Question 1

Question

A 28-year-old woman undergoes excision of an enlarged lymph node in the posterior triangle of the neck. Two weeks post-operatively she is unable to shrug her left shoulder. Nerve conduction studies confirm injury to the arrowed nerve (Image 1) as well as a separate injury to the long thoracic nerve, accounting for a newly noted winged scapula on the ipsilateral side. Which of the following best explains why TWO distinct nerve injuries are required to account for both motor deficits observed in this patient?

Accepted Answer

D. The arrowed nerve (CN XI) supplies only the trapezius and sternocleidomastoid; serratus anterior is innervated exclusively by the long thoracic nerve (C5–C7), so injury to both nerves is necessary to produce the combined deficit of shoulder-shrug weakness and winged scapula

Answer

A. The arrowed nerve supplies both the trapezius and the serratus anterior, travelling superficially across the posterior triangle before piercing the deep cervical fascia

Answer

B. The arrowed nerve supplies the trapezius directly and communicates with the long thoracic nerve within the posterior triangle, jointly innervating serratus anterior

Answer

C. The arrowed nerve supplies the trapezius, and a separate branch arising at the same level in the posterior triangle independently innervates serratus anterior

Functional Anatomy — MCQs

Functional Anatomy — MCQs

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