有限元模型分析髓核摘除术后腰椎生物力学特性变化

目的采用三维有限元模型分析方法,探讨腰椎间盘突出症髓核摘除术对腰椎生物力学特性的影响。方法采用新型CAD方法精确建立腰椎L4～L5活动节段有限元模型,构建正常模型、退变模型、髓核摘除即刻模型和瘢痕长入模型,分别模拟正常椎间盘、退变椎间盘、髓核摘除术后即刻和术后中长期随访时的椎间盘,并在压缩、屈曲、伸展、前剪及后剪5种载荷条件下对4组模型进行生物力学测试。结果 (1)各种载荷下退变模型的腰椎节段刚度较正常模型提高;(2)髓核摘除即刻模型的刚度较退变模型减小,但较正常模型提高;(3)瘢痕长入模型腰椎节段刚度大幅回升并超过退变模型;(4)髓核摘除即刻模型在屈曲、后伸和后剪载荷下关节突接触力减小,瘢痕长入模型则表现为在后伸、前剪和后剪载荷下关节突接触力增加;(5)各种载荷下退变模型后向膨出度较正常模型明显减小,髓核摘除即刻模型后向膨出度一定程度回升,但其纤维环内环会发生"内向膨出"。结论腰椎间盘髓核摘除术可在术后不同时段对腰椎运动节段生物力学特性产生不同影响,髓核摘除术后即刻对腰椎稳定性和后部结构应力影响较小,而髓核摘除中长期后则可有腰椎运动节段变硬和关节突的应力增加。

Finite element model analysis of lumbar biomechanical characteristics after nucleus discectomy

ObjectiveTo use three-dimensional finite element model analysis for studying the lumbar biomechanical characteristics following nucleus discectomy in a patient with lumbar intervertebral disc protrusion. MethodsA novel CAD method was adopted to accurately create the finite element models of L4/5 segment, including the models for normal disc, degenerated disc, denucleated disc immediately after operation (denucleated model), and denucleated disc after a longer time period (scar growth model). Furthermore, the biomechanical parameters of the four models were examined under five different loads, namely, compression, flexion, extension, forward and backward shear loads. Results(1)Under the five loads, the stiffness of degenerated model was increased compared with that of the normal disc under all 5 different loads. (2)The stiffness of denucleated model was decreased than that of degenerated disc and increased than that of the normal disc. (3)The stiffness of scar growth model was enhanced and even surpassed that of the degenerated model due to the fact that the scar tissue filled the intradisc cavity. (4) The facet contact force was decreased under flexion, extension, and backward shear loads in denucleated model, and were increased under extension, forward and backward shear loads in scar growth model. (5) The backward bulge in the degenerated model was obviously slighter than that in the normal model. The backward bulge of denucleated model increased to some extent, and its inner annulus fibrous had inward bulging. ConclusionNucleus discectomy has different effects on the biomechanics of lumbar motion segment in patients at different time points after operation. The impacts on lumbar stability and posterior structure are small immediately after nucleus discectomy, and the lumbar motion segment may stiffen and the stress of articular process may increase after a longer time period following nucleus discectomy.