During a radical neck dissection, the spinal accessory nerve (CN XI) is sacrificed in the posterior triangle. Which specific functional deficit is the hallmark of this injury?
- A Inability to shrug the shoulder and weak arm abduction beyond 90 degrees ✓
- B Inability to turn the head to the opposite side
- C Paralysis of the diaphragm on the same side
- D Loss of sensation over the angle of the mandible
Correct answer: A. Inability to shrug the shoulder and weak arm abduction beyond 90 degrees
Explanation
The spinal accessory nerve (CN XI) innervates the trapezius muscle. Injury causes inability to shrug the shoulder and inability to abduct the arm beyond 90 degrees, since trapezius is required for scapular rotation. Sternocleidomastoid injury causes inability to turn the head to the opposite side. Diaphragm paralysis is from phrenic nerve (C3-C5) injury.
Reference: Gray's Anatomy for Students, 4th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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