A 28-year-old man sustains a gunshot wound to the axilla. EMG at 4 weeks shows fibrillations in the biceps but normal SNAP (sensory nerve action potential) in the musculocutaneous nerve territory. The Seddon/Sunderland classification implied is:

• A Neuropraxia (Sunderland I) — segmental demyelination, no axonal injury
• B Axonotmesis (Sunderland II) — axonal continuity lost, endoneurium intact, complete Wallerian degeneration ✓
• C Neurotmesis (Sunderland V) — complete nerve trunk division
• D Sunderland III — axon and endoneurium disrupted, perineurium intact

Explanation

Fibrillations on EMG at 4 weeks indicate Wallerian degeneration of motor axons (axonotmesis or worse) — ruling out neuropraxia. Normal SNAP indicates sensory axons peripheral to the lesion are viable, which occurs in both Sunderland II (axonotmesis with intact endoneurium) and preganglionic lesions; however, gunshot wound is a closed penetrating injury, not an avulsion, making Sunderland II (axonotmesis) the most likely. In axonotmesis, the endoneurial tube is intact, allowing accurate axonal regrowth at ~1–3 mm/day (1 inch/month) and full recovery is expected without surgical repair. Neurotmesis (Sunderland V) requires surgical repair and SNAP would be absent due to DRG disconnection.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.