Teres Minor
- Fysiobasen
- 4 days ago
- 9 min read
Teres minor is a small but important muscle located on the posterior aspect of the shoulder. It is part of the rotator cuff – a group of muscles that stabilize the shoulder joint and enable precise movements. The muscle runs from the scapula and inserts onto the humerus.
Origin and Insertion
The origin of teres minor is:
• The upper two-thirds of the lateral border on the posterior surface of the scapula, known as the lateral border of the scapula or margo lateralis scapulae.
This area is rough and elongated, and the origin itself is divided into two parts by a small vascular groove through which the circumflex scapular artery passes⠀
The two separate parts of the muscle quickly merge into a single muscle belly that runs in a superolateral direction—upwards and outwards—towards the upper arm.
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The insertion of the muscle is:
• The upper part of the greater tubercle of the humerus, more specifically the inferior facet of this bony prominence.
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The superior muscle fibres end in a distinct tendon that attaches to this facet.
The inferior muscle fibres insert immediately below this area, directly onto the bone of the proximal humeral shaft, between the tendinous insertion and the origin of the lateral head of the triceps brachii.
This dual insertion provides strong anchorage to the humerus and allows teres minor to transfer force effectively and contribute to precise movements of the shoulder.
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Nerve Supply
Teres minor receives its nerve supply from:
• The axillary nerve, also known as nervus axillaris.
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This nerve originates from the posterior cord of the brachial plexus and contains nerve fibres from the C5 and C6 spinal nerve roots.
After passing through the quadrangular space, it gives off branches to both the deltoid and teres minor.
The location of the nerve in relation to the muscle means that injury to the axillary nerve—for example, following a shoulder dislocation—can often lead to impaired teres minor function. Clinically, this may present as weakness during external rotation or a positive Hornblower’s sign.
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Blood Supply
The blood supply to teres minor is primarily provided by:
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• The circumflex scapular artery, a branch of the subscapular artery.
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• The posterior circumflex humeral artery, a branch of the third part of the axillary artery.
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These two arteries form anastomoses around the scapula and posterior shoulder region, ensuring an adequate blood supply even when one of the supplying vessels is partially obstructed.
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Some anatomical variation exists. In certain individuals, smaller branches of the suprascapular artery may also contribute to the capillary circulation of the muscle. This overlapping blood supply is clinically relevant during surgical procedures involving the posterior shoulder and when assessing the healing potential of the rotator cuff following a tear.
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Function and Role in the Shoulder Joint
Teres minor is one of the four rotator cuff muscles. Although it is smaller than the others, it plays an essential role in shoulder stability and precise movement. The muscle is located posteriorly and provides mechanical support to the posterior aspect of the glenohumeral joint capsule.
Its primary functions are:
• External rotation of the upper arm, particularly when the arm is positioned alongside the body.
• Adduction of the upper arm, especially from an elevated position, such as when lowering the arm from above the head.
• Joint stabilisation: Together with the other rotator cuff muscles, teres minor compresses the humeral head into the glenoid cavity. This helps prevent excessive translation or dislocation, particularly during rapid or forceful arm movements.
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These functions make teres minor particularly important during activities that require precise force production in end-range positions, including throwing, swimming, climbing and heavy work performed with the arms behind the body.
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Cooperation With Other Muscles
Teres minor frequently works in close cooperation with infraspinatus, which is also an external rotator of the shoulder. However, while infraspinatus covers a larger area and produces more force, teres minor provides more refined and precise control.
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In certain situations, such as injury to infraspinatus, teres minor may partially compensate for the loss of function. However, its capacity to compensate independently is limited.
It also works together with:
• Teres major, latissimus dorsi and pectoralis major during adduction of the arm.
• Subscapularis and the deltoid as part of the dynamic balance and muscular synergies of the rotator cuff.
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Anatomical Relationships and Location
Teres minor is located in close proximity to several structures and muscles. Its anatomical position is important for both function and clinical assessment.
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Important anatomical relationships include:
• Superiorly: Infraspinatus.
• Inferiorly: Teres major.
• Medially: The long head of the triceps brachii.
• Laterally and anteriorly: The humerus and the shoulder joint capsule.
• Superficially: The deltoid.
• Deeper, towards the thoracic wall: The trapezius and parts of the scapula.
The muscle also forms important boundaries within the posterior axillary region:
• Quadrangular space: Teres minor forms the superior border. The axillary nerve and posterior circumflex humeral artery pass through this space from the anterior to the posterior aspect of the shoulder.
• Triangular space: Teres minor forms the superior border, and the circumflex scapular artery passes through this space.
Understanding these anatomical relationships is clinically important when assessing or managing:
• Nerve compression, including quadrangular space syndrome.
• Posterior surgical approaches to the shoulder.
• Tendon injuries and compression syndromes.
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Specific Considerations During Loading and Movement
When the arm is elevated and rotated, such as during throwing or overhead work, teres minor works eccentrically after the primary movement has been performed.
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This means that the muscle lengthens while producing force to decelerate the movement in a controlled manner. This reduces the risk of overstretching or injuring the joint capsule and surrounding tendons.
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This function also makes teres minor vulnerable to overuse and microscopic tissue damage, particularly among athletes who frequently perform overhead movements.
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Injuries and Load-Related Disorders
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Although teres minor is rarely injured in isolation, it may be affected by several clinical conditions. It may be involved as part of a larger rotator cuff injury or as a result of overuse, nerve impairment or degenerative changes.
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The most common clinical conditions include:
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• Rotator cuff tears: In massive rotator cuff tears, teres minor may be the only intact muscle contributing to external rotation. Isolated degeneration of teres minor may also occur in older adults, particularly following prolonged inactivity.
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• Quadrangular space syndrome: This is a rare condition in which neural and vascular structures, particularly the axillary nerve and posterior circumflex humeral artery, are compressed within the quadrangular space behind the shoulder. It may cause pain, paraesthesia and weakness, particularly in the deltoid and teres minor.
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• Fatty infiltration and atrophy: Prolonged inactivity or nerve injury, such as axillary nerve impairment following trauma or surgery, may lead to fatty infiltration of teres minor. This can be clearly identified on MRI and may result in functional impairment.
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• Tendinopathy: Repetitive external rotation and overhead activities, such as tennis, volleyball, swimming and throwing, may cause chronic tendon overload even without a tear. This often produces diffuse, deep pain in the posterior shoulder.
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Typical Symptoms of Teres Minor Dysfunction
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• Reduced strength during external rotation of the shoulder, particularly with the arm positioned in 90 degrees of abduction.
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• Deep, aching pain in the posterior aspect of the shoulder.
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• Reduced force during specific throwing movements.
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• Difficulty stabilising the arm during external rotation and elevation.
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Assessment and Testing
The most widely recognised test of teres minor function is Hornblower’s sign, which is also referred to as the Patte test.
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Hornblower’s Sign
• Purpose: To assess the function of teres minor and, to some extent, infraspinatus.
• Procedure: The patient elevates the arm to 90 degrees of abduction in the scapular plane while keeping the elbow flexed to 90 degrees. The examiner applies resistance against external rotation.
• Interpretation: The test is considered positive when the patient is unable to produce or maintain external rotation and the arm falls into internal rotation. This may indicate weakness or tearing of teres minor.
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Differential Diagnoses
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• Infraspinatus tear.
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• Supraspinatus or subscapularis lesions.
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• Cervical radiculopathy involving the C5 or C6 nerve roots.
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• Posterior or posterosuperior shoulder impingement.
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• Adhesive capsulitis, also known as frozen shoulder.
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Treatment and Rehabilitation
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Treatment of teres minor-related disorders generally follows the established principles of rotator cuff rehabilitation.
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Relevant interventions may include:
• Load modification and pain management during the acute stage.
• Specific strengthening of the external rotators, with an emphasis on isolated strengthening and movement control in the scapular plane.
• Neuromuscular control exercises using low resistance and a relatively high number of repetitions to challenge coordination and stability.
• Manual therapy and joint mobilisation when secondary stiffness or capsular restrictions are present.
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In cases involving a teres minor tear, surgical reconstruction is generally considered only when the functional impairment is substantial and the patient has high physical demands.
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In most cases, infraspinatus and the surrounding structures can compensate for some of the lost function.
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Exercises for Teres Minor
Teres minor is a small but important muscle for shoulder stability and external rotation. It works closely with infraspinatus but may be targeted more effectively through carefully selected positions and loading strategies.
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Training teres minor is particularly relevant during rehabilitation following rotator cuff injuries, for the prevention of shoulder disorders and for athletes who require good control of external rotation, including those participating in throwing sports, swimming and climbing.
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What Does the Research Show?
Electromyographic studies have shown that completely isolating teres minor from infraspinatus is challenging. However, certain exercises appear to produce greater activation in the distal and lateral portion of the rotator cuff, where teres minor is located.
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In a study by Reinold et al. (2004), external rotation performed with the shoulder abducted, as well as exercises performed in the prone position, produced considerable activation of teres minor compared with more general shoulder exercises.
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Training Objectives
• Increase strength and muscular endurance in the external rotators of the shoulder.
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• Improve fine motor control and dynamic stability.
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• Reduce excessive dominance of larger muscles such as the deltoid and latissimus dorsi.
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• Strengthen teres minor in functional positions involving abduction and overhead movement.
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Effective Exercises for Teres Minor
1. Side-Lying External Rotation
• Procedure: Lie on your side with the elbow flexed to 90 degrees. Hold a light dumbbell and rotate the forearm upwards into external rotation.
• Focus: This is a classic rotator cuff exercise that recruits both infraspinatus and teres minor. To potentially increase the contribution of teres minor, the elbow may be positioned slightly above the level of the torso.
• Variation: Use a resistance band to provide more consistent resistance throughout the movement.
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2. Prone Horizontal Abduction With External Rotation
• Procedure: Lie face down with the arms positioned out to the sides in 90 degrees of abduction. Point the thumbs upwards and gently lift the arms while maintaining external rotation.
• Research: This exercise may produce high EMG activity in both infraspinatus and teres minor when the starting position is adjusted to limit excessive deltoid dominance.
• Tip: Begin without additional resistance and gradually add a weight of approximately 0.5–1 kilogram when appropriate.
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3. Cable External Rotation at 90 Degrees of Abduction
• Procedure: Stand or sit with the upper arm positioned in 90 degrees of abduction and the elbow flexed to 90 degrees. Rotate the forearm backwards against resistance from a cable machine or resistance band.
• Benefit: This position may activate teres minor more effectively than external rotation performed with the arm alongside the body.
• Progression: Gradually increase the resistance while maintaining stable scapular positioning.
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4. Wall Slides With External Rotation
• Procedure: Stand facing a wall with the forearms against the wall and the elbows flexed to approximately 90 degrees. Slide the arms upwards while gently pressing the wrists backwards to maintain external rotation.
• Effect: The exercise activates the stabilising muscles of the shoulder and may improve proprioception and control of teres minor and infraspinatus.
• Application: This exercise can be used as part of a warm-up before shoulder loading during sport or strength training.
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5. Cuban Press
• Procedure: Begin by holding dumbbells in front of the body. Raise the upper arms to approximately 90 degrees of abduction, rotate the forearms upwards through controlled external rotation and then press the weights overhead.
• Benefit: The exercise combines several joint positions in which teres minor must contribute to shoulder stability.
• Important: The Cuban press requires adequate shoulder mobility and should be avoided or modified in the presence of impingement symptoms or pain.
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Tips for Optimal Effect
• Begin with frequent, low-load training: Many patients and athletes have reduced muscular control or excessive deltoid dominance. Training should therefore initially involve low resistance and a relatively high number of repetitions, such as 12–20 repetitions
• Prioritise technique: An inappropriate movement angle or compensation through the trapezius may reduce the contribution of teres minor.
• Use bilateral variations: Include both unilateral and bilateral exercises. A mirror may also be used to provide visual biofeedback.
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Summary of Clinical Significance
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• Teres minor is small but highly important for posterior shoulder stability and refined motor control.
• It is particularly vulnerable during throwing sports and following trauma to the shoulder.
• Isolated injuries are uncommon but may be clinically significant in patients with persistent shoulder dysfunction.
• Hornblower’s sign is a simple and clinically useful test for impaired teres minor function.
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Sources
Cael, C. (2010). Functional anatomy: Musculoskeletal anatomy, kinesiology, and palpation for manual therapists. Philadelphia, PA: Wolters Kluwer Health/Lippincott, Williams & Wilkins.
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Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically oriented anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.
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Netter, F. H. (2019). Atlas of human anatomy (7th ed.). Philadelphia, PA: Saunders.
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Palastanga, N., & Soames, R. (2012). Anatomy and human movement: Structure and function (6th ed.). Edinburgh: Churchill Livingstone.
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Standring, S. (Ed.). (2016). Gray’s anatomy: The anatomical basis of clinical practice (41st ed.). Edinburgh: Elsevier Churchill Livingstone.
