Role of the target in end-to-side neurorrhaphy: Reinnervation of a single muscle vs. multiple muscles

The authors examined the effects of end-to-side neurorrhaphy for reinnervat ion of the musculocutaneous nerve (Group A) which innervates the biceps mus cle, compared to reinnervation of the median nerve which innervates multipl e muscles in a rat model. Additionally end-to-end neurorrhaphy to the muscu locutaneous nerve using one-third of the median nerve (Group B) was investi gated. End-to-end coaptation of the musculocutaneous nerve served as a cont rol (Group C). In a grooming test, the biceps muscle function in Group A animals demonstra ted a slower but nearly similar good recovery to Groups B and C. Biceps mus cle contraction force investigated after 24 weeks demonstrated no statistic ally significant differences among all groups. in Groups A and B, no signif icant impairment of the donor median nerve function was found in a grasping test and the muscle contraction force of the flexor carpi radialis muscle, and histologic evaluation of the musculocutaneous nerve showed multiple re generated axons distal to the coaptation site. Retrograde double-labeling i n Group A animals showed reinnervation of the musculocutaneous nerve by med ian nerve axons located at the coaptation site. These results validate that end-to-side neurorrhaphy to a nerve innervating a single muscle is more efficient than to a nerve innervating multiple mus cles, as demonstrated in an earlier study. The reason for this phenomenon i s most likely that all sprouting axons are directed toward one target rathe r than toward multiple targets, with the latter situation resulting in a sm aller number of axons and a variable distribution of axons per target. Sinc e donor nerve sprouting axons were observed at the coaptation site, a relev ance of the selected site for end-to-side neurorrhaphy is suggested. Both e nd-to-side neurorrhaphy and end-to-end neurorrhaphy, using one-third of the median nerve, led to useful functional recovery in this rat model, if an a gonistic donor nerve is employed.