EUROMEDICA  Hanover 23-24  Mai 2011	Advanced methods of diagnosis, treatment and prophylactics
	European Academy of Natural Sciences, Hanover European Scientific Society, Hanover

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Biomechanics of the peripheral nervous system is one of the pressing problems of functional neuromorphology whose solution has practical importance in connection with the prevalence and severity of medical and social consequences of damage to the nerve trunks. The least studied in the biomechanical reliability of nerves is the question of the sequence included in the process of deformation of structural elements in the transition of small deformations in the large. In this regard, the aim of our study was to examine the influence of the structural elements of the nerve trunks of varying degrees of tension.

Material studies provided the median and ulnar nerves of 78 corpses of adults 21-60 years of both sexes. Strength-strain properties of nerves have been studied by tensile testing machine, change the architectonics of the constituent elements under strain - in histological preparations stained with hematoxylin-eosin, picrofuchsin and impregnated with silver nitrate on the Gros-Bilshovsky-Campos.

The study showed that under tension to 5-7% of the initial length of the elongation of the nerve occurs, firstly, by straightening the folding of nerve bundles, nerve fibers and connective tissue membranes and, secondly, stretching the elastic fibers. At this stage, a relatively small deforming load causes a significant lengthening of it. Subsequent deformation to 10-13% of the original length of the nerve requires a substantial increase in workload. In this case, it is observed stretching of connective tissue membranes lost waviness of collagen fibers. Adaptation of the nerve fibers to increase the length of the nerve occurs at the expense of smoothing their undulations are a small residual pool of a strain. At this stage the dependence of the “load-strain” is nonlinear and does not obey Hooke’s law.

Thus, under small strain stretching of the nerve occurs at the expense of connective tissue, and mainly elastic fibers. Structures that determine the strength and elasticity of the nerves at small strains, are their connective tissue sheath and epineurium in the first place. The thickness of the epineurium and the total area of connective tissue in the cross-section of the nerve is most closely correlated with its biomechanical properties at this stage of deformation.

In the second phase of deformation is stretching as collagen and elastic, so as nerve fibers. For small strains, the collagen does not significantly affect the strength properties, but clearly defines them in case of overload. At the stage of large strains over 20-22% protective role of biomechanical epineurium is exhausted and its connective tissue fibers with increasing strain are destroyed. The main factors of anti-elongation at this stage are the nerve fibers and perineurium. By 25-30%th threshold stretch nerve fibers pass into the phase of plastic deformation and start to disintegrate. Nerve trunk retains its external anatomical integrity by perineurium. High strength is determined perineurium laminated, large thickness of layers and different orientation of the connective tissue fibers.

Thus, the structural foundations of biomechanics of nerves at the stage of small and large strains are different. When they stretched up to break a gradual transition of security functions from one set of structural components to the other. At the initial stage of shock-distorting load is the epineurium, and the stage of large deformations close to the break - perineurium. Furthermore, it should be borne in mind that stretching of the nerve causes a narrowing of its perineural sheath, naturally leading to a rise intratruncal pressure, compression of nerve fibers and intratruncal blood vessels and, consequently, conduction abnormalities before the appearance of macroscopically visible changes.