Anatomy Msk · Year 1 · from Anatomy Msk
Case 2: Spinal Accessory Nerve Injury
Clinical Image
Source: Wikimedia Commons - Spinal Accessory Nerve - CC BY-SA 4.0
Case Presentation
A 48-year-old woman presents with progressive difficulty raising her left arm overhead and chronic aching pain in her left shoulder region 6 weeks after undergoing lymph node biopsy in the posterior triangle of her neck for evaluation of cervical lymphadenopathy. She notes that her shoulder appears to "droop" and she has trouble carrying her purse on that side. Physical examination reveals asymmetry of the shoulders with the left shoulder sitting lower than the right. The left scapula is laterally displaced and rotated, with the inferior angle closer to the spine. When asked to abduct her arm, she has weakness initiating abduction and the scapula wings laterally. Shoulder shrug is weak on the left, and she cannot resist downward pressure on the shoulder. Formal examination reveals weakness of left trapezius muscle (unable to shrug against resistance) with preserved sternocleidomastoid function. EMG/nerve conduction studies confirm spinal accessory nerve injury in the posterior triangle. She is referred for physical therapy focusing on periscapular strengthening and referred to a peripheral nerve surgeon for possible nerve exploration.
Key Learning Points
- The spinal accessory nerve (CN XI) innervates the trapezius and sternocleidomastoid muscles
- The nerve courses superficially through the posterior triangle of the neck, making it vulnerable during surgery
- Trapezius weakness causes shoulder droop, lateral scapular winging, and difficulty with arm abduction above 90 degrees
- The posterior triangle is bordered by the sternocleidomastoid anteriorly, trapezius posteriorly, and clavicle inferiorly
- Iatrogenic injury during lymph node biopsy or neck dissection is a recognized complication