不同载荷下腰1椎体内应力分布规律的有限元分析

Finite element analysis on the stress distribution in the lumbar 1 vertebral boby under different loadings

目的：观察腰1（L1）椎体在不同载荷作用下椎体内应力分布情况,探讨其应力分布规律及临床意义。方法：选取1例27岁健康男性志愿者,以层厚1mm进行T12~L2脊柱节段CT扫描,将原始数据存盘。运用3D软件、Auto CAD系统及ANSYS 6.0有限元软件建立正常人体胸腰段（T12~L2）运动节段的三维有限元模型。在T12椎体上表面施加不同等级的压力（400N、600N、800N、1000N、1200N）,模拟脊柱的轴向压缩载荷;在T12椎体上表面施加不同等级压力（400N、600N、800N、1000N、1200N）的同时再施30N·m的弯矩,模拟脊柱的屈曲压缩载荷。将连接L1椎体上下终板凹面最低点的连线7等份,在此基础上将L1椎体中的松质骨划分为7个具有统计节点的层面,每个统计层面划分成9个统计区（椎体前部A1、A2和A3区,椎体中部M1、M2和M3区,椎体后部P1、P2和P3区）。测量L1椎体松质骨中间3个层面9个统计区的平均应力值,将9个统计区划分成6个组,分别为Ⅰ组A1、A2、A3,Ⅱ组M1、M2、M3,Ⅲ组P1、P2、P3,Ⅳ组A1、M1、P1,Ⅴ组A2、M2、P2,Ⅵ组A3、M3、P3。比较同一等级载荷下9个统计区的应力分布情况,并对6个组内的松质骨应力值进行两两配对t检验,分析L1椎体内不同载荷作用下应力分布情况。结果：轴向加载时同一等级载荷下,Ⅲ组内P2松质骨平均应力值与P1、P3比较,Ⅳ组内P1与A1、M1比较,Ⅴ组内P2与A2、M2比较,Ⅵ组内P3与A3、M3比较,差异均有统计学意义（P〈0.05）;而Ⅰ组、Ⅱ组内的数据经两两比较均无统计学差异（P〉0.05）;椎体后部P区（P1,P2,P3）的应力值与M区、A区比较最大,其中P2区应力最大。屈曲加载时同一等级载荷下,Ⅰ组内A2与A1、A3比较,Ⅱ组内M2与M1、M3比较,Ⅲ组内P2与P1、P3比较,Ⅳ组内A1与M1、P1比较,Ⅴ组内A2与M2、P2比较,Ⅵ组内A3与M3、P3比较,差异均有统计学意义（P〈0.05）;Ⅰ组内A1与A3比较,Ⅱ组内M1与M3比较,Ⅲ组内P1与P3比较,Ⅳ组内M1与P1比较,均无统计学差异（P〉0.05）;椎体前部A区（A1,A2,A3）的应力值与M区、P区比较最大,A2区应力最大。结论：L1椎体在不同载荷作用下,松质骨内存在着应力分布的集中趋势;轴向加载时应力集中的部位靠近椎体后缘中央,屈曲加载时应力集中的部位靠近椎体前缘中央。

Objectives： To investigate the stress distribution in the body of lumbar I（L1） vertebral under the different types of compressive loading, and to study the stress distribution and its clinical meaning. Methods： Thin-slice CT scanning was performed on the thoracolumbar junction（T12-L2） of a 27-year-old healthy male volunteer. The raw data of the CT scans were stored for further analysis. The 3D finite element model of the thoracolumbar junction（T12-L2） was established by using the 3D software, Auto CAD system and ANSYS 6.0. This model was assigned for two different types of test, the axial compressive loading group and anteflexion compressive loading group. In the axial compressive loading group, different loads（400N, 600N, 800N, 1000N, 1200N） were exerted on the upper surface of T12 to simulate the axial stress. While in the anteflexion compressive loading group, same loads but with additional 30N.m torque were exerted on the upper surface of T12 to simulate anteflexion stress. For statistic purpose, the ligature between the lowest points of vertebral endplates concaves was divided into 7 portions, and then the cancellous bone of the L1 vertebra was divided into 7 layers, and each layer was separated into 9 zones. The average stress was measured on the 9 zones in each layer of the 3 internal cancellous bone layers. Then the 9 zones were divided into 6 groups. Group I： A1, A2, A3; group U： M1, M2, M3; group III： P1, P2, P3; group IV： A1, M1, P1; group V： A2, M2, P2; group VI： A3, M3, P3. Under the same loading, the stress comparisons within the 9 zones were made. The two-paired t test was made on these values of the 6 groups, to study the stress distribution in L1 vertebral boby under the different loads. Results： In the axial compressive loading group, under the same loading, among the group m： P2 with P1, P3, group VI： P1 with A1, M1, group V： P2 with A2, M2, group VI： P3 with A3, M3, all showed statistical significance. But as for the data of group l, II, there was no significant difference by the two-paired t test. In the posterior area of vertebra, the stress value of P zone was the maximum compared with M zone, A zone. The stress value of P2 was maximum. In anteflexion com- pressive loading group, under the same loading, among group I ： A2 with A1, A3, group 1I： M2 with M1, M3, group llI： P2 with P1, P3, group VI： A1 with M1, P1, group V： A2 with M2, P2, group VI： A3 with M3, P3, all showed statistical significance. Among group I： A1 with A3, group ll： M1 with M3, group Ill： P1 with P3, group VI： M1 with P1, all showed no significant difference. In the anterior area of vertebrae, the stress value of A zone was the maximum compared with M zone, P zone. The stress value of A2 was the maximum. Conclusions： Under different loading, the stress concentration in the L1 vertebra cancellous bone is evident. Under the axial compression loading, the stress concentrates in the middle of posterior edge of the vertebral body. While under the anteflexion compression loading, the stress concentrates in the middle of anterior edge of the vertebral body.