Reinnervation of denervated muscle in a split-nerve transfer model

This study was performed to quantify the reinnervation of denervated muscle in a split-nerve transfer model and to determine any possible downgrading effects on the donor nerve and its end organ. Fifty-four adult Wistar rats weighing 200 to 250 g were used. The experimental design consisted of two groups. The motor nerve branch to the anterior tibial muscle and gastrocnemius muscle of the right hind limb were dissected in all rats. In the experimental group (N = 36), the motor nerve branch of the tibial nerve to the gastrocnemius muscle was exposed, cut, and ligated. The motor nerve branch to the anterior tibial muscle was split and transected longitudinally, and the medial half was routed posteriorly. End-to-end neural anastomosis was performed between this medial half of the split nerve and the distal stump of the gastrocnemius nerve. In the control group (N = 18), while the same surgical preparation was performed, the motor nerve branch to the anterior tibial muscle and gastrocnemius nerve were exposed and transected, and the nerve endings were ligated, but neural anastomosis was not performed between these nerves. The left hind limb of all rats served as a normal comparison side without any surgical intervention. Both of the groups were divided into three subgroups (12 rats each for the experimental groups and 6 rats each for the control group) to evaluate the results after periods of 1, 3, and 6 months. Electromyography, light microscopic and morphometric examination, and muscle weight measurements were used to document the results. Although stimulation of the peroneal and tibial nerves did not produce any compound muscle action potential (CMAP) recordings from either the anterior tibial or the gastrocnemius muscle in the control group, the normalized CMAP areas of the tibial nerve were (mean +/- standard deviation) 16.2 +/- 30.8% in the 1-month group, 63.4 +/- 34.7% in the 3-month group, and 72.4 +/- 16.3% in the 6-month group. For the peroneal nerve, the normalized CMAP areas were 17.0 +/- 32.2%, 53.4 +/- 29.4%, and 54.4 +/- 14.5% for the 1-, 3-, and 6-month groups in the experimental groups respectively. A high number of regenerating myelinated nerve fibers was identified in the distal part of the coapted motor nerve branch to the gastrocnemius muscle. The average number of myelinated fibers in the lateral half of the split nerve in the experimental group was 15,108 fibers per square millimeter, 14,167 fibers per square millimeter, and 19,830 fibers per square millimeter at months 1, 3, and 6 respectively. The average number of fibers proximal to the nerve anastomotic site was 15,423 fibers per square millimeter, 19,200 fibers per square millimeter, and 20,774 fibers per square millimeter. Distal to the nerve anastomotic site, the number of myelinated fibers was 17,941 fibers per square millimeter, 18,885 fibers per square millimeter, and 18,895 fibers per square millimeter at 1, 3, and 6 months respectively. There were no myelinated fibers in the control group sections. There were significant differences in muscle weight between the experimental and control groups at the end of month 6. The difference between the experimental side and the untouched normal healthy side was not significant in the weight measurements of both muscles. The results show acceptable reinnervation by split-nerve transfer with minimal functional impairment of the donor muscle. This study confirms that split-nerve transfer is a reliable method of reconstruction for paralyzed muscle with minimal donor area morbidity.