Three weeks after a right radical mastectomy with axillary clearance, a patient notices her right scapula protrudes backward when she pushes against a wall. The serratus anterior is weak. Which nerve was injured?

• A Thoracodorsal nerve
• B Long thoracic nerve ✓
• C Medial pectoral nerve
• D Nerve to subclavius

Explanation

The long thoracic nerve (C5, C6, C7) runs on the external surface of serratus anterior in the midaxillary line, exactly where axillary dissection instruments work. Its paralysis denervates serratus anterior, causing medial scapular winging accentuated by wall push-ups. The thoracodorsal nerve is also at risk in this surgery, but it latissimus dorsi weakness causes no scapular winging, which separates it from the key.

Reference: Gray's Anatomy, 42nd ed.

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Written and medically reviewed by the StethoPrep medical team.