内镜下不同入路腰椎融合术对腰椎生物力学效能影响的有限元分析

Finite element analysis of the effect of endoscopic lumbar fusion on the biomechanical performance of the lumbar spine

目的:通过有限元分析方法探讨内镜下经椎间孔入路腰椎椎间融合术(endoscopic transforaminal lumbar interbody fusion,Endo-TLIF)与内镜下后路腰椎椎间融合术(endoscopic posterior lumbar interbody fusion,Endo-PLIF)对腰椎生物力学效能的影响。方法:采集1例24岁健康男性志愿者腰椎L3~L5节段CT扫描数据,建立包含L3~L5椎体皮质骨、松质骨及后柱结构的三维有限元模型,通过与以往研究数据对比验证模型有效性。回顾性分析在广州中医药大学第一附属医院行内镜下腰椎融合术(endoscopic lumbar interbody fusion,Endo-LIF)治疗的40例患者的影像学及临床数据,根据手术入路不同分为Endo-TLIF组(n=19)和Endo-PLIF组(n=21),测量融合器位置、角度并计算关节突关节保留百分比,作为确定有限元手术模型融合器放置位置及角度的依据,最终构建Endo-TLIF+45°融合器、Endo-TLIF+60°融合器、Endo-PLIF+45°融合器、Endo-PLIF+60°融合器4种有限元手术模型。观察融合节段的活动度以及终板、融合器、螺钉、棒、骨-螺钉界面的最大峰值应力。结果:所有手术模型与完整模型相比,手术节段的活动度均显著降低。在所有手术模型中,融合节段终板的最大峰值应力在前屈工况下均显著增加。Endo-PLIF模型的骨-螺钉界面最大峰值应力在左、右旋转工况下较Endo-TLIF模型显著增加(23%~84%)。60°融合器模型的终板及融合器峰值应力均高于45°融合器模型。在左、右旋转工况下,Endo-PLIF模型内固定物和终板的应力较Endo-TLIF模型明显增加。结论:相较于Endo-TLIF,Endo-PLIF手术后内固定周围应力显著增加,尤其在旋转活动方面应力增加幅度更为明显,内固定失败风险更高。

Objectives:To investigate the impact on lumbar spine biomechanical performance of endoscopic lumbar interbody fusion(Endo-LIF)via two approaches,namely endoscopic transforaminal lumbar interbody fusion(Endo-TLIF)and endoscopic posterior lumbar interbody fusion(Endo-PLIF)through finite element analysis.Methods:The L3-L5 CT scan data of a 24-year-old healthy male volunteer was collected to establish a three-dimensional finite element model containing cortical bone,cancellous bone and posterior structure of L3-L5 vertebrae.The validity of the model was verified by comparing with other previous studies.The clinical and radiological data of 40 patients underwent Endo-LIF were analyzed retrospectively,and according to different operational approaches,the patients were divided into Endo-TLIF group(n=19)and Endo-PLIF group(n=21).The cage positions and angles of the patients were measured,and the facet joint preservation ratios were calculated to determine the cage placing positions and angles in constructing finite element surgical models.Finally,four finite element surgical models were constructed as Endo-TLIF+45°cage,Endo-TLIF+60°cage,Endo-PLIF+45°cage,and Endo-PLIF+60°cage.The range of motion(ROM)at the fusion segment and the maximum von Mises stress of endplates,cages,screws,rods,and bone-screw interfaces were calculated.Results:The ROMs of fusion segments in all surgical models reduced significantly compared with the intact model.The maximum von Mises stress of endplates in the surgical segment increased significantly under the flexion conditions in all surgical models.The maximum von Mises stress at the bone-screw interfaces of the Endo-PLIF model was significantly increased compared with the Endo-TLIF model under left and right rotation conditions(23%-84%).The maximum von Mises stress of the endplate and cage in the 60°cage models was higher than that in the 45°cage models.In the Endo-PLIF model,the stress of internal fixations and endplates was significantly increased compared with the Endo-TLIF model under left and right rotation conditions.Conclusions:Comparing with Endo-TLIF,Endo-PLIF has significantly higher maximum von Mises stress around the internal fixations,especially under rotational conditions,with greater risk of internal fixation failure.