Morphology and morphometry of peripheral nerves after spinal cord injury

The morphology of peripheral nerves sampled at the time of nerve transfer surgery was directly assessed in 13 participants (mean age at injury 27±8 years and motor level of C4 or below) within 15 months of their spinal cord injury (SCI). Donor nerves included teres minor (TM), posterior axillary (PAX), brachialis (BRAC), extensor carpi radialis brevis (ECRB) and supinator (SUP) nerves. Recipient nerves included those to triceps (TRI), posterior interosseus (PIN) and anterior interosseus (AIN). Fresh nerve samples were fixed in glutaraldehyde, processed and embedded in Araldite Epon. Multiple semi-thin sections from each nerve sample were cut, mounted onto slides, stained with methylene blue or toluidine blue, and imaged by light microscopy using an Olympus BX60 microscope. Glutaraldehyde-fixed nerve specimens were post-fixed with osmium tetroxide, stained with uranyl acetate and alkaline lead citrate and embedded in Epon/araldite. Ultrathin sections were cut and examined using a JEOL 1400 Series transmission electron microscope. Qualitative data were recorded from the nerve specimens according to various morphologic criteria. A comprehensive quantitative morphometric analysis of axon, fibre and myelin areas and diameters and g-ratios was also undertaken.
Over two-thirds of both donor and recipient nerves showed abnormalities that differed in appearance and aetiology. These included myelin thickening and folding (tomacula), demyelination, reduced density of large, myelinated axons, oedematous endoneurium, evidence of compression, and thickened epineurium and perineurium. Morphometric analysis showed differences in axon density and myelination in the sampled nerves, with significant nerve fibre loss in teres minor and posterior axillary nerves, and increased myelin area in the other nerves. The g-ratio was significantly reduced by the degree of myelin thickening. The morphological findings show evidence of widespread peripheral nerve pathology after spinal cord injury.

本研究对13名脊髓损伤（spinal cord injury, SCI）后15个月内的受试者（受伤时平均年龄27±8岁，运动损伤平面为C4及以下）在神经转位手术中采集的外周神经形态进行直接评估。供体神经包括小圆肌（teres minor, TM）神经、腋后（posterior axillary, PAX）神经、肱肌（brachialis, BRAC）神经、桡侧腕短伸肌（extensor carpi radialis brevis, ECRB）神经与旋后肌（supinator, SUP）神经；受体神经包括肱三头肌（triceps, TRI）神经、骨间后（posterior interosseus, PIN）神经与骨间前（anterior interosseus, AIN）神经。
将新鲜神经标本经戊二醛（glutaraldehyde）固定后，进行梯度脱水并包埋于Araldite Epon环氧树脂中。从每份神经标本切取多张半薄切片，贴片于载玻片后以亚甲蓝或甲苯胺蓝（toluidine blue）染色，采用奥林巴斯BX60（Olympus BX60）光学显微镜进行成像。
经戊二醛固定的神经标本经四氧化锇（osmium tetroxide）后固定，以醋酸铀（uranyl acetate）与碱性柠檬酸铅（alkaline lead citrate）双重染色后包埋于Epon/Araldite混合树脂中。切取超薄切片后，使用JEOL 1400系列透射电子显微镜进行超微结构观察。根据多项形态学评判标准对神经标本进行定性数据记录，并针对轴突、神经纤维及髓鞘的面积、直径与g-ratio开展了全面的定量形态计量分析。

超过三分之二的供体与受体神经均出现形态与病因各异的异常改变，包括髓鞘增厚与折叠（tomacula）、脱髓鞘、大直径有髓轴突密度降低、神经内膜水肿、压迫征象，以及神经外膜与神经束膜增厚。形态计量分析结果显示，采集的神经标本在轴突密度与髓鞘化程度上存在差异：小圆肌神经与腋后神经出现显著的神经纤维丢失，其余受试神经的髓鞘面积则有所增加；髓鞘增厚程度可显著降低g-ratio。本研究的形态学结果证实，脊髓损伤后存在广泛的外周神经病理改变。