Mechanical injuries to peripheral nerves occur because of compression, entrapment, transection, laceration, ischemia, crushing, stretching, or chemical or burn damage. Neurapractic lesions are characterized by a failure of conduction of the action potential across the injured axonal segment. Axonotmesis is axonal interruption, while neurotmesis reflects disruption of endoneurium, perineurium, and/or epineurium. Recovery by axonal regrowth is unlikely after neurotmesis. After axonotmesis of motor nerves, muscle reinnervation occurs by 2 separate mechanisms: collateral sprouting and axonal regrowth. If there is incomplete loss of axons , reinnervation of muscle units by sprouting occurs in days to weeks. Reinnervation by axonal regrowth occurs at a rate of 1 mm per day (approximately 1 inch/month). Reinnervation may not be possible after more than 12 months although this remains a controversial issue. Peripheral nerve injuries are characterized by weakness of the innervated muscle accompanied within2-4 weeks by appreciable atrophy.
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