Surgery MCQs Q20

A 40-year-old woman undergoes a radical mastectomy. Postoperatively, she loses the ability to fold her right arm behind the back and to reach the opposite scapula.

👉 Question:
Which nerve is most likely injured?

Options:
A. Medial pectoral nerve
B. Long thoracic nerve
C. Thoracodorsal nerve
D. Subscapular nerve
E. Suprascapular nerve

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✅ Correct Answer:
C. Thoracodorsal nerve

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📚 Explanation:

• C. ✅ The thoracodorsal nerve (middle subscapular nerve) innervates the latissimus dorsi muscle. Injury leads to inability to adduct, extend, and internally rotate the arm, particularly noticeable when trying to fold the arm behind the back or reach opposite scapula, as seen after radical mastectomy or axillary dissection.
• A. Medial pectoral nerve ❌ – Innervates pectoralis minor and part of pectoralis major; injury weakens shoulder adduction but does not prevent reaching behind the back.
• B. Long thoracic nerve ❌ – Injury causes winged scapula due to serratus anterior paralysis; patient can still reach behind the back.
• D. Subscapular nerve ❌ – Innervates subscapularis and teres major; injury impairs internal rotation but does not severely limit reaching behind the back.
• E. Suprascapular nerve ❌ – Innervates supraspinatus and infraspinatus; injury causes difficulty with abduction and external rotation, not folding arm behind back.

🧠 High-Yield Points:

• 💡 Thoracodorsal nerve injury → loss of latissimus dorsi function.
• 💡 Function affected: arm extension, adduction, internal rotation; difficulty reaching behind the back.
• 💡 Common cause: axillary node dissection during radical mastectomy.
• 💡 Long thoracic nerve injury → winged scapula; differentiate from thoracodorsal nerve injury.

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📖 Read Related Topic:

Click here for full topic: Thoracodorsal Nerve Injury – Post-Mastectomy Complications

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