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

English Keywords:Lumbar vertebra  Loading  Stress distribution  Finite element

English Abstract:

  【Abstract】 Objectives: To investigate the stress distribution in the body of lumbar 1(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 Ⅱ: 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 Ⅲ: P2 with P1, P3, group Ⅵ: P1 with A1, M1, group Ⅴ: P2 with A2, M2, groupⅥ: P3 with A3, M3, all showed statistical significance. But as for the data of group Ⅰ, 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 compressive loading group, under the same loading, among group Ⅰ: A2 with A1, A3, group Ⅱ: M2 with M1, M3, group Ⅲ: 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 Ⅱ: M1 with M3, group Ⅲ: 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.