腰椎单侧椎板间开窗双侧减压术后腰椎生物力学改变的有限元分析

Finite element analysis of the biomechanical changes following unilateral laminotomy for bilateral decompression in lumbar spine

目的:采用有限元分析方法评估单侧椎板间开窗双侧减压手术(unilateral laminotomy for bilateral decompression,ULBD)后L4~L5节段的生物力学状态,为ULBD治疗腰椎退变性疾病提供理论依据。方法:提取1名健康志愿者腰椎CT薄层扫描数据,应用高保真三维有限元方法建立L4~L5正常模型、ULBD术后模型和椎板间开窗单侧减压(lumbar fenestration,LF)术后模型,对所有模型完全固定L5椎体下终板,在L4上终板施加500N轴向载荷及在前屈、后伸、左侧屈、右侧屈、左旋转、右旋转六个方向分别施加10N·m的弯矩载荷。对比分析不同载荷下三种模型的L4/5椎间盘压缩高度、椎间活动角度、椎间盘内应力分布和关节突间压力等生物力学特性。结果:正常模型在六个方向的活动度均在既往尸体实验研究测量结果的区间内,所建模型有效。正常模型、ULBD术后模型和LF术后模型在500N轴向载荷下椎间盘压缩高度分别为0.74mm、0.85mm、0.85mm。叠加10N·m的弯矩载荷在前屈、后伸、左侧屈、右侧屈、左旋转、右旋转六个方向上,正常模型椎间活动度分别为6.1°、4.2°、5.1°、4.6°、2.9°、2.6°,ULBD术后模型分别为6.5°、4.8°、6.0°、5.2°、3.2°、2.9°,LF术后模型分别为6.4°、4.6°、5.6°、5.1°、3.0°、2.8°;三种模型椎间盘内应力分布无明显差异,最大von Mises应力都分布在椎间盘受压侧外纤维环处;前屈、后伸、左侧屈、右侧屈、左旋转、右旋转时正常模型椎间盘最大von Mises应力分别为0.52、0.66、0.81、0.87、0.46、0.40MPa,ULBD术后模型分别0.64、0.76、1.06、1.13、0.60、0.64MPa,LF术后模型分别0.65、0.80、1.00、1.06、0.66、0.65MPa。左、右旋转状态下关节突间有显著的压力,正常模型左、右旋转状态时的压力分别为60N、69N,ULBD术后模型为30N、87N,LF术后模型为79N、120N。结论:ULBD术后腰椎间盘压缩高度、椎间活动度、椎间盘内应力和关节突间压力均有明显改变,与LF手术相比,ULBD对腰椎生物力学稳定性影响较小。

Objectives:To evaluate the biomechanical state of the L4-L5 segment after unilateral laminotomy for bilateral decompression(ULBD)surgery using finite element analysis,providing a theoretical basis for the treatment of lumbar degenerative diseases with ULBD.Methods:Thin-slice CT scan data from the lumbar spine of a healthy volunteer were extracted,and high-fidelity three-dimensional finite element methods were applied to establish normal L4-L5 model,post-ULBD surgery model,and post-lumbar fenestration(LF)surgery model.The L5 vertebral body′s lower endplate was fully fixed in all the models,and a 500N axial load was applied at the L4 upper endplate,along with a 10N·m bending moment load in six directions of flexion,extension,left lateral bending,right lateral bending,left rotation,and right rotation.Comparative analysis of the biomechanical characteristics such as intervertebral disc compression height,intervertebral range of motion(ROM),stress distribution within the intervertebral disc,and facet joint pressure was conducted under different loads for the three models.Results:The ROMs under six directions of movements were within the range of the measured results of previous cadaveric studies,verifying that the normal model was valid.Under the 500N axial load,the intervertebral disc compression heights for the normal model,post-ULBD and post-LF surgery models were 0.74mm,0.85mm,and 0.85mm,respectively.With an additional 10N·m bending moment load,the intervertebral ROM in flexion,extension,left lateral bending,right lateral bending,left rotation,and right rotation for the normal model were 6.1°,4.2°,5.1°,4.6°,2.9°,and 2.6°,respectively;for the post-ULBD model,they were 6.5°,4.8°,6.0°,5.2°,3.2°,and 2.9°,respectively;and for the post-LF model,they were 6.4°,4.6°,5.6°,5.1°,3.0°,and 2.8°,respectively.There was no significant difference in the stress distribution within the intervertebral disc for the three models,with the maximum von Mises stress occurring at the outer annulus fibrosus on the compressed side of the disc.The maximum von Mises stress in the intervertebral disc for the normal model under flexion,extension,left lateral bending,right lateral bending,left rotation,and right rotation was 0.52MPa,0.66MPa,0.81MPa,0.87MPa,0.46MPa,and 0.40MPa,respectively;for the post-ULBD model,it was 0.64MPa,0.76MPa,1.06MPa,1.13MPa,0.60MPa,and 0.64MPa,respectively;and for the post-LF model,it was 0.65MPa,0.80MPa,1.00MPa,1.06MPa,0.66MPa,and 0.65MPa,respectively.Significant facet joint contact pressure was observed under left and right rotation,with the normal model showing contact pressure of 60N and 69N,the post-ULBD model showing 30N and 87N,and the post-LF model showing 79N and 120N.Conclusions:After ULBD surgery,there is an increase in lumbar intervertebral disc compression height,intervertebral ROM,stress within the intervertebral disc,and facet joint pressure.Compared with LF surgery,ULBD has a smaller impact on the biomechanical stability of the lumbar segment.