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Abstract：
BACKGROUND: Although it is critical to understand the accelerated degeneration of adjacent segments after fusion, the biomechanical properties of the spine have not been thoroughly studied after various fusion techniques. This study investigates whether four Roussouly\'s sagittal alignment morphotypes have different biomechanical characteristics after different single- or double-level spinal fixations.
METHODS: The parametric finite element (FE) models of Roussouly\'s type (1-4) were developed based on the radiological data of 625 Chinese community population. The four Roussouly\'s type models were reassembled into four fusion models: single-level L4-5 Coflex fixation model, single-level L4-5 Fusion (pedicle screw fixation) model, double-level Coflex (L4-5) + Fusion (L5-S1) model, and double-level Fusion (L4-5) + Fusion (L4-5) model. A pure moment of 7.5 Nm was applied to simulate the physiological activities of flexion, extension, lateral bending and axial rotation.
RESULTS: Both single-level and double-level spinal fixation had the greatest effect on lumbar range of motion, disc pressure, and annulus fibrosis stress in flexion, followed by lateral bending, extension, and axial rotation. In all models, the upper adjacent segment was the most influenced by the implantation and bore the most compensation from the fixed segment. For Type 2 lumbar, the L4-L5 Coflex effectively reduced the disc pressure and annulus fibrosis stress in adjacent segments compared to the L4-L5 Fusion. Similarly, the L4-L5 Coflex offered considerable advantages in preserving the biomechanical properties of adjacent segments for Type 1 lumbar. For Type 4 lumbar, the L4-L5 Coflex did not have superiority over the L4-L5 Fusion, resulting in a greater increase in range of motion at adjacent segments in flexion and extension. The difference between the two fixations was not apparent in Type 3 lumbar. Compared to the single-level Fusion, the changes in motion and mechanics of the lumbar increased after both the double-level Coflex + Fusion and Fusion + Fusion fixations, while the differences between two double-level fixation methods on adjacent segments of the four lumbar models were similar to that of the single-level fixation.
CONCLUSIONS: Type 3 and Type 4 lumbar have good compensatory ability and therefore allow for a wider range of surgical options, whereas surgical options for small lordotic Type 1 and Type 2 lumbar are more limited and severe.
METHODS: The parametric finite element (FE) models of Roussouly\'s type (1-4) were developed based on the radiological data of 625 Chinese community population. The four Roussouly\'s type models were reassembled into four fusion models: single-level L4-5 Coflex fixation model, single-level L4-5 Fusion (pedicle screw fixation) model, double-level Coflex (L4-5) + Fusion (L5-S1) model, and double-level Fusion (L4-5) + Fusion (L4-5) model. A pure moment of 7.5 Nm was applied to simulate the physiological activities of flexion, extension, lateral bending and axial rotation.
RESULTS: Both single-level and double-level spinal fixation had the greatest effect on lumbar range of motion, disc pressure, and annulus fibrosis stress in flexion, followed by lateral bending, extension, and axial rotation. In all models, the upper adjacent segment was the most influenced by the implantation and bore the most compensation from the fixed segment. For Type 2 lumbar, the L4-L5 Coflex effectively reduced the disc pressure and annulus fibrosis stress in adjacent segments compared to the L4-L5 Fusion. Similarly, the L4-L5 Coflex offered considerable advantages in preserving the biomechanical properties of adjacent segments for Type 1 lumbar. For Type 4 lumbar, the L4-L5 Coflex did not have superiority over the L4-L5 Fusion, resulting in a greater increase in range of motion at adjacent segments in flexion and extension. The difference between the two fixations was not apparent in Type 3 lumbar. Compared to the single-level Fusion, the changes in motion and mechanics of the lumbar increased after both the double-level Coflex + Fusion and Fusion + Fusion fixations, while the differences between two double-level fixation methods on adjacent segments of the four lumbar models were similar to that of the single-level fixation.
CONCLUSIONS: Type 3 and Type 4 lumbar have good compensatory ability and therefore allow for a wider range of surgical options, whereas surgical options for small lordotic Type 1 and Type 2 lumbar are more limited and severe.
摘要：
背景：尽管了解融合后相邻节段的加速退变至关重要，在各种融合技术之后，脊柱的生物力学特性尚未得到彻底研究。这项研究调查了四种Roussouly矢状位排列形态类型在不同的单或双水平脊柱固定后是否具有不同的生物力学特征。
方法：基于625个中国社区人口的放射学数据，开发了Roussouly类型（1-4）的参数有限元（FE）模型。四个Roussouly类型的模型被重新组装成四个融合模型：单级L4-5Coflex固定模型，单级L4-5融合（椎弓根螺钉固定）模型，双层Coflex(L4-5)+Fusion(L5-S1)模型，和双层融合(L4-5)+融合(L4-5)模型。施加7.5Nm的纯力矩来模拟屈曲的生理活动，扩展,横向弯曲和轴向旋转。
结果：单级和双级脊柱固定对腰椎活动范围的影响最大，圆盘压力,和弯曲时的纤维环应力，其次是横向弯曲，扩展,和轴向旋转。在所有型号中，上相邻段受植入影响最大，固定段补偿最大。对于2型腰椎，与L4-L5融合相比，L4-L5Coflex有效降低了相邻节段的椎间盘压力和环纤维化应力。同样，L4-L5Coflex在保留1型腰椎相邻节段的生物力学特性方面具有相当大的优势。对于4型腰椎，L4-L5Coflex没有优于L4-L5融合，导致在弯曲和伸展的相邻节段的运动范围更大的增加。在3型腰椎中，两种固定方式之间的差异不明显。与单级融合相比，在双水平Coflex+融合和融合+融合固定后，腰椎的运动和力学变化增加，而两种双级固定方法在四个腰椎模型的相邻节段上的差异与单级固定相似。
结论：3型和4型腰椎具有良好的代偿能力，因此允许更广泛的手术选择，而小脊柱前凸1型和2型腰椎的手术选择更为有限和严重。
方法：基于625个中国社区人口的放射学数据，开发了Roussouly类型（1-4）的参数有限元（FE）模型。四个Roussouly类型的模型被重新组装成四个融合模型：单级L4-5Coflex固定模型，单级L4-5融合（椎弓根螺钉固定）模型，双层Coflex(L4-5)+Fusion(L5-S1)模型，和双层融合(L4-5)+融合(L4-5)模型。施加7.5Nm的纯力矩来模拟屈曲的生理活动，扩展,横向弯曲和轴向旋转。
结果：单级和双级脊柱固定对腰椎活动范围的影响最大，圆盘压力,和弯曲时的纤维环应力，其次是横向弯曲，扩展,和轴向旋转。在所有型号中，上相邻段受植入影响最大，固定段补偿最大。对于2型腰椎，与L4-L5融合相比，L4-L5Coflex有效降低了相邻节段的椎间盘压力和环纤维化应力。同样，L4-L5Coflex在保留1型腰椎相邻节段的生物力学特性方面具有相当大的优势。对于4型腰椎，L4-L5Coflex没有优于L4-L5融合，导致在弯曲和伸展的相邻节段的运动范围更大的增加。在3型腰椎中，两种固定方式之间的差异不明显。与单级融合相比，在双水平Coflex+融合和融合+融合固定后，腰椎的运动和力学变化增加，而两种双级固定方法在四个腰椎模型的相邻节段上的差异与单级固定相似。
结论：3型和4型腰椎具有良好的代偿能力，因此允许更广泛的手术选择，而小脊柱前凸1型和2型腰椎的手术选择更为有限和严重。
