Phillips, J. B. and Mason, S.
An ultrastructural and histological investigation of structural features related to biomechanical properties of human peripheral nerves at joint and non joint regions.
In: 2011 PNS Biennial Meeting of the Peripheral Nerve Society, 25-29 June 2011, Potomac, Maryland, US.
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Peripheral nerves need to bend and stretch around joints in the limbs during normal movement. If this ability is compromised due to injury or disease then localised tension can result in damage and loss of function. Understanding how nerves function in biomechanical terms is an important research topic and translating observations made in animal models to the clinical situation is a critical step. Rat nerves exhibit localised strain differences and are more compliant at regions where they traverse joints. A corresponding regional heterogeneity in collagen fibril diameter has been observed in the rat median nerve, with fibrils at the joint region being thinner and more numerous than those in non joint regions. Earlier studies in humans suggested that an increase in fascicular number may help nerves resist the forces present at joints. To examine further whether increased fasciculation and/or variation in collagen fibril diameter occurs in human peripheral nerves where they traverse the elbow and wrist joints, a comparative ultrastructural and histological examination of cadaveric median, ulnar and radial nerves was undertaken. Two joint regions (elbow and wrist) and one non joint region (mid-forearm) were studied in each nerve. Collagen fibrils in the endoneurium, perineurium and epineurium were measured using transmission electron microscopy, and fascicle numbers were analysed by light microscopy. In the median nerve there was a similar trend in collagen fibril diameter to that seen in the rat, with thinner fibrils at the joint regions compared to the non joint region. The ulnar and radial nerves did not show this trend. Additionally, the median and ulnar nerves showed an increased number of fascicles at the wrist compared to the other areas studied. The biomechanical properties of human nerves have not been fully characterised and the extent to which stiffness varies along their length has not been measured directly. It is interesting therefore that the human median nerve shows the same pattern of joint-related ultrastructural characteristics as the rat nerve, suggesting that localised collagen fibril diameter may be a key feature contributing to median nerve mechanical architecture.
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