The long thoracic nerve (nerve of Bell) is vulnerable during axillary lymph node dissection in breast cancer surgery. Which muscle does it supply, and what deformity results from its injury?

• A Trapezius; lateral winging of the scapula with shoulder drooping
• B Rhomboids; medial winging with difficulty retracting the scapula
• C Serratus anterior; medial winging of the scapula aggravated by pushing the arm forward against resistance ✓
• D Latissimus dorsi; difficulty adducting and extending the shoulder

Explanation

The long thoracic nerve (C5, C6, C7) supplies the serratus anterior, which protracts and rotates the scapula upward during arm elevation. Injury during axillary dissection causes medial winging of the scapula (the medial border lifts away from the chest wall), which is most prominent when the patient pushes the outstretched arm against a wall. Trapezius palsy (spinal accessory nerve) causes lateral winging. Rhomboid weakness (dorsal scapular nerve) also causes medial winging but is worsened by retraction, not forward pushing. The distinction is clinically important in post-mastectomy rehabilitation.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.