腰椎滑脱后路不同融合术式的有限元研究

Different fusions of lumbar spondylolisthesis based on a three-dimensional finite element method

目的 建立L4.5，滑脱节段的有限元模型，研究椎弓根螺钉内固定加后外侧植骨融合、椎弓根螺钉内固定加双枚椎间融合器（cage）植入及椎弓根螺钉内固定加单枚融合器植入等3种融合术式的固定节段的稳定性。方法 选择一名56岁退变性腰椎滑脱女性患者，以k节段为研究对象，采用螺旋CT对其进行层厚1．0mm的连续水平扫描，将所得图像进行轮廓提取和阈值分割后，借助Ansys9．0软件，建立L4.5滑脱节段三维非线性有限元模型。同时根据椎弓根螺钉、融合器的几何尺寸，分别建立其相应的有限元模型。在此基础上，根据临床术式将上述模型进行不同组合，分别建立椎弓根螺钉固定加后外侧植骨融合、椎弓根螺钉固定加双枚融合器植入及椎弓根螺钉固定加单枚融合器植入等3种腰椎滑脱后路融合术式的有限元模型，然后分别施加压缩、前屈、后伸、侧屈及旋转等各种生理载荷，观察各模型不同载荷下螺钉、融合器的应力分布及融合节段的角位移变化，由此比较各模型的稳定性。结果 后外侧植骨融合术式的螺钉应力和角位移明显高于椎体间融合术（P〈0．01）；椎弓根螺钉内固定加单枚融合器植入与椎弓根螺钉内固定加双枚融合器植入两组之间螺钉应力、融合器应力及固定椎体的角位移的差异无统计学意义（P〉0．05）；各模型固定节段螺钉及融合器的最大有效应力均出现于前屈时。结论 椎弓根螺钉内固定加单枚或双枚融合器植入的稳定性优于椎弓根螺钉内固定加后外侧植骨融合；对于椎体间融合，植入单枚融合器和双枚融合器的稳定性无明显差别。

Objective To develop a three-dimensional finite element model of the L4.5 spondylolisthesis and to evaluate the stability of L4.5 fused with three different approaches （posterolateral bone graft, single fusion cage, or double fusion cage combined with pedicle screw system）. Methods The L4.5 motion segment data were obtained from CT scans （at 1 mm width increments） of the lumbar spine of a 56-year-old woman. After these images were processed, a three-dimensional finite element model of the L4.5 spondylolisthesis was established by Ansys 9.0. Meanwhile, the three-dimensional finite element model of the vertebral pedicle screw and cage were established by Ansys 9.0. According to the above mentioned, the fusion model of posterolateral bone graft, single fusion cage, and double fusion cage combined with pedicle screw system were prepared by adding bone graft, single fusion cage, double fusion cage on the basis of surgery approaches, respectively. Loads used in this study were axial compressive, flexion, extension, lateral bending, and rotation forces. After the loadings were placed on all the models, the angular motions and the distribution of von raises stress of the fused segment were analyzed and compared. Results The stress of screw and the angular motions of fusion segment in posterolateral fusion model were more increased than the interbody fusion model（P〈 0.01）. But there was no statistical significant difference between single fusion cage and double fusion cage model （P 〉0.05）. Of all models of fusion, the maximal yon raises stress of screw and fusion cage were recorded in compression combined with flexion loading. Conclusion The single fusion cage or the double fusion cage combined with pedicle screw system was more stable than the posterolateral fusion. But there was no significant difference in stable between single fusion cage and double fusion cage.