"Donor" muscle structure and function after end-to-side neurorrhaphy

End-to-end nerve coaptation is the preferred surgical technique for periphe ral nerve reconstruction after injury or tumor extirpation. However, if the proximal nerve stump is not available for primary repair, then end-to-side neurorrhaphy may be a reasonable alternative. Numerous studies have demons trated the effectiveness of this technique for muscle reinnervation. Howeve r, very little information is available regarding the potential adverse seq uelae of end-to-side neurorrhaphy on the innervation and function of muscle s, innervated by the "donor" nerve. End-to-side neurorrhaphy is hypothesize d to (1) acutely produce partial donor muscle denervation and (2) chronical ly produce no structural or functional deficits in muscles innervated by th e donor nerve. Adult Lewis rats were allocated to one of two studies to det ermine the acute (2 weeks) and chronic (6 months) effects of end-to-side ne urorrhaphy on donor muscle structure and function. In the acute study anima ls underwent either sham exposure of the peroneal nerve (n = 13) or end-to- side neurorrhaphy between the end of the tibial nerve and the side of the p eroneal nerve (n = 7). After a 2-week recovery period, isometric force (F-o ) was measured, and specific force (sF(o)) was calculated for the extensor digitorum longus muscle ("donor" muscle) for each animal. Immunohistochemic al staining for neural cell adhesion molecule (NCAM) was performed to ident ify populations of denervated muscle fibers. In the chronic study, animals underwent either end-to-side neurorrhaphy between the end of the peroneal n erve and the side of the tibial nerve (n = 6) or sham exposure of the tibia l nerve with performance of a peroneal nerve end-to-end nerve coaptation (n = 6), to match the period of anterior compartment muscle denervation in th e end-to-side neurorrhaphy group. After a 6-month recovery period, contract ile properties of the medial gastrocnemius muscle ("donor" muscle) were mea sured. Acutely, a fivefold increase in the percentage of denervated muscle fibers (1 +/- 0.7 percent to 5.4 +/- 2.7 percent) was identified in the don or muscles of the animals with end-to-side neurorrhaphy (p < 0.001). Howeve r, no skeletal muscle force deficits were identified in these donor muscles . Chronically, the contractile properties of the medial gastrocnemius muscl es were identical in the sham and end-to-side neurorrhaphy groups. These da ta support our two hypotheses that end-to-side neurorrhaphy causes acute do nor muscle denervation, suggesting that there is physical disruption of axo ns at the time of nerve coaptation. However, end-to-side neurorrhaphy does not affect the long-term structure of function of muscles innervated by the donor nerve.