HISTOMORPHOMETRIC CHARACTERISTICS AND PATHOGENIC MECHANISM OF PERONEAL NERVE NEUROPATHY IN EXPERIMENTAL FRACTIONAL LOWER LEG LENGTHENING

Abstract

Purpose – to study histomorphometric characteristics and pathogenic mechanism of peroneal nerve neuropathy in experimental lower leg lengthening by one millimeter per day in four increments. Methods. The authors performed lengthening of lower leg in 12 adult mongrel dogs at 14-15% of initial length by Ilizarov technique. 28 days after the leg distraction, 30 days after its fixation in the device and 30 days after the Ilizarov fixator dismounting the authors withdrew the animals from the experiment. Peroneal nerve portions were examined using light microscopy, histomorphometry of the full-color images of the giant epoxy semifine sections stained with methylene blue and diamond fuchsin. Results. Planimetric investigation demonstrated 15% decrease (p0.05) in the total area of nerve fiber bundles after distraction confirming transverse contraction of intrafascicular content. Fibrosis, increased cellularity of epineurium as well as the decrease in adipocyte number and size was observed in result of distraction and fixation. Neuropathy of the peroneal nerve was observed in one of the 12 animals – more than 80% of myelinated fibers demonstrated destructive changes, the large arteries of epineurium demonstrated obliterated lumina, part of arteries had necrobiotic changes in the cellular elements of the walls. In the remaining animals the proportion of the transformed myelinated fibers in the experiment time frame amounted to 6.0±1.4%, 4.3±1.3% and 4.2±0.4% (normally: 1.9±0.3%), no marked vascular damage was observed, the number of epineural vascular modules increased up to 6.0±1.5 (contralaterally – up to 4.0±1.6), the number of endoneural microvessels was increased at 35.5%, 10.9% and 38.9% (p0.05) in respect of intact norm (141.8±8.7 per 1 mm2). Reduced proportion of capillaries with open lumina confirmed vasomotion disorder. The changes analysis in the distribution of myelinated fibers by diameter and mean size indicates the distinct axonal atrophy, deand re-myelinaton. The mean diameter of axons and myelin thickness remained respectively 7% and 14% below normal (p0.05) in 30 days after the fixator dismounting. Conclusion. Good structural preservation of the majority of peroneal nerve fibers during leg lengthening in the manual fractural mode is ensured by integrity and hypervascularization of the nerve membranes. Axonal atrophy and hypomyelination observed in part of the fibers is associated with epineurium thinning due to decreased adipocytes content and their size. Histologically documented neuropathy was observed in one case of twelve along with lumina obliteration of main epineural arteries.