The type of pathology vastly changes the appropriate management choice.
The six degrees of nerve injury can help organize the various types of pathology and subsequent associated management strategies.
Six Degrees: for further details refer to the anatomy and physiology section.
Summary of the six degrees in the case of timely (early) presentation:
1st-4th degree injuries occur in conjunction with closed (more common) or open (less common) mechanisms of injury.
• 1st and 2nd degree injuries:
• Examples: 1st degree--ischemia or demyelination due to nerve compression, 2nd degree--axonotmesis with nerve fiber Wallerian degeneration but full regeneration down the appropriate path will occur.
• Will likely recover better with minimal surgical intervention (decompression of the recovering nerve at known sites of compression can be helpful).
• Do NOT cut out a 1st through 2nd degree injury in an attempt to make it better.
• 3rd degree injuries:
• Example: same as second degree but with scarring within the nerve that might prevent some function from returning.
• Depending on the extent of scarring a 3rd degree injury may be better with or without surgery--be careful with these and observe closely in the early period post-injury, if the critical component of that nerve function is scarred, then surgical treatment (in addition to decompression) may be indicated.
• Usually, however, a 3rd degree injury offers potential for better recovery then a surgical graft repair unless it is very painful--then excision and graft may be indicated for pain relief.
• 4th degree injuries
• Examples: Motorcycle accident traction or crush injury that are closed but have high energy and lead to complete scarring of the nerve, gunshot wound that doesn’t actually penetrate nerve directly (which would be a 5th degree injury) but due to the associated blast effect produces complete scarring of the nerve.
• Will not get better without surgery because scar completely blocks the regenerating nerve.
• Several management strategies are appropriate such as:
• Scar resection and direct nerve repair or interposition graft
• Distal nerve transfer procedures.
4th, 5th and sometimes 6th degree injuries benefit from surgical intervention
• 4th degree injuries--see above.
• 5th degree only occurs with an open injury and is a nerve transection injury:
• Emergent (at-time-of-injury) management is indicated for patients with concomitant injuries that would preclude later reexploration (median nerve transection with an associated brachial artery laceration requires urgent repair for the arterial injury--if possible, nerve repair with significant trimming to ensure that you are out of the zone of injury can be done) or would benefit from mapping of the distal branches while neurotransmitter in the distal stump allows.
• Subacute management of a 5th degree injury is also reasonable (when the surgeon is rested and appropriate equipment and ancillary staff are available)--if there is concern over injuring a recent vascular repair, an extraanatomic graft or more distal nerve transfer procedures can be done; otherwise traditional exploration and direct repair after judicious trimming is acceptable.
• 6th is a combination of some intact/normal nerve fibers along with some or several of the 1st through 5th degree injury patterns:
• It may or may not benefit from some type of intervention.
• For example, a 6th degree proximal median nerve injury with no pain, intact distal motor function and loss of sensation would be best treated with distal sensory nerve transfer from the fourth to first web space. This avoids disruption of the intact motor fibers that might occur with direct exploration and grafting of the neuroma-in-continuity.
(((Also link to the specific Surgical Options pages for further details.)))
In late presentation or for very proximal injuries where the nerve fibers will not reach the motor end plate in time (generally this is one year from time of injury) for reinnervation to occur the following is recommended:
• Do NOT excise the injured nerve segment and do direct or interposition nerve graft to restore motor function--this will not work
• Do NOT do a distal nerve transfer to reinnervate the non-functional muscle--this will not work
• Consider nerve repair/interposition grafting to the non-functional sensory territory as sensation is not time dependent and (often) protective sensation can be restored even years after injury.
• Consider tendon transfers, fusions, free muscle transfers or other adjunct procedures for motor function restoration.
• Please note that this is only true for injuries in which there are no motor fibers in contact with the muscle end-organ that are keeping it available for reinnervation. Injuries such as 1st, 2nd, 3rd and some 6th degree injury types that do have motor fibers in continuity may still benefit from further strategies to allow for additional motor fibers to be directed to the motor end organ to improve function such as nerve decompression, etc.