Decoupled epineurial and axonal deformation in mouse median and ulnar nerves

Abstract

Introduction Peripheral nerves accommodate mechanical loads during joint movement. Hypothesized protective features include increased nerve compliance near joints and axonal undulation. How axons perceive nerve deformation is poorly understood. We tested whether nerves increase local axonal undulation in regions of high epineurial strain to protect nerve fibers from strain‐induced damage. Methods Regional epineurial strain was measured near the elbow in median and ulnar nerves of mice expressing axonal fluorescence before and after decompression. Regional axonal tortuosity was quantified under confocal microscopy. Results Nerves showed higher epineurial strain just distal to the medial epicondyle; these differences were eliminated after decompression. Axonal tortuosity also varied regionally; however, unlike in the epineurium, it was greater in proximal regions. Discussion In this study we have proposed a neuromechanical model whereby axons can unravel along their entire length due to looser mechanical coupling to the peri/epineurium. Our findings have major implications for understanding nerve biomechanics and dysfunction. Muscle Nerve 59:619–619, 2019

Spatial variation in mechanical properties along the sciatic and tibial nerves: An ultrasound shear wave elastography study

“…First, the epineurium was excluded from the ROI used to quantify the shear wave velocity. Nevertheless, a recent nerve model suggests a tightly coupled meso-epi-perineurium interacting with a loosely coupled peri-endoneurium (Sung et al, 2019). Therefore, the meso-epineurium connections have the potential to modulate the shear wave velocity of the perineurium, and consequently contribute to the spatial variations observed along the course of the nerve tract.…”

Chronic effects of muscle and nerve-directed stretching on tissue mechanics

“…Consistent with such findings and in line with our results, in a nerve repair experiment Bora et al (9) showed that although there was an initial increase in nerve tension immediately after excising a segment, the nerve returned to its uncut state of tension after seven weeks, with increased compliance within neural connective tissue observed. Additionally, the stiffness adaptations may also be related to changes in neural collagen fibril type and density (39) and in the meso᎑ epi᎑perineurium connections (55). However, such evidence is either indirect or based on studies with animals, whose growth and adaptation patterns differ from humans.…”

Neurodynamics: is tension contentious?

“…In addition, mechanical properties of peripheral nerves are not equal along their length [ 24 ], revealing a complex tissue ultrastructure [ 25 ]. A recent model of nerve layer connections has been proposed to explain the complex (whole) nerve response to stretch [ 26 ]. This model suggests that the mesoneurium, epineurium, and perineurium are coupled via viscoelastic physical connections and interact with a loosely coupled perineurium and endoneurium, allowing axons to glide and unravel throughout the length of the nerve.…”

“…This model suggests that the mesoneurium, epineurium, and perineurium are coupled via viscoelastic physical connections and interact with a loosely coupled perineurium and endoneurium, allowing axons to glide and unravel throughout the length of the nerve. Collectively, these mechanical features allow nerves to straighten without bearing significant stresses while maintaining functional and structural integrity of the delicate axons within [ 26 ].…”