Structural reorganization of the sciatic, peroneal, and tibial nerves during osteosynthesis of lower leg fracture and after fracture consolidation (an experimental study)

Abstract

The study purpose was to identify histological changes in the peripheral nerves and determine functional significance of subclinical neuropathy in experimental simulation of lower leg fractures. We simulated a tibial shaft fracture in 24 dogs under anesthesia and performed osteosynthesis using an Ilizarov apparatus. After 7, 14, 20, 35–37, and 50 days of fixation using the apparatus and 30, 60–90, and 120 days after removal of the apparatus, the dogs were euthanised. Electromyography was performed before fracture and within the main phases of the experiment. Samples of the sciatic, peroneal, and tibial nerves were studied histologically using computer morphometry of semithin araldite sections. After 37 days of fixation, the amplitude of M-responses of the tibialis anterior and gastrocnemius muscles decreased by 70% compared to the baseline value, increased after removal of the apparatus, but not restored. There were no sighs of nerve damage by bone fragments or wires. The fraction of degenerating myelinated fibers in the studied nerves was less than 13%. Reorganization of the Remak bundles led to a temporary increase in the number density of nerve fibers. Along with axonal atrophy, the peroneal nerve was characterized by demyelination-remyelination, and the tibial nerve was characterized by hypermyelination. The dynamics of numerical density of endoneurial blood vessels was also different. Despite minor sharp degenerative changes in myelinated fibers, persistent axonal atrophy, demyelination, and retrograde changes were not compensated for up to 120 days after removal of the apparatus. Correlations between the morphometric parameters of myelinated fibers and the M-response amplitude indicated a causal role of subclinical neurological changes in functional outcomes of fractures.