatus) |
| Nerve Supply | Posterior branch of the axillary nerve (C5-C6); the branch enters the muscle inferiorly — this is why the posterior branch is vulnerable in quadrilateral space syndrome |
| Blood Supply | Posterior circumflex humeral artery; circumflex scapular artery |
| Actions | External rotation of the shoulder (primary function); assists in adduction; inferior stabilizer of the humeral head; contributes to posterior cuff force couple with infraspinatus |
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Isolated teres minor atrophy on MRI is pathognomonic of axillary nerve injury at the quadrilateral space, producing the classic pattern of deltoid weakness with preserved external rotation and teres minor wasting. This distinguishes quadrilateral space syndrome from suprascapular nerve palsy at the spinoglenoid notch (infraspinatus only) or at the suprascapular notch (both supra and infraspinatus). Teres minor fat infiltration is graded in rotator cuff tear staging as it correlates with posterior cuff function.
MRI demonstrating isolated teres minor fatty atrophy without infraspinatus involvement is pathognomonic of axillary nerve injury at the quadrilateral space; deltoid atrophy accompanies teres minor wasting, and the normal infraspinatus confirms the lesion is distal to the suprascapular nerve take-off, localising the injury to the posterior axillary nerve branch.
