Histomorphometric assessment of the tibial nerve and small muscles of the foot after internal neurolysis and autogenous plastic surgery of the tibial portion of the sciatic nerve in rats

Introduction Transformations of the nerves and muscles of the distal extremities after nerve injuries at the level of the proximal segments are critical for the restoration of functions, but have not been sufficiently studied in experimental biological models. Purpose Histomorphometric evaluation of the tibial nerves and plantar interosseous muscles after internal neurolysis and autogenous plasty of the tibial portion of the sciatic nerve (SN) in rats. Materials and methods The study was performed on 21 male Wistar rats, aged 8-10 months. Series 1 (internal SN neurolysis) – n = 6. Series 2 (autogenous SN neuroplasty) – n = 8. Control – 7 intact rats. The rats were euthanized 6 months after the operation. Light microscopy and histomorphometry of transverse semithin sections of the tibial nerve at the level of the middle third of the lower leg and paraffin sections of the plantar interosseous muscles of the foot were performed. Results In series 1, endoneural vessels had increased diameters and wall thickness in the tibial nerve, but a smaller lumen compared to the norm; the dimensional characteristics of the myelinated fiber population were increased due to myelin decompactization and axonal edema; about 10 % of myelinated fibers were destructively changed. In series 2, the numerical density of the endoneural vessels of the tibial nerve was doubled in comparison with the intact one; the numerical and dimensional composition of the regenerated myelinated fibers indicated active but incomplete regeneration. The vascularization index of the plantar interosseous muscles in series 1 was close to normal, in series 2 it decreased twice, the median of muscle fiber diameters was reduced by 12.41 % (p = 0.000) and 20.96 % (p = 0.000), respectively. Muscle fibers with a diameter of more than 30 μm increased in series 2 compared to series 1. Conclusion Internal neurolysis and interfascicular autoplasty of the sciatic nerve cause multidirectional changes in the endoneural vessels of the tibial nerve, which predetermine the multidirectional nature and severity of denervation and reinnervation changes in the nerves of the lower leg and small muscles of the foot.