action of teres minor

3 min read 18-03-2025

The teres minor is a small, yet significant, muscle located in the posterior shoulder. Understanding its anatomy and function is crucial for diagnosing and treating a variety of shoulder conditions. This article will delve into the details of the teres minor muscle, exploring its action, innervation, and clinical significance.

Anatomy of the Teres Minor

The teres minor is one of the four rotator cuff muscles, a group of muscles and tendons that surround the shoulder joint. It's situated inferior to the infraspinatus muscle and superior to the teres major muscle. As its name suggests, it's smaller than the teres major.

Origin: The lateral border of the scapula (shoulder blade).
Insertion: The greater tubercle of the humerus (upper arm bone).
Innervation: The axillary nerve (C5-C6).

The teres minor's close proximity to other rotator cuff muscles means it often works in coordination with them to provide stability and control to the shoulder joint.

Action of the Teres Minor: External Rotation and Stabilization

The primary action of the teres minor is external rotation of the humerus. This means it helps to rotate the arm away from the body. This action is crucial for a wide range of movements, from throwing a ball to reaching overhead.

However, its role extends beyond just external rotation. The teres minor also contributes to:

Shoulder joint stability: Along with other rotator cuff muscles, it helps to stabilize the humeral head within the glenoid fossa (the socket of the shoulder joint). This stability is critical for preventing dislocation and injury.
Adduction of the humerus: To a lesser extent, the teres minor assists in adduction, or bringing the arm closer to the body.
Horizontal abduction: Assists in moving the arm away from the midline of the body when the arm is already abducted to 90 degrees.

The teres minor's synergistic action with the infraspinatus further enhances its role in external rotation and shoulder stabilization.

Synergistic Muscles and Antagonistic Muscles

The teres minor works synergistically with the infraspinatus muscle in performing external rotation of the shoulder joint. Both muscles are innervated by the axillary nerve, contributing to coordinated movement.

Antagonistic muscles, those that perform the opposite action, to the teres minor include the subscapularis and pectoralis major, primarily responsible for internal rotation.

Clinical Relevance of the Teres Minor

Injuries to the teres minor, such as tears or strains, can significantly impact shoulder function. These injuries can result from:

Repetitive overhead movements: Activities like throwing, swimming, or weightlifting.
Sudden trauma: A fall or direct blow to the shoulder.
Degenerative changes: Age-related wear and tear on the muscle and tendon.

Symptoms of a teres minor injury may include:

Pain in the back of the shoulder: The pain may radiate down the arm.
Weakness in external rotation: Difficulty rotating the arm away from the body.
Limited range of motion: Restricted movement in the shoulder joint.

Diagnosis typically involves a physical examination and imaging studies like MRI or ultrasound. Treatment options may include rest, ice, physical therapy, and in some cases, surgery.

Strengthening the Teres Minor

Strengthening the teres minor and other rotator cuff muscles can help prevent injuries and improve shoulder stability. Exercises that focus on external rotation, such as:

External rotation with resistance band: Holding a resistance band, externally rotate your arm against the resistance.
Side-lying external rotation: Lie on your side and externally rotate your arm.
Scaption with external rotation: Raise your arm to shoulder height and externally rotate.

These exercises should be performed under the guidance of a physical therapist or qualified professional, especially after an injury.

Conclusion

The teres minor, although a relatively small muscle, plays a crucial role in shoulder function. Understanding its anatomy, action, and clinical relevance is important for healthcare professionals and individuals alike. By strengthening this muscle and taking preventative measures, you can contribute to the overall health and stability of your shoulder joint. Remember to consult a healthcare professional for any concerns regarding shoulder pain or injury.