Lumbar interbody fusion with interspinous dynamic fixation: a finite element analysis

doi:10.3969/j.issn.2095-4344.0226

Abstract

Abstract:

BACKGROUND: Degeneration of adjacent segments after lumbar fusion is a common complication. Preliminary studies have found that the use of interspinous stabilization system alone limits the excessive activity of the implant segments, decreases disc pressure and avoids the degeneration of adjacent segments. However, it is still unclear whether it is necessary to implant the interspinous stabilization system at the proximal segment of the fusion segment to prevent the degeneration of adjacent segments.

OBJECTIVE: To investigate the biomechanical properties of the adjacent segment after the lumbar interbody fusion with the interspinous dynamic stabilization system through a finite element analysis.

METHODS: The vertebrae at L₁-pelvical levels were scanned by 64 slice spiral CT, and the data were imported into the Mimics software to generate a three-dimensional (3D) surface model. The 3D solid model was established using the SolidWorks software, and the L₄_-₅ pedicle screw, interbody cage and Coflex system model were constructed in Solidworks software. Posterior lumbar interbody fusion (PLIF) model and PLIF with the Coflex interspinous dynamic stabilization model (PLIF + Coflex model) were simulated, followed by model assignment and analysis.

RESULTS AND CONCLUSION: When the models were loaded with flexion, extension, lateral flexion, and rotation loads, the bending stiffness of the PLIF and PLIF + Coflex models was close to the complete model. The maximal von Mises stress on the L_3/4intervertebral disc of PLIF + Coflex model decreased obviously and decreased most significantly under posterior extension. The maximal von Mises stress on the L_5/S₁ intervertebral disc of two models was increased compared with the complete model. The range of motion of the L_3/4of the PLIF + Coflex model was decreased under flexion, extension and rotation than that of the PLIF model, which was not obvious under lateral flexion. Therefore, the dynamic fixation of PLIF + Coflex can effectively reduce the maximal von Mises stress of the intervertebral disc and restrict the excessive activity of the proximal segment and protect the proximal adjacent segment.

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

Key words: Tissue Engineering, Intervertebral Disk, Internal Fixators, Finite Element Analysis

CLC Number:

R318

Ma Liang, Xu Yong-tao, She Yuan-ju . Lumbar interbody fusion with interspinous dynamic fixation: a finite element analysis[J]. Chinese Journal of Tissue Engineering Research, 2018, 22(23): 3647-3653.

Figures/Tables 1

2.1 加载前屈、后伸、左右侧屈及左右旋转载荷时模型的受力情况分析在加载400 N的轴向载荷，并附加7.5 N•m的前屈，后伸，左右侧屈，左右旋转载荷时，计算完整模型，PLIF模型及PLIF+L3/4 Coflex模型的整体角位移，弯曲刚度见表2。 PLIF模型和PLIF+Coflex模型的6个方向的弯曲刚度与完整模型接近。说明这两种手术方式都能有效的恢复脊柱屈伸、左右侧屈、左右旋转时的稳定性。 2.2 邻近节段椎间盘应力比较此3种模型在前屈，后伸，左右侧弯，左右旋转6种状态下的邻近L3/4及L5/S1椎间盘最大应力值如表3。 PLIF模型L3-4椎间盘最大应力值比完整模型增大。PLIF+Coflex模型的L3-4椎间盘应力值明显减小，在屈伸及旋转时降幅较明显，后伸时减小最明显，左右侧屈时降幅稍低。PLIF模型及PLIF+Coflex模型的L5/S1椎间盘最大应力都比完整模型增加，在后伸及左旋转时增加稍大。从上述邻近节段椎间盘最大应力值对比变化可见Coflex动态稳定能有效的降低屈伸及旋转时L3-4椎间盘内的应力，预防其退变，其作用在屈伸及旋转活动时较明显，在左右侧屈时影响较小，这与Coflex假体的特殊形态有关，它的固定翼设计，使得对屈伸及旋转时的过度应力起到分散保护作用，但对左右侧屈时的异常应力集中保护能力稍差。从L5/S1椎间盘最大应力值变化可以看到L4-5融合后L5/S1椎间盘应力明显增加，造成其退变风险增加，在L3-4棘突间添加稳定装置对L5/S1椎间盘应力变化影响不大。 2.3 邻近节段活动度比较各种模型在前屈，后伸，左右侧弯，左右旋转6种状态下的L3-4及L5/S1节段的活动度如表4。 PLIF+Coflex模型在前屈，左右侧屈L3-4节段活动度比完整模型增加，比PLIF模型减小。后伸时活动度比完整模型减小。左右旋转时L3-4节段活动度比PLIF模型减小，与完整模型接近。PLIF模型及PLIF+Coflex模型的L5/S1节段活动度比完整模型都明显增加，两者间相比在6种状态下变化不明显。在行L4-5 PLIF术后邻近的L3-4及L5/S1节段活动度均代偿性增加，退变风险增加。在联合行L3-4棘突间动态固定后在前屈，后伸及左右旋转时L3-4节段活动度比L4-5融合时稍减小。对于L5/S1节段活动度，L4-5 PLIF和L4-5 PLIF+L3-4 Coflex模型比完整模型都明显增加，两者间相比在6种状态下变化不明显。说明行L3-4棘突间动态固定对L5/S1节段活动度影响不大。 2.4 PLIF联合Coflex动态固定后的应力分布特点通过应力云图来观察L4-5 PLIF+L3-4 Coflex后的应力情况，见图2。从应力云图来看在屈伸，侧屈，旋转状态下，邻近的L2-3，L3-4，L5/S1关节突处都有明显的应力集中，屈伸时关节突处的应力集中最明显。内固定钉棒系统的连接棒上在各种活动状态下都有明显的应力集中。Coflex假体的U形装置最凹面处有明显的应力集中，在屈伸时最大。Coflex假体的固定翼与棘突连接处也有明显的应力集中，在左右侧屈时最明显。 "

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