Teres minor muscle

At a glance

English

Teres minor muscle

Latin (TA2)

Musculus teres minor

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the teres minor muscle

Teres minor is a narrow, elongated muscle at the back of the shoulder and the smallest of the rotator cuff group. It lies just below infraspinatus, with which it is often partly fused, and above teres major. Like the other cuff muscles, its tendon merges with the shoulder joint capsule and helps keep the head of the humerus seated in the shallow glenoid cavity.

Its fibres arise from the upper two-thirds of the back of the lateral border of the scapula and from fibrous sheets that separate it from its neighbours. They run up and out, behind the long head of triceps, and finish on the lowest of the three facets of the greater tubercle; the lowest fibres attach to the bone just below that facet. The tendon blends with the back of the joint capsule on the way.

The muscle rotates the arm laterally, working with infraspinatus and the back part of deltoid, and adds a little adduction. Its stabilising role matters most when the arm is lifted: it pulls the humeral head down and back, countering the upward pull of deltoid so the head does not ride up against the acromion.

Teres minor is supplied by the posterior branch of the axillary nerve, which shows a small swelling of nerve fibres as it enters, sometimes called a pseudoganglion. The muscle forms the upper border of the quadrangular space, through which the axillary nerve and posterior circumflex humeral artery run. Compression in that space, from fibrous bands, cysts or widened veins, can cause shoulder pain, tingling down the arm and wasting confined to teres minor, which shows on ultrasound or MRI. In most tears of the cuff, by contrast, this muscle stays intact.

Attachments, action and supply

Origin

Upper two-thirds of the dorsal surface of the lateral border of the scapula and adjacent fibrous septa.

Insertion

Lowest facet on the humerus's greater tubercle, plus the back of the shoulder joint capsule.

Action

Laterally rotates the arm and weakly adducts it; with the rest of the cuff, keeps the humeral head centred in its socket.

Nerve supply

Axillary nerve, posterior branch (C5, C6).

Blood supply

Circumflex scapular artery and posterior circumflex humeral artery.