An assessment of current techniques for inducing axon regeneration and neurological recovery following peripheral nerve trauma

• Sensory nerve grafts promote axon regeneration and neurological recovery under limited conditions.
• Conduits filled with various cells, factors and other materials induce axons to regenerate about the same or somewhat longer distances than sensory nerve grafts.
• Conduits filled with platelet-rich plasma induce more axons to regenerate extensively longer distances than sensory nerve grafts and establish recovery of neurological function.
• The combination of conduits filled with platelet-rich plasma with other techniques will probably lead to even more extensive and reliable axon regeneration and development of greater neurological recovery.

Restoring neurological function to a damaged peripheral nerve separated by a gap requires axon regeneration (1) across the gap, no matter its length, and then (2) through the distal portion of the nerve, regardless of the time between the trauma and repair, and irrespective of animal or patient age. Sensory nerve grafts, the clinical “gold standard”, and most alternative techniques for bridging nerve gaps, promote reliable axon regeneration only across nerve gaps <2 cm in length, and with few axons regenerating when nerve repairs are performed >2 months post-trauma or for patients >20 years of age. Three novel nerve repair techniques are discussed that induce axon regeneration and neurological recovery clinically under conditions where other techniques are ineffective: for nerve gaps up to cm long, repairs performed as late as 3.25 years post-trauma, and for patients up to 58 years old. The mechanisms by which these techniques may work are discussed. Although these techniques provide significant improvements in the extents of axon regeneration and neurological recovery, more extensive and reliable clinical recovery of neurological function is needed and will probably require the simultaneous application of multiple techniques.