腰椎髓核摘除后小关节应力分析

Stresses analysis of the facet joints of a lumbar motion segment after discectomy

[目的]研究L4、5正常腰椎节段、髓核摘除术后腰椎节段小关节的应力大小和分布情况。[方法]利用有限元软件Ansys,建立L4、5正常节段和髓核摘除术后三维有限元模型。固定模型L5椎体下终板,在L4椎体上终板施加400 N的轴向压缩载荷,并在L4椎体上终板分别向模型施加前屈、后伸和右旋转力,力矩大小均为6 Nm。分析各个状态下腰椎小关节的应力分布情况。[结果]建立了L4、5腰椎节段正常、髓核摘除术后的三维有限元模型。小关节处理为三维接触模型,线性、面接触单元,无摩擦,由上下关节突关节面及韧带结构组成。正常模型两侧小关节在右旋转时均产生较大应力,而以左侧小关节产生应力更大。髓核摘除模型在前屈、后伸、旋转时小关节的应力均增加。[结论]在腰椎不同的运动状态下,两侧小关节面各个部位的接触情况是不同的,应力大小和分布也是变化的。髓核摘除后腰椎前柱的承载功能减弱,小关节等后柱结构分担载荷增大。

[ Objective] To study the stresses value and distribution of the facet joint of the normal L4,5 segment model and that of the denucleated lumbar segment model. [ Method ] A finite element model of the intact L4.5 segment was developed through Ansys software. The property of nucleus pulposus was changed to be negligible to model lumbar discectomy through ante- rior approach. Then the finite element model of the denucleated lumbar spine segment was created. The inferior end plate of L5 was fixed. Models were subjected to 6 Nm flexion, extension or right rotation moment in combination with 400 N axial compres- sion preload. Forces were applied to the superior L4 end plate. Stresses value and distribution of the lumbar facet joint were analyzed under different loading conditions. [ Result] Finite element models of the intact L4.5 segment and the denucleated lumbar spine segment were created. The facet joint was treated as a three dimensional contact, linear frictionless problem. The facet joint was composed of the inferior and superior facet surface and ligamentous structure. Both facet joints, especially the left of the intact model produced larger stresses in right rotation. Comparing with that of the intact model, stresses of the facet joint of the denucleated model increased in flexion, extension and right rotation. [ Conclusion] The region of contact of each facet joint varies according to different loading conditions, So does the stresses value and distribution. The facet stresses of the lumbar segment increase in flexion, extension and rotation after discectomy.