What is subscapularis?

Subscapularis Muscle: Anatomy, Function, Clinical Tests, and Rehabilitation

Introduction

The subscapularis muscle is one of the four rotator cuff muscles of the shoulder and plays a central role in both stability and movement of the joint. Located on the anterior (front) surface of the scapula, it is the largest and strongest rotator cuff muscle, contributing significantly to internal rotation of the humerus. Understanding its anatomy, function, and clinical relevance is essential for healthcare professionals, athletes, and anyone interested in shoulder health.

Anatomy of the Subscapularis Muscle

• Origin: Subscapular fossa on the anterior surface of the scapula

• Insertion: Lesser tubercle of the humerus and anterior capsule of the shoulder joint

• Nerve Supply: Upper and lower subscapular nerves (C5–C7)

• Blood Supply: Subscapular artery and branches of the axillary artery

The subscapularis lies deep in the shoulder, making it less accessible for palpation compared to other rotator cuff muscles.

Functions

The primary functions of the subscapularis include:

• Internal rotation of the shoulder joint

• Adduction of the humerus (bringing the arm toward the body)

• Anterior stabilization of the glenohumeral joint, preventing dislocation

These functions are vital in daily activities such as reaching across the chest, pushing, lifting, and throwing.

Clinical Assessment

Since the subscapularis is deep, direct palpation is limited. Clinicians rely on functional tests:

1. Lift-Off Test (Gerber’s Test):

   • Patient places the dorsum of the hand on the lower back and attempts to lift it off.

   • Inability indicates subscapularis tear or weakness.

2. Belly-Press Test:

   • Patient presses the palm against the abdomen while keeping the elbow forward.

   • Weakness or pain suggests dysfunction.

3. Passive External Rotation:

   • Helps assess tightness or shortening of the muscle.

   • Restricted external rotation can indicate subscapularis contracture.

Common Injuries and Disorders

• Subscapularis Tear: May occur from trauma or repetitive stress.

• Tendinopathy: Often seen in overhead athletes such as swimmers and throwers.

• Impingement Syndrome: The tendon can get compressed beneath the coracoid process.

• Anterior Shoulder Instability: Dysfunction increases risk of dislocation.

Rehabilitation and Exercises

Strengthening Exercises

• Resistance Band Internal Rotation: Standing with the elbow bent at 90°, the patient pulls the band across the body.

• Isometric Internal Rotation: Pressing the palm inward against a wall without moving the arm.

Stretching Exercises

• External Rotation Stretch: Performed lying supine with the shoulder abducted and elbow bent, gently lowering the forearm outward.

These exercises restore strength and flexibility, helping prevent reinjury.

Trigger Points and Pain Patterns

Trigger points in the subscapularis may cause pain in the back of the shoulder, down the arm, or around the wrist. Release techniques and stretching are often used in physiotherapy to manage this condition.

Clinical Importance in Sports

The subscapularis is highly active in sports that involve repetitive arm rotation, such as baseball, tennis, and swimming. Injuries in athletes are common and may limit performance if not managed properly. Early diagnosis and rehabilitation are critical for safe return to play.

Frequently Asked Questions

Q1. What is the main action of the subscapularis muscle?
It is responsible for internal rotation of the humerus at the shoulder joint.

Q2. How do you test the subscapularis muscle clinically?
The Lift-Off Test and Belly-Press Test are the most reliable clinical assessments.

Q3. Can a subscapularis tear heal without surgery?
Mild tears and tendinopathies often respond to physiotherapy and strengthening programs, while large tears may require surgical repair.

Q4. Why is the subscapularis important in athletes?
It stabilizes the shoulder during overhead activities, preventing injuries and maintaining performance.

Q5. How does it differ from other rotator cuff muscles?
The subscapularis is the only internal rotator of the cuff, while the others mainly support external rotation and abduction.

References

1. Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Elsevier; 2021.

2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 7th ed. Wolters Kluwer; 2013.

3. Burkhart SS, Tehrany AM. Arthroscopic subscapularis tendon repair: Technique and results. Arthroscopy. 2002;18(5):454-463.

4. Escamilla RF et al. Shoulder muscle activity in common rehabilitation exercises. Sports Med. 2009;39(8):663-685.