A 28-year-old man sustains a mid-shaft humeral fracture and presents with wrist drop. Radial nerve injury is suspected. The fracture is managed conservatively. At 8 weeks follow-up, electromyography (EMG) shows fibrillation potentials and positive sharp waves in brachioradialis and extensor carpi radialis longus but no voluntary motor units. What is the most likely Seddon classification of this injury and the expected prognosis?

• A Axonotmesis — spontaneous recovery expected as the endoneural tube is intact; recovery proceeds at ~1mm/day from the injury site ✓
• B Neuropraxia — rapid full recovery expected within 6-8 weeks with no EMG evidence of denervation
• C Neurotmesis — surgical exploration and cable grafting is required immediately as no recovery is possible spontaneously
• D Double crush syndrome — cervical spine MRI needed to identify proximal compression

Explanation

Fibrillation potentials and positive sharp waves on EMG indicate wallerian degeneration (denervation) — ruling out neuropraxia (which causes conduction block without axonal loss, so no fibrillations). The presence of these EMG changes means axonal injury has occurred (axonotmesis or neurotmesis). In the setting of closed mid-shaft humeral fracture managed conservatively, the nerve is almost always in continuity (axonotmesis, Seddon grade II) — the endoneural tubes are intact and guide regenerating axons. Spontaneous recovery occurs at ~1 mm/day (Tinel's sign advancing distally). Neurotmesis (complete division) would require surgical intervention; this is ruled out in a closed fracture without surgical or penetrating injury.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.