不同减压范围下行BioFlex动态稳定系统内固定对邻近节段椎间盘应力的影响

Influences of Bio Flex dynamic stabilization system fixation on the stress of adjacent segments of intervertebral disc at different decompression ranges

背景:BioFlex系统作为一种新型的经椎弓根固定的动态稳定装置,国内外对其生物力学的报道较少。目的:探讨不同减压范围行Bio Flex系统固定后对邻近节段椎间盘应力的影响。方法:选取8具新鲜牛腰段脊柱标本,应用电子万能试验机模拟人体在3种常见生理状态下(站立、坐位弯腰和站立位手提20 kg重物并弯腰)腰椎椎间盘所承受的轴向载荷(500,900,2 300 N),每具标本逐级减压建模分为5个组:1完整状态组;2完整状态+Bio Flex组;3椎板部分切除+Bio Flex组;4关节突内侧1/2切除+Bio Flex组;5关节突全部切除+Bio Flex组。应用应变片记录邻近椎间盘纤维环所受的应力,通过电子万能试验机记录的载荷-位移曲线计算刚度变化值。结果与结论:1邻近节段椎间盘的应力随着减压范围的扩大而增加,相对于完整状态,行Bio Flex固定后其应力均明显增加,差异有显著性意义(P<0.05);关节突内侧1/2切除+Bio Flex组与椎板部分切除+Bio Flex组相比,增加明显,差异有显著性意义(P<0.05);但是椎板部分切除+Bio Flex组与完整状态+Bio Flex组、关节突全部切除+Bio Flex组与关节突内侧1/2切除+Bio Flex组相比差异均无显著性意义(P>0.05);2轴向刚度随着减压范围扩大而逐步减少,但是与完整状态相比行Bio Flex固定后轴向刚度值均增加明显,4种重建结构之间两两比较差异不显著;3结果表明Bio Flex固定后随着脊柱减压范围的扩大,其邻近节段椎间盘所受的应力逐步增大,但不同减压范围不会影响其重建脊柱结构的刚度。

BACKGROUND： BioFlex system as a new pedicle screw fixation of dynamic stabilization device has less been reported concerning its biomechanics. OBJECTIVE： To study the effect of BioFlex system fixation at different decompression ranges on disc stress at adjacent segments. METHODS： Eight samples of fresh calf spines were used. Under physiologic axial loads （500, 900, 2 300 N）, electronic universal testing machine was used to simulate the lumbar spine at three physiological states （standing, sitting and bending, standing on a portable 20 kg weight and bending）. Progressive decompression modeling for each specimen and dividing into five groups： （1） complete status group; （2） complete status ＋ BioFlex group; （3） partial laminectomy ＋ BioFlex group; （4） 1/2 medial facetectomy ＋ BioFlex group; （5） total facetectomy ＋ BioFlex group. Strain gauges were used to record the stress of disc annulus. Electronic universal testing machine was used to record load-displacement curve and calculate stiffness. RESULTS AND CONCLUSION： （1） The stress of the adjacent segment of the intervertebral disc increased with the expansion of the range of decompression. Compared with the complete status, stress obviously increased after BioFlex fixation, showing significant differences （P 〈 0.05）. The stress was significantly increased in the 1/2 medial facetectomy ＋ BioFlex group compared with the partial laminectomy ＋ BioFlex group （P 〈 0.05）. However, no significant difference was detected between the partial laminectomy ＋ BioFlex group and complete status ＋ BioFlex group, and between total facetectomy ＋ BioFlex group and 1/2 medial facetectomy ＋ BioFlex group （P 〉 0.05）. （2） Axial stiffness reduced with the expansion of the range of decompression. Compared with the complete status, axial stiffness noticeably increased after BioFlex fixation. The difference was not significant among four kinds of reconstruction structures. （3） These findings confirmed that after BioFlex fixation, with the expansion of the range of decompression, the stress of adjacent segments of intervertebral disc gradually increased, but different ranges of decompression cannot affect the stiffness of reconstruction structure. Subject headings： Internal Fixators; Decompression, Surgical; Intervertebral Disk; Biomechanics; Tissue Engineering