The Teres minor is a small, narrow muscle of the rotator cuff group in the shoulder. It is important for the stabilization and rotation of the shoulder joint. As part of the rotator cuff, it works with other muscles to provide stability and support to the glenohumeral (shoulder) joint, playing a crucial role in the shoulder’s mobility and stability mechanisms.
Location
The Teres minor is located in the upper portion of the lateral side of the scapula, just inferior to the infraspinatus muscle. It originates from the lateral border of the scapula and inserts into the lower facet of the greater tubercle of the humerus. It lies above the teres major muscle and is one of the smaller muscles that contribute to the rotator cuff.
Anatomy
Origin
The Teres minor originates from the upper two-thirds of the lateral border of the scapula. This origin point is just below the scapular spine and adjacent to the origin of the infraspinatus muscle, another rotator cuff muscle.
Insertion
The muscle fibers travel laterally and slightly upward to insert into the lower facet of the greater tubercle of the humerus. This insertion point is located just below the insertion of the infraspinatus muscle on the humerus, contributing to the integrated function of the rotator cuff muscles.
Structure
The Teres minor is a rounded and somewhat flattened muscle when viewed in anatomical position. It is smaller and more narrow compared to the adjacent infraspinatus muscle. The muscle fibers run obliquely from the scapula to the humerus, forming a tendonous band as they approach the humerus.
Relations
- Superficially: The Teres minor is covered by the deltoid muscle, which must be moved aside in anatomical dissections to view the Teres minor.
- Deeply: It lies superior to the Teres major muscle and inferior to the infraspinatus muscle, with the latter being part of the rotator cuff as well.
- Medially: It is bordered by the long head of the triceps brachii muscle.
Blood Supply
The arterial supply to the Teres minor comes primarily from the circumflex scapular artery, a branch of the subscapular artery. This ensures the muscle receives sufficient oxygen and nutrients for its functions.
Innervation
The Teres minor is innervated by the axillary nerve (C5, C6), which arises from the posterior cord of the brachial plexus. This nerve also supplies sensation to the skin over part of the deltoid area (regimental badge area) and innervates the deltoid muscle.
Function
The Teres minor muscle has several important functions in the shoulder joint as part of the rotator cuff:
- External (Lateral) Rotation of the Arm: The primary function of the Teres minor is to assist in rotating the arm laterally (outward). This action is crucial for various activities such as reaching up or throwing.
- Stabilization of the Shoulder Joint: Along with the other rotator cuff muscles, the Teres minor helps stabilize the head of the humerus in the glenoid cavity of the scapula. This stabilization is vital during arm movements to prevent dislocation and ensure smooth motion.
- Contributes to Arm Adduction: Although not its primary role, the Teres minor helps in the adduction of the arm (movement of the arm towards the body).
By performing these functions, the Teres minor contributes significantly to the range of motion and stability of the shoulder, enabling a wide variety of arm movements.
Clinical Significance
The Teres minor muscle holds significant clinical relevance, particularly in the context of shoulder health and dysfunction:
Rotator Cuff Injuries: The Teres minor is one of the four muscles that constitute the rotator cuff, a critical muscle group for shoulder stability and motion. Injury to the rotator cuff, including tears or strains of the Teres minor, can lead to pain, weakness, and reduced range of motion in the shoulder. Identifying and treating Teres minor injuries is essential for the rehabilitation of rotator cuff disorders.
Shoulder Impingement Syndrome: This condition occurs when there is excessive pressure on the muscles of the rotator cuff from the surrounding bone structures. Given the Teres minor’s role and location, it can be involved in impingement syndromes, leading to pain and functional limitations.
Postural Issues: Poor posture, particularly forward rounding of the shoulders, can strain the Teres minor and other rotator cuff muscles, leading to discomfort and potential injury. Addressing Teres minor function is often part of therapy for correcting shoulder posture.
Surgical Considerations: In surgeries involving the shoulder, such as those addressing rotator cuff injuries, the condition and functionality of the Teres minor are critical considerations. Its integrity is crucial for successful surgical outcomes and the restoration of shoulder function.
Physical Therapy and Rehabilitation: The Teres minor is a focus in many rehabilitation programs for shoulder injuries. Strengthening and stretching exercises targeting this muscle and the rest of the rotator cuff are fundamental for recovering shoulder stability and function after injury or surgery.
