The Teres Minor Muscle is a narrow, long muscle of the rotator cuff. It originates from the lateral border of the scapula and inserts onto the greater tubercle of the humerus. It plays a critical role in stabilizing the shoulder joint and helps center the humeral head in the glenoid cavity.

Anatomy

Morphology and Connection Points

The teres minor originates from the dorsal surface of the lateral border of the scapula. This origin generally receives support from two aponeurotic septa located between the infraspinatus and teres major muscles. The muscle inserts on the posteroinferior aspect of the greater tubercle of the humerus, i.e., the lowest trace of this process. This placement supports the stabilizing role of the teres minor, which is located posteriorly among the rotator cuff muscles. Among anatomical variations, a small additional muscle structure called the teres minimis or teres micro may be observed in some individuals. While this variation does not alter normal teres minor function, it is important to recognize during surgical or radiological evaluations. The teres minor works synergistically with the infraspinatus muscle, and together these two muscles contribute to external rotation of the shoulder. Furthermore, the muscle fibers insert into the shoulder joint capsule, directly contributing to the stabilization of the glenohumeral joint.

Embryological Origin and Classification

The teres minor is a muscle within the scapulohumeral muscle group that originates from the posterior region of the upper extremity. Embryologically derived from the dorsal mesodermal mass, this muscle, like the other rotator cuff muscles, is a specialized muscle that enables multidirectional movement and provides joint stability.

Nerve Innervation and Vascular Supply

The teres minor is innervated by the posterior branch of the axillary nerve. This nerve branch exhibits a unique configuration in the muscle's innervation, forming a structure called a pseudoganglion, which contains nerve fibers but no nerve cells. This anatomical feature may explain possible neurological variations in muscle nerve conduction. The muscle's blood supply is primarily provided by branches of the posterior circumflex humeral artery and the subscapular artery. This vascular structure supports the muscle's functional continuity by meeting its oxygen needs.

Function and Clinical Relationships

The primary function of the teres minor is to allow lateral rotation, or external rotation, of the humerus. It helps stabilize the humeral head by counteracting the upward displacement created by the deltoid, particularly during shoulder abduction. It also contributes to adduction movement along with the posterior deltoid. This muscle, part of the rotator cuff, plays a critical role in the stability of the glenohumeral joint. Clinically, the teres minor is one of the muscles that usually remains intact in rotator cuff injuries. Rotator cuff tears can be acute or chronic. Acute tears occur as a result of sudden and forceful movements (e.g., sports activities such as baseball pitching or water skiing) or traumatic falls. Chronic tears develop as a result of repetitive microtrauma or tendon friction against bone. The infraspinatus and supraspinatus tendons are the most commonly affected structures in this chronic process; the teres minor remains intact in most cases. Diagnostic evaluation utilizes magnetic resonance imaging (MRI) and ultrasonography to assess tears and tendon integrity. Conservative treatment is primarily preferred; physical therapy and, if necessary, steroid injections may be administered. However, for severe tears or cases that fail to respond to conservative treatment, surgical repair may be necessary.