Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

 

Rotator Cuff Muscles

Overview

• The rotator cuff is a group of four muscles:
  • Supraspinatus
  • Infraspinatus
  • Teres Minor
  • Subscapularis
• Common Features:
  • All muscles originate from the scapula
  • Insert into the proximal humerus
  • Function to stabilize the shoulder joint

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1. Supraspinatus

Origin & Insertion

• Origin: Supraspinous fossa of the scapula
• Insertion: Superior facet of the greater tubercle of the humerus

Function

• Initiates abduction of the arm
• Helps stabilize the humeral head

Nerve Supply

• Suprascapular nerve (C5, C6)
• Arises from the superior trunk of the brachial plexus

Clinical Significance

• Tear leads to:
  • Inability to abduct the shoulder

Clinical Tests

• Neer Impingement Test
• Hawkins Test
• Jobe’s (Empty Can) Test
  • Shoulder abducted to 90°
  • Flexed to 30°
  • Internally rotated
  • Downward resistance applied

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2. Infraspinatus

Origin & Insertion

• Origin: Infraspinous fossa of the scapula
• Insertion: Middle facet of the greater tubercle of the humerus

Function

• Primary external rotator of the arm
• Assists in shoulder stabilization

Nerve Supply

• Suprascapular nerve (C5, C6)

Clinical Significance

• Tear results in:
  • Weakness in external rotation

Clinical Tests

• External Rotation Against Resistance
• External Rotation Lag Test
  • Arm placed in full external rotation
  • Positive if patient cannot maintain position

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3. Teres Minor

Origin & Insertion

• Origin: Lateral border of the scapula
• Insertion: Greater tubercle of the humerus

Function

• Assists in external rotation of the arm
• Works with infraspinatus

Nerve Supply

• Axillary nerve (C5, C6)
• From the posterior cord of the brachial plexus

Clinical Tests

• Hornblower’s Test
  • Arm held in 90° abduction
  • Positive if arm falls into internal rotation

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4. Subscapularis

Origin & Insertion

• Origin: Subscapular fossa
• Insertion:
  • Lesser tubercle of the humerus
  • Anterior shoulder capsule

Function

• Internal rotation of the arm
• Assists in adduction
• Stabilizes the shoulder joint

Nerve Supply

• Upper and Lower Subscapular Nerves (C5, C6, C7)
• From the posterior cord

Clinical Tests

• Lift-Off Test
  • Inability to lift hand off lower back ? positive
• Lag Sign
  • Inability to maintain hand away from back
• Belly Press Test
  • Positive if:
    • Wrist flexes OR
    • Elbow drops posteriorly

Clinical Significance

• Tear leads to:
  • Weak internal rotation
  • Difficulty with hand-behind-back movements

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Summary

• Rotator cuff muscles are essential for:
  • Shoulder stability
  • Arm rotation and movement
• Each muscle has:
  • Specific function
  • Distinct clinical tests
• Early diagnosis of tears is crucial for optimal shoulder function