• Class I (first degree) injury (Neuropraxia): loss of axoplasmic flow from compression of the axon results in only a conduction block, complete recovery anticipated
• Class II (second degree) injury (Axonotmesis): axon disrupted, endoneurium preserved, wallerian degeneration occurs distal to site of injury, complete recovery anticipated (axon regenerates through an intact neural tube at 1 mm/day)
• Class III (third degree) injury (Neurotmesis): neural tube (axons, myelin sheath, and endoneurium) disruption, wallerian degeneration occurs distal to site of injury, unpredictable outcome (loss of endoneural tubules results in high risk for synkinesis, the contraction of multiple muscle fibers simultaneously, if regrowth occurs)
• Class IV (fourth degree) injury: violates perineurium
• Class V (fifth degree) injury: complete transection, risk of a neuroma from nerve sprouts outside of nerve sheath
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