Hussain Mozammil, Natarajan Raghu N, Chaudhary Gulafsha, An Howard S, Andersson Gunnar B J
Division of Research, Logan University, Chesterfield, MO 63017, USA.
J Spinal Disord Tech. 2012 Jun;25(4):218-25. doi: 10.1097/BSD.0b013e3182159776.
Biomechanics of normal vertebral segments adjacent to a degenerated segment in the cervical spine.
To test the hypothesis that posterior facet joints of adjacent segments are loaded more when degeneration occurs in the intermediate disc segment.
Degeneration progression in adjacent segments is a clinical concern. Literature studies that have documented the effects of a degenerated segment on the adjacent-segment discs have not addressed these effects on adjacent-segment posterior facets. Moreover, these biomechanical studies are performed mainly on the lumbar spine or the tissue quality of the cadavers is poor because of degenerated segments. Retrospectively, it is difficult to decipher to what extent degeneration in a single disc induces biomechanical changes in facet joints along the posterior spinal column. To date, no cervical spine biomechanical study investigated the facet joints response of adjacent segments when the disc in between those segments degenerates.
An earlier validated poroelastic, 3-dimensional finite element model of a normal C3-T1 segment was used. Two stages of degeneration (moderate and severe) were simulated in the C5-C6 disc. Disc geometry and tissue material properties were modified to simulate C5-C6 disc degeneration. For the 3 C3-T1 models, loads on the posterior facets at 3 levels (C4-C5, C5-C6, and C6-C7) were computed under moment loads.
With progressive degeneration in the C5-C6 disc, posterior facet loading in adjacent segments and in the intermediate degenerated disc segment increased. Changes in facet loading in the inferior C6-C7 segment were greater than the corresponding changes in the superior C4-C5 segment. These changes were highest in lateral bending and lowest in axial rotation.
Higher changes in facet loads along the posterior spinal column may contribute to altered biomechanics in neighboring segments. Future biomechanical experiments are required to develop a more clear understanding of the posterior facet joints response in neighboring segments because of degeneration in a cervical disc.
颈椎退变节段相邻正常椎体节段的生物力学。
验证以下假设：当中间椎间盘节段发生退变时，相邻节段的后关节突关节承受的负荷会增加。
相邻节段的退变进展是一个临床关注点。已有文献研究记录了退变节段对相邻节段椎间盘的影响，但未涉及对相邻节段后关节突的影响。此外，这些生物力学研究主要在腰椎进行，或者由于节段退变，尸体的组织质量较差。回顾性地看，很难解读单个椎间盘退变在多大程度上会引起沿脊柱后柱的关节突关节生物力学变化。迄今为止，尚无颈椎生物力学研究调查当相邻节段之间的椎间盘退变时，相邻节段的关节突关节反应。
使用先前验证过的正常C3 - T1节段的多孔弹性三维有限元模型。在C5 - C6椎间盘模拟两个退变阶段（中度和重度）。修改椎间盘的几何形状和组织材料特性以模拟C5 - C6椎间盘退变。对于3个C3 - T1模型，在弯矩载荷下计算3个水平（C4 - C5、C5 - C6和C6 - C7）后关节突的负荷。
随着C5 - C6椎间盘的渐进性退变，相邻节段以及中间退变椎间盘节段的后关节突负荷增加。C6 - C7节段下方关节突负荷的变化大于C4 - C5节段上方相应的变化。这些变化在侧弯时最高，在轴向旋转时最低。
沿脊柱后柱的关节突负荷的较大变化可能导致相邻节段生物力学改变。由于颈椎间盘退变，需要未来的生物力学实验来更清楚地了解相邻节段后关节突关节的反应。
