A patient with a posterior triangle lymph node biopsy develops inability to abduct the shoulder beyond 90 degrees with winging of the shoulder. Which nerve is at risk in the posterior triangle of the neck?

• A Long thoracic nerve
• B Suprascapular nerve
• C Dorsal scapular nerve
• D Accessory nerve (CN XI) ✓

Explanation

The accessory nerve (CN XI) crosses the posterior triangle superficially, making it vulnerable to damage during lymph node biopsy or neck dissection. It supplies the sternocleidomastoid and trapezius muscles. Trapezius paralysis impairs shoulder elevation, causes inability to abduct the shoulder above 90 degrees (trapezius needed for superior rotation of scapula beyond 90°), and produces lateral/shoulder winging of the scapula. The long thoracic nerve is in the axilla and causes medial winging.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.