The origin of regenerating axons after end-to-side neurorrhaphy without donor nerve injury.

The purpose of this study was to determine the origins of regenerated axons after end-to-side neurorrhaphy (ETSN) without donor nerve injury by comparing the time of appearance of regenerating axons for proximally coapted ETSN and distally coapted ETSN. Thirty rabbits were used in each group. In the proximal ETSN group, the ulnar nerve was transected and the distal end sutured to the median nerve 3cm above the elbow joint, whereas in the distal ETSN group, it was 3cm below the elbow joint. Coaptation was performed by wrapping the aponeurosis of nearby muscle. Observations were made weekly for 6 weeks after ETSN. Axonal regeneration was studied by morphometric analysis and immunohistochemistry. The times of appearance of regenerating axons differed in the proximal and distal ETSN groups. Axonal densities in proximal segments of donor nerves continuously increased and the axonal diameters of proximal segments of donor nerves continuously decreased with time after ETSN. Our findings suggest that regenerated axons after ETSN without donor nerve injury originate from the central nervous system rather than coaptation sites.