The influence of intrinsic disc degeneration of the adjacent segments on its stress distribution after one-level lumbar fusion
The influence of intrinsic disc degeneration of the adjacent segments on its stress distribution after one-level lumbar fusion
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DOI：
10.1007/s00586-014-3462-0
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发表时间：
2015-04-01
影响因子：
2.8
通讯作者：
Yeom, Jin S.
中科院分区：
文献类型：
--
作者：
Kim, Ho-Joong;Kang, Kyoung-Tak;Yeom, Jin S.
退变的存在改变了特定退变椎间盘内的应力。因此，邻近单节段融合的节段椎间盘退变状态将影响同一相邻椎间盘随后进一步退变的速率。因此，本研究的目的是探讨生物力学的影响，在相邻节段的椎间盘退变对相应节段的应力后，一个节段腰椎融合使用验证的有限元（FE）模型。三个验证的L2-L5有限元模型，不同程度的椎间盘退变（正常，轻度，中度）在L2-L5模拟。基于代表每个级别椎间盘退变的完整模型，开发了匹配的L3-L4内固定融合模型。因此，模拟了三个完整模型和三个匹配的融合模型。在400 N的预压缩随动载荷下，在三个完整模型的L2上级终板上施加模拟屈曲、伸展、侧弯和扭转五个步骤的7.5 Nm力矩。融合模型采用混合加载方案。比较不同退变程度下融合模型与完整模型的L2-L3和L4-L5节段椎间盘内压力和纤维环最大von Mises应力的变化，椎间盘退变导致退变椎间盘处纤维环最大von Mises应力增加，与前屈、后伸、侧弯和扭转力矩下椎间盘退变有关。此外，在混合方案下，融合还增加了近端和远端相邻节段纤维环的最大von Mises应力。近端相邻节段的瓣环应力增加大于远端相邻节段。然而，融合手术对邻近节段纤维环应力增加率的贡献并不随邻近节段椎间盘退变程度的增加而增加，本研究表明椎间盘退变本身和融合可导致邻近节段椎间盘应力增加。然而，它们似乎没有协同作用。因此，正确的融合范围的决定需要综合考虑关节突退变、椎管狭窄和患者活动的程度。
The presence of degeneration alters the stress within that particular degenerated disc. Therefore, the state of degeneration of the disc at the level adjacent to a single level fusion would influence the rate of subsequent further degeneration of that same adjacent disc. Therefore, the purpose of this study was to investigate the biomechanical effect of the disc degeneration at the adjacent segment on the stress of the corresponding segment after one segment lumbar fusion using validated finite element (FE) models.Three validated L2-L5 FE models with different grades of disc degeneration (normal, mild, moderate) at the L2-L5 were simulated. Based on the intact models that represented each grade of disc degeneration, the matched L3-L4 instrumented fusion models were developed. Therefore, three intact models and three matched fusion models were simulated. Under the 400-N pre-compressive follower loading, 7.5 Nm moments simulating flexion, extension, lateral bending, and torsion in five steps were imposed on the L2 superior endplate of three intact models. The hybrid loading protocol was utilized for the fusion models. The intradiscal pressure and the maximal von Mises stress of the annulus fibrosus in the L2-L3 and L4-L5 segments were analyzed and compared between fusion and intact models with each grade of disc degeneration.Disc degeneration led to an increase of maximal von Mises stress of annulus fibrosus at this degenerated disc, related to disc degeneration under flexion, extension, lateral bending and torsion moments. Furthermore, the fusion also increased a maximal von Mises stress of annulus fibrous at both proximal and distal adjacent segments under hybrid protocol. The increases of annular stress were greater at the proximal adjacent segment than those at distal adjacent segment. However, the contribution of the fusion surgery to the increment rate of annulus fibrosus stress at the adjacent segment did not increase in relation with disc degeneration states at the adjacent segment.The present study demonstrates disc degeneration per se and fusion can cause the increase of disc stress at the adjacent segment. However, they seem not to act synergistically. Therefore, the proper decision of fusion extent needs comprehensive individual considerations about the degree of facet degeneration, canal stenosis and patient's activity.