A 28-year-old sustains a mid-shaft humerus fracture in a road traffic accident. One month later, electrodiagnostic studies show absent sensory nerve action potentials and fibrillation potentials in the radial nerve territory. What is the Seddon classification of this injury and what does the electrodiagnostic pattern indicate?

• A Neuropraxia; the nerve sheath is intact with temporary conduction block — complete recovery expected
• B Neurotmesis; complete nerve transection requiring surgical repair
• C Neuropraxia; fibrillations indicate impending recovery of conduction
• D Axonotmesis; axonal continuity is disrupted with endoneurial tube intact, causing Wallerian degeneration — fibrillations indicate denervation ✓

Explanation

Absent SNAPs with fibrillation potentials at 3–4 weeks post-injury indicate Wallerian degeneration of the axons distal to the injury — consistent with axonotmesis (Seddon) or Sunderland grades 2–4. In neuropraxia (Sunderland grade 1), the axon is intact, there is no Wallerian degeneration, no fibrillations, and SNAPs are preserved. Fibrillations represent spontaneous discharges of denervated muscle fibres and confirm axon loss. In axonotmesis, the endoneurial tube is intact, allowing guided regeneration at ~1–2 mm/day with good prognosis.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.