不同弯矩作用下腰椎正常与压缩骨折模型的有限元分析

Finite element analysis of normal and compressed fracture models under different bending moments

目的建立L1~3正常腰椎模型和L2椎体压缩骨折的模型,并进行有限元分析,观察在不同弯矩应力下两种模型的椎间盘及关节突的力学分布差异。方法取一位健康男性志愿者腰椎三维CT扫描图像,导入Mimics 16.0软件中,并建立L1~3椎间盘、纤维环和髓核模型,并在正常模型基础上切除L2椎体上半部分,模拟L2椎体压缩骨折(I度),再导入Hypermesh 13.0软件中进行网格划分,后导入Abaqus 14.2软件中,进行体网格划分和建立韧带结构,并在L1上表面施加500N垂直向下的力,再施加大小为5、10和15Nom的弯矩,模拟腰椎做不同幅度的前屈及后伸运动,观察L1~L2(L1~2)椎间盘、L2~L3(L2~3)椎间盘、L1关节突、L2关节突和L3关节突应力最大值及其分布情况。结果椎间盘分析结果提示,在所有工况下骨折模型压应力均比正常模型压应力高,在前屈体位比后伸体位应力高。椎间盘最大应力分布,在工况一到工况七下:正常模型L1~2椎间盘分布规律为由椎间盘的右前方转变为椎间盘的左后方,骨折模型L1~2椎间盘分布规律为由左前方到右后方;L2~3椎间盘的正常模型和骨折模型分布规律均为由右后方到左前方,再到右后方。关节突分析结果提示,在工况一到工况七,两模型的所有关节突最大应力值均表现为由大到小,再到大的过程。关节突最大应力分布无规律,大部分分布于右侧下关节突。结论有限元力学分析显示腰椎压缩骨折后,伤椎的椎间盘和关节突的压应力较正常椎体增大,提示骨折后可能脊柱退变加速。相对关节突,椎间盘的应力分布较规律,关节突应力分布的不规律可能提示骨折后脊柱后柱退变加速部位具有不确定性。

Objective To establish a normal L1-3 model and a L2 vertebral compression fracture model,and to observe the differences in the stress＇ s distribution of mechanical facet joints and intervertebral discs at different bending moments of two models by using finite element analysis. Methods The study took a healthy volunteer＇s lumbar three-dimensional CT scan images data,imported to Mimics 16. 0,and established lumber 1 to lumber 3 finite element model,including： intervertebral disc,nucleus pulposus and annulus fiber,and removed the L2 vertebra upper part based on the normal model to simulate L2 vertebra compression fracture model（I degree）,then imported to Hypermesh 13. 0 for meshing. After that,those models were imported to Abaqus 14. 2 to create volume meshing and ligamentous structures. A 500 N vertical force was applied on the L1 upper surface,and then the bending moments of5 Nom,10 Nom and 15 Nom were applied to simulate different magnitudes of flexion and extension. Finally,and the maximum stress and its distribution on L1-2 disc,L2-3 disc,L1 to L3 facet joints were observed. Results The results showed that the compression fracture model,in all conditions,had higher stress than the normal model,and the maximum flexion stress was higher than extension. On the maximum disc stress distributions,from the first working condition to the seventh working condition,the maximum stress＇ s distribution of L1-2 of normal model was turning from at right-front of the disc to the left-rear,and the maximum stress＇ s distribution of L1-2 fracture model was from the front-left to right-rear. While the maximum stress＇ s distribution of L2-3 disc of the normal model and the vertebral compression fracture model were regularly from the right-rear to left-front,and finally,to the right-rear. Facet joint results showed that,from the first working condition to the seventh condition,all facet joints of two models＇ maximum stress values were expressed as descending,while then ascending. The facet joint maximum stress distribution was irregular. The majority of stress located in the lower right side of the facet. Conclusion Finite element analysis suggests that after lumbar compression fractures,the compressive stress of intervertebral disc and facet joint are higher than those of the normal ones,indicating that vertebral compression fracture may accelerate the spinal degeneration. Comparing with facet joint stress distribution,the disc has more regular one. The facet joint＇s irregular stress distribution may indicate that accelerated degeneration site in the posterior spinal column becomes uncertain after fracture.