Peripheral nerves in the rat exhibit localized heterogeneity of tensile properties during limb movement

Abstract

Peripheral nerves in the limbs stretch to accommodate changes in length during normal movement. The aim of this study was to determine how stretch is distributed along the nerve relative to local variations in mechanical properties. Deformation (strain) in joint and nonjoint regions of rat median and sciatic nerves was measured in situ during limb movement using optical image analysis. In each nerve the strain was significantly greater in the joint rather than the non-joint regions (2-fold in the median nerve, 5-to 10-fold in the sciatic). In addition, this difference in strain was conserved in the median nerve ex vivo, demonstrating an in-built longitudinal heterogeneity of mechanical properties. Tensile testing of isolated samples of joint and non-joint regions of both nerves showed that joint regions were less stiff (more compliant) than their non-joint counterparts with joint : non-joint stiffness ratios of 0.5 ± 0.07 in the median nerve, and 0.8 ± 0.02 in the sciatic. However, no structural differences identified at the light microscope level in fascicular/non-fascicular tissue architecture between these two nerve regions could explain the observed tensile heterogeneity. This identification of localized functional heterogeneity in tensile properties is particularly important in understanding normal dynamic nerve physiology, provides clues to why peripheral nerve repair outcomes are variable, and suggests potential novel therapeutic targets.

Stretch-induced nerve conduction deficits in guinea pig ex vivo nerve

“…We surmise the differing strain zones to be partly caused by heterogeneity in the mechanical properties along the nerve. It was previously observed with rat sciatic nerve that joint regions encountered strains 5-10 times higher than non-joint sections (Phillips et al, 2004). Further histological data did not ascribe these discrepancies to degree of fasciculation.…”

Variations in the course and microanatomical study of the lateral femoral cutaneous nerve and its clinical importance

“…The factors protecting the peripheral nerves against stretching can be attributed to their anatomical structure and biomechanical characteristics (Barkmeier and Luschei, 2000;Phillips et al, 2004;Topp and Boyd, 2006;Vivo et al, 2004). The structural organization of peripheral nerves enables them to function while resisting and adapting to stresses placed on them by varying postures and movements.…”

Mechanical fatigue resistance of an implantable branched lead system for a distributed set of longitudinal intrafascicular electrodes

“…One of the potential drawbacks of targeting the nerves in the periphery is that they slide and stretch while performing routine activities [1, 26–29]. This movement presents challenges to the stability of the electrode-nerve interface and the mechanical fatigue resistance of the leads, especially in systems where the electronics are housed at a distance from the electrode-nerve interface.…”