A 40-year-old woman develops lateral scapular winging after lymph node biopsy in the posterior triangle of the neck. She cannot abduct the arm above 90 degrees because of inability to rotate the scapula upward. Which muscle is denervated?

• A Trapezius ✓
• B Serratus anterior
• C Rhomboid major
• D Latissimus dorsi

Explanation

The spinal accessory nerve traverses the posterior triangle of the neck and is at risk during lymph node biopsy. Denervation of trapezius causes lateral winging of the scapula and loss of upward rotation, limiting overhead abduction. Serratus anterior weakness produces medial winging that worsens on forward push, not on abduction, which distinguishes it from this pattern. Rhomboids are supplied by the dorsal scapular nerve and cause mild medial winging when weak.

Reference: Gray's Anatomy for Students, 4th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.