A 30-year-old man sustains a humeral shaft fracture and develops wrist drop. At 3 months, nerve conduction studies show no fibrillation potentials and nascent motor units are beginning to appear on EMG. This suggests:

• A Axonotmesis with ongoing axonal regeneration, predicting functional recovery ✓
• B Complete neurotmesis with no recovery expected
• C Neuropraxia with complete recovery expected
• D Chronic denervation with irreversible muscle atrophy

Explanation

The absence of fibrillation potentials (signs of active denervation) combined with the appearance of nascent (newborn) motor unit action potentials (MUAPs) on EMG indicates early reinnervation — axons have regenerated and are reconnecting with muscle fibres. This pattern is characteristic of axonotmesis (Sunderland Grade 2), where the intact endoneurial tubes guide regenerating axons back to their target muscles. The prognosis for functional motor recovery is good. In complete neurotmesis, no nascent MUAPs would appear and fibrillations would persist. In neuropraxia, recovery occurs within weeks (not months) without denervation changes.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.