action of teres minor

3 min read 19-03-2025

The teres minor is a small, but mighty, muscle located in the posterior (back) shoulder. Often overshadowed by its larger neighbor, the infraspinatus, the teres minor plays a crucial role in shoulder stability and movement. Understanding its anatomy and action is vital for physical therapists, athletic trainers, and anyone interested in shoulder health.

Anatomy of the Teres Minor

The teres minor is one of the four rotator cuff muscles. It originates from the lateral border of the scapula (shoulder blade), specifically the upper two-thirds of the axillary border. Its fibers run laterally and slightly superiorly to insert onto the greater tubercle of the humerus (upper arm bone), just inferior to the infraspinatus insertion. This close proximity and shared insertion point often lead to them being functionally linked.

The teres minor is innervated by the axillary nerve (C5-C6), the same nerve that innervates the deltoid muscle. This shared innervation contributes to the coordinated movements between the teres minor and the deltoid.

Action of the Teres Minor: External Rotation and Shoulder Stability

The primary action of the teres minor is external rotation of the shoulder joint. This means it rotates the arm outwards away from the body. Think of twisting a doorknob clockwise. This action is particularly important during activities like throwing, swimming, or any movement requiring external rotation.

Beyond external rotation, the teres minor contributes significantly to shoulder stability. Its role in stabilizing the glenohumeral joint (the shoulder joint itself) is essential for preventing subluxation (partial dislocation) and injury. This stabilization occurs through its attachment to the humerus and its synergistic action with other rotator cuff muscles.

Teres Minor vs. Infraspinatus: Subtle Differences

While both teres minor and infraspinatus externally rotate the shoulder, there are subtle differences. The infraspinatus plays a more dominant role in external rotation, particularly at lower speeds. The teres minor becomes more active during high-speed movements and also contributes to horizontal abduction (moving the arm away from the body in the horizontal plane).

Clinical Significance of Teres Minor Dysfunction

Injury or dysfunction of the teres minor can lead to several problems:

Rotator cuff tears: The teres minor is susceptible to tears, often in conjunction with other rotator cuff muscles. These tears can cause pain, weakness, and limited range of motion.
Shoulder instability: Weakness in the teres minor can compromise shoulder stability, increasing the risk of subluxations or dislocations.
Impingement syndrome: A tight or inflamed teres minor can contribute to impingement syndrome, where the rotator cuff tendons get compressed under the acromion (part of the shoulder blade).
Pain and limited mobility: Pain is a common symptom, often located in the posterior shoulder. This pain can limit the ability to perform daily activities or participate in sports.

Assessing and Treating Teres Minor Dysfunction

Diagnosing teres minor problems requires a thorough physical examination by a healthcare professional. This often involves evaluating range of motion, strength, and palpation of the muscle. Imaging techniques, such as MRI or ultrasound, can confirm the diagnosis, particularly in cases of suspected tears.

Treatment may involve:

Physical therapy: Exercises focusing on strengthening the teres minor and improving shoulder stability are crucial.
Medication: Pain relievers or anti-inflammatory medications can help manage pain and inflammation.
Corticosteroid injections: In some cases, corticosteroid injections may be used to reduce inflammation.
Surgery: In cases of significant tears or persistent dysfunction, surgery might be necessary.

Conclusion: The Importance of Teres Minor

The teres minor, though small, plays a vital role in shoulder function and stability. Understanding its anatomy and action is essential for preventing and treating shoulder injuries. If you experience shoulder pain or weakness, consult a healthcare professional for proper diagnosis and treatment. Remember to always prioritize proper form during any exercises to avoid injury. Proper rehabilitation and preventative strengthening are key to maintaining healthy, strong shoulders.