What is infraspinatus muscle?

Infraspinatus Muscle: Anatomy, Function, Clinical Assessment & Rehab

Introduction

The infraspinatus muscle is a key component of the rotator cuff, playing a vital role in shoulder stability and external rotation of the humerus. Understanding this muscle is essential for clinicians, physiotherapists, athletes, and students of anatomy. Dysfunction or injury to the infraspinatus is common in overhead athletes, manual workers, and individuals with poor posture or degenerative shoulder conditions.

Anatomy of Infraspinatus

Origin

  • Medial two-thirds of the infraspinous fossa of the scapula.

Insertion

  • Middle facet of the greater tubercle of the humerus.

Nerve Supply

  • Suprascapular nerve (C5, C6).

Blood Supply

  • Suprascapular artery, with contributions from the circumflex scapular artery.

Function of the Infraspinatus

  • External rotation of the shoulder joint (humerus).

  • Stabilization of the glenohumeral joint by compressing the humeral head into the glenoid fossa.

  • Assists in horizontal abduction during arm movement.

Palpation Technique

  1. Ask the patient to sit with their arm resting on their thigh.

  2. Locate the spine of the scapula and move just inferiorly.

  3. Ask the patient to gently externally rotate the shoulder.

  4. The muscle belly beneath your fingers will contract and is felt just below the scapular spine.

Muscle Testing

Power/Strength Testing

  • Patient is seated or prone.

  • Arm abducted to 90° and elbow flexed to 90°.

  • Ask the patient to externally rotate the arm against resistance.

  • Weakness may suggest infraspinatus tear or suprascapular nerve involvement.

Length Testing

  • Place the arm across the chest with the shoulder internally rotated.

  • Limited passive external rotation could indicate tightness or fibrosis of the infraspinatus.

Common Injuries and Conditions

  • Infraspinatus tendinopathy

  • Rotator cuff tears (partial or full-thickness)

  • Suprascapular nerve entrapment

  • Myofascial pain syndrome

  • Shoulder impingement syndrome

Rehabilitation and Strengthening Exercises

1. Side-Lying External Rotation

  • Position: Lie on the unaffected side, elbow flexed to 90°.

  • Procedure: Hold a light dumbbell and externally rotate the arm keeping elbow tucked to the body.

2. Resistance Band External Rotation

  • Position: Standing with elbow bent at 90°, upper arm close to body.

  • Procedure: Pull the band outward while maintaining elbow position.

3. Isometric External Rotation

  • Position: Standing with the elbow at 90°.

  • Procedure: Press the hand outward against a wall or therapist’s hand without actual movement.

Perform 2–3 sets of 10–15 repetitions as tolerated. Ensure no pain during exercise.

Trigger Points

  • Found in the middle of the infraspinatus belly.

  • Pain often radiates to the anterior deltoid, biceps, or lateral forearm.

  • Can mimic cervical radiculopathy.

  • Dry needling or ischemic compression may relieve symptoms.

Clinical Significance

  • Essential to assess in patients with shoulder pain, throwing injuries, or chronic instability.

  • Infraspinatus dysfunction is often confused with posterior deltoid or teres minor involvement.

  • Delayed diagnosis can lead to muscle atrophy, fatty infiltration, and poor surgical outcomes in rotator cuff tears.

FAQs About the Infraspinatus Muscle

1. How can I tell if my infraspinatus is weak?

Weakness during external rotation, especially when tested with resistance, often points to infraspinatus dysfunction. Other signs include difficulty throwing, reaching backward, or shoulder instability.

2. Can infraspinatus muscle pain refer to the arm?

Yes, trigger points in the infraspinatus often refer pain to the front of the shoulder, upper arm, and even the hand in some cases.

3. How do you treat infraspinatus tendinopathy?

Conservative treatment includes rest, ice, NSAIDs, manual therapy, and gradual strengthening. In severe cases, injections or surgical intervention may be needed.

4. What sports commonly cause infraspinatus injuries?

Baseball, tennis, swimming, volleyball, and cricket—essentially any sport involving overhead movements.

5. Can poor posture affect infraspinatus function?

Yes, rounded shoulders and forward head posture increase the load on the rotator cuff, including the infraspinatus, leading to overuse injuries.

References

  1. Neumann, D. A. (2010). Kinesiology of the Musculoskeletal System. Elsevier.

  2. Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2013). Clinically Oriented Anatomy. Lippincott Williams & Wilkins.

  3. Kendall, F. P., McCreary, E. K., & Provance, P. G. (2005). Muscles: Testing and Function with Posture and Pain. Lippincott.

  4. Travell, J. G., & Simons, D. G. (1999). Myofascial Pain and Dysfunction: The Trigger Point Manual. Williams & Wilkins.

  5. Magee, D. J. (2008). Orthopedic Physical Assessment. Elsevier Health Sciences.


Location: United States

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