Department of Neurosurgery, Inje University College of Medicine, Seoul Paik Hospital, Seoul, Korea.
Eur Spine J. 2013 May;22(5):1066-77. doi: 10.1007/s00586-012-2611-6. Epub 2012 Dec 16.
PURPOSE: The aims of the present study were to compare the biomechanical effects on the adjacent segments after mono-segmental floating fusion with posterior semi-rigid or rigid stabilization, and to evaluate the effect of the amount of fusion mass on the biomechanical differences. METHODS: A detailed, nonlinear L1-S1 finite element model had been developed and validated. Then five models were reconstructed by different fixation techniques on the L3-L4 level: rigid fixation with an interbody spacer (Ti + IS), rigid fixation with a large interbody spacer (Ti + IS_all), semi-rigid fixation with an interbody spacer (PEEK + IS), semi-rigid fixation with a large interbody spacer (PEEK + IS_all), and semi-rigid fixation only (PEEK). Analyses were conducted for the case of erect standing position, flexion, and extension motion. RESULTS: At L1-L2 and L2-L3, PEEK + IS demonstrated less inter-segmental rotation and nucleus pressure increments from the intact model compared with Ti + IS. The L4-L5 and L5-S1 levels showed slightly higher values with PEEK + IS, but these differences among the instrumented models were not significant. The motion difference based on the fusion mass at the adjacent levels was at most 3%. All instrumentation cases generated a 55% higher facet contact force at the lower adjacent level (L4-L5) compared to that of the intact model during 26° extension and the largest increment was detected at the upper adjacent level (L2-L3) in the Ti + IS. Instrumentation with Ti + IS markedly increased the stress in the intervertebral disk at the upper adjacent level, while the stress with PEEK + IS appeared largest at the lower adjacent level. CONCLUSIONS: Posterior instrumentation with semi-rigid rods may lower the incidence of disk and facet degeneration in the upper adjacent segment compared to rigid rods. On the other hand, the possibility of facet degeneration will be similar for all instrumentation devices in the lower adjacent segment in the long-term. The stiffness difference between rigid and semi-rigid rods on the changes in the adjacent motion segments was more crucial than amount of fusion mass.
目的：本研究旨在比较单节段浮动融合后使用后路半刚性或刚性固定对相邻节段的生物力学影响，并评估融合质量对生物力学差异的影响。
方法：建立并验证了详细的非线性 L1-S1 有限元模型。然后，在 L3-L4 水平上通过不同的固定技术重建了五个模型：带椎间间隔体的刚性固定（Ti + IS）、带大椎间间隔体的刚性固定（Ti + IS_all）、带椎间间隔体的半刚性固定（PEEK + IS）、带大椎间间隔体的半刚性固定（PEEK + IS_all）和仅半刚性固定（PEEK）。对直立位、前屈和伸展运动进行了分析。
结果：在 L1-L2 和 L2-L3 节段，与 Ti + IS 相比，PEEK + IS 使节段间旋转和核压力增量较小。L4-L5 和 L5-S1 水平的 PEEK + IS 值稍高，但这些仪器模型之间的差异不显著。相邻节段融合质量的运动差异最大为 3%。与完整模型相比，所有器械固定病例在 26°伸展时，下一个相邻节段（L4-L5）的小关节接触力增加了 55%，最大增量出现在上一个相邻节段（L2-L3）的 Ti + IS 中。Ti + IS 器械固定显著增加了上一个相邻节段椎间盘的应力，而 PEEK + IS 的应力在较低的相邻节段最大。
结论：与刚性棒相比，后路半刚性棒固定可能会降低上一个相邻节段椎间盘和小关节退行性变的发生率。另一方面，在长期情况下，所有器械固定装置在下一个相邻节段发生小关节退行性变的可能性相似。刚性和半刚性棒在相邻运动节段变化中的刚度差异比融合质量更为关键。
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