During a modified radical mastectomy with axillary node dissection, the surgeon identifies the long thoracic nerve (nerve of Bell) on the serratus anterior. Injury to this nerve causes which deformity on clinical examination?

• A Lateral winging of the scapula — inferior angle rotates laterally
• B Dropped shoulder with inability to abduct the arm beyond 90°
• C Medial winging of the scapula — scapula displaced medially with the inferior angle rotating medially on pushing the hand against a wall ✓
• D Loss of arm adduction at the shoulder

Explanation

The long thoracic nerve (C5, C6, C7) supplies serratus anterior, which holds the scapula against the thoracic wall and rotates the inferior angle laterally/upward during arm elevation. Injury causes 'medial winging': the serratus anterior can no longer keep the medial border and inferior angle of the scapula against the thoracic wall, so when the patient pushes against a wall the scapula's medial border wings out posteriorly and the inferior angle shifts medially. This contrasts with lateral winging (from trapezius weakness/spinal accessory nerve injury) where the inferior angle rotates laterally. Long thoracic nerve injury also limits arm elevation beyond ~120° as scapular rotation is impaired.

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

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Written and medically reviewed by the StethoPrep medical team.