Teres Minor

Introduction

Introduction to Teres Minor

The teres minor is a narrow, elongated muscle situated in the posterior scapular region of the upper limb. It is one of the four muscles that comprise the rotator cuff (along with the supraspinatus, infraspinatus, and subscapularis), which are essential for stabilizing the glenohumeral (shoulder) joint and facilitating dynamic movements of the arm.

Study

Origin and Insertion

The teres minor originates from the upper two-thirds of the lateral (axillary) border of the dorsal surface of the scapula. Its muscle fibers run superolaterally to insert onto the lowest (inferior) of the three facets on the greater tubercle of the humerus, as well as into the capsule of the shoulder joint.

Innervation and Blood Supply

Unlike the supraspinatus and infraspinatus which are supplied by the suprascapular nerve, the teres minor is innervated by the posterior branch of the axillary nerve (nerve roots C5, C6). A notable anatomical feature is that the nerve branch to the teres minor often possesses a pseudoganglion (an enlargement lacking nerve cell bodies). Its arterial supply is derived primarily from the circumflex scapular artery and the posterior circumflex humeral artery.

Actions and Biomechanics

The primary action of the teres minor, working synergistically with the infraspinatus, is the lateral (external) rotation of the arm at the glenohumeral joint. It also acts as a weak adductor of the arm. Crucially, as a rotator cuff muscle, it helps depress and stabilize the head of the humerus within the glenoid cavity during abduction, preventing superior translation of the humeral head by the deltoid.

Topographical Anatomy

The teres minor plays a vital role in forming the boundaries of anatomical spaces in the posterior shoulder. Its inferior border forms the superior boundary of both the quadrangular space (which transmits the axillary nerve and posterior circumflex humeral artery) and the triangular space (which transmits the circumflex scapular vessels).

Clinical Correlates

Isolated tears of the teres minor are rare; they are usually seen in massive rotator cuff tears. Atrophy or weakness of the muscle is most commonly secondary to a lesion of the axillary nerve (e.g., from an anterior shoulder dislocation or surgical neck fracture of the humerus). The 'Hornblower's sign' (patte test) can be used to clinically evaluate for teres minor weakness or tears.

Summary

Teres Minor Summary

Origin: Upper 2/3 of the lateral border of the scapula (posterior surface). Insertion: Inferior facet of the greater tubercle of the humerus. Innervation: Axillary nerve (C5, C6). Arterial Supply: Circumflex scapular and posterior circumflex humeral arteries. Action: Lateral rotation of the arm; stabilizes the humeral head.