In the peripheral nervous system, nerves can regenerate; however, recovery of motor function is time sensitive.
TIME IS MUSCLE with 4th and 5th degree nerve injury (complete scarring and nerve transection injuries).
If you miss the period when a motor end organ can be reinnervated (within one year of injury if the nerve is completely in discontinuity with the muscle fibers), then you will be unable to regain function in that particular muscle by any procedure attempting to reinnervate because the muscle will not respond.
Timeline of treatment varies by type of injury (open/closed/gunshot wound) and by time of presentation of the patient. Preferably, you see patient at time of injury, then monthly until treatment decision has been made or recovery has occurred.
Nerves that have undergone Wallerian degeneration due to crush, traction, or open injury will need to regenerate down the appropriate path from the point of injury distally (at approximately 1 mm/day, or 1 inch/month) until the end organ is reached.
Key examples by injury type:
• Open injury with loss of distal function -- generally something should be done involving reinnervation:
• If it is early enough/close enough to the motor end plate to reach in the expected recovery time, consider direct/interposed graft repair.
• If options are limited for nerve transfer (e.g., multiple nerves are injured), consider direct/interposed graft repair.
• If faster reinnervation is desired, and some loss of donor nerve function is available and reasonable, consider nerve transfer.
• Closed nerve injury with no evidence of recovery at 3 months post-injury -- consider reinnervation strategies (see above for options).
• Complex closed injuries (such as complete brachial plexus) and gun shot wound injuries with evidence of progressive recovery (by history, exam and electrodiagnostic testing) -- often better treated with continued non-surgical treatment strategies. If recovery seems to be slowed (static Tinel’s sign) at a specific site of known nerve compression, especially distal to the main injury site, consider decompression procedures.
Key examples by timing of presentation:
• Acute presentation of a nerve injury:
• Needs exam as soon as possible to allow tracking of initial deficits and subsequent return of function (if present).
• Open nerve transection injuries should be managed with acute (usually non-emergent) exploration and treatment.
• Gunshot wounds usually do not have true direct nerve transection and should be managed like closed nerve injuries -- follow over time before treatment decisions are made.
• Subacute presentation of a nerve injury:
• If early enough, reinnervation could still occur depending on the level of injury and duration of time that has passed.
• In other words, will the regenerating nerve fibers reach the motor end plate before the muscle becomes non-responsive?
• In the case of complete disruption of the motor nerve pathway, this is within one year of injury.
• If late, treat with non-reinnervation procedures (e.g., tendon transfers, fusion, free functioning muscle transfer) for the motor component, and consider nerve procedures to decrease pain or restore critical sensation.
• Chronic presentation of a nerve injury:
• Can not reinnervate what is denervated with respect to motor function except in cases (such as nerve compression) where some fibers remain in continuity.
• Otherwise, restore motor function with non-reinnervation procedures as above.
• Might be worthwhile to do nerve procedures to decrease pain or restore critical sensation.
Also see E&M Pathology-specific Management for further information.