Evaluation of long-term results of single intraoperative electrical neurostimulation after autologous plastic surgery of a resection defect of the tibial portion of the sciatic nerve in adult rats

Introduction World literature data indicate the effectiveness of single intraoperative electrical stimulation (IES) of the proximal segment of the damaged nerve to stimulate its regeneration, but there is no data on its effect on the long-term results of autoplasty of resection defects.

The purpose of the work was to evaluate the long-term results of a single IES after autologous plastic surgery of the tibial portion of the sciatic nerve in rats.

Materials and methods Thirty rats after autologous repair of the resection defect of the tibial portion of the sciatic nerve were divided into series 1 (unstimulated control, n = 16) and series 2 (single IES for 40 minutes, n = 14). At 4 and 6 months after surgery, the static sciatic functional index (SFI) and morphometry of epoxy transverse semithin sections of the tibial nerve at the level of the middle third of the leg were assessed. For comparison with the normal values, the corresponding data from 7 intact rats were used.

Results The number of animals with excellent results of SFI restoration was 12.5 % in  series 1 and  50 % in  series  2 (p = 0.05). The numerical density of regenerated myelinated fibers (MF) exceeded the norm: in series 1 — by 63 % (p < 0.01) and 34 % (p < 0.01), in series 2 — by 58 % (p < 0.01) and 47 % (p < 0.01), respectively. In series 2, there were greater values in comparison with series 1: the median diameters of MFs were by 11.7 % and 15.7 %, the median diameters of their axons were by 5.4 % and 11.9 %, the median thickness of the myelin sheath was by 17.0 % and 24.1 %, respectively (p < 0.05 4 months and p < 0.01 6 months after surgery). Four months after surgery in series 1 and 2, the numerical densities of endoneurial vessels exceeded the intact control by 134 % (p < 0.05) and 156 % ( 0.05), their average diameters by 18 % and 16 % (p < 0.01) respectively, and lumen diameters increased only in series 2 by 8 % (p = 0.07). After 6 months of the experiment in series 1 and  2, the  numerical densities of microvessels decreased, but significantly exceeded the control by  66 % (p < 0.05) and 83 % (p < 0.05), the average diameters — by 14 % and 36 % (p < 0.05), lumen diameters — by 26 % (p < 0.05) and 50 % (p < 0.01), respectively.

Discussion The difference between stimulated and unstimulated animals in all MF size parameters 6 months after surgery was greater than after 4 months, indicating a persistent neuroregenerative effect.

Conclusions A significant increase in the diameters of regenerating nerve fibers in the tibial nerve, as well as the diameters of their axons and the thickness of the myelinated sheaths 4 and 6 months after autoplasty of the tibial portion of the sciatic nerve in the group of animals with a single 40-minute IES of the proximal portion of the sciatic nerve indicates the promoting effect of the applied additive effect on regenerative axono- and myelinogenesis. Increase in the lumens and improvement of blood flow of the endoneurial vessels of the tibial nerve in the series with IES ensured the stability of the neuroregenerative effect. The functional significance of the effects of a single IES is confirmed by a significantly higher percentage of animals with excellent results in restoring the static functional index.

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