Finite element analysis and zoning of stress in lumbar 1 vertebra

English Keywords:Lumbar spine  Stress zoning  Loading  Finite element

English Abstract:

  【Abstract】 Objectives: To explore the stress distribution of the cortical bone and cancellous bone in the L1 vertebral body under different levels of load and different motion states by finite element analysis, and to establish the stress zone. Methods: One volunteer underwent plain CT scan of thoracolumbar vertebrae. The original data of CT were obtained by DICOM and imported into finite element software such as Mimics, Geomagic, SoliderWorks, HyperMesh, Abaqus and so on. The normal thoracolumbar vertebra model(T11-L2) was constructed, and the mechanical load was applied evenly on the upper edge of the vertebral body. All motion states produced under load 500N and bending moment 7.5N·m were in the group, those produced under 600N and 7.5N·m were in the β group, and those produced under 700N and 7.5N·m were in the γ group. The L1 vertebral body was divided equally into upper and lower parts in the sagittal view, with the upper part marked as area A, and the lower part as area B. Six segments were divided equally in concentric circle from the center to the edge of the vertebral body, and the upper and lower parts formed a three-dimensional circular cylinder. From the outer edge to the center, they were marked as A1, A2, A3, A4, A5, A6, B1, B2, B3, B4, B5, B6, totally 12 parts. The load data of cortical bone and cancellous bone in the above 12 regions were uniformly collected in α, β and γ groups, and the stress values in the adjacent areas of cortical bone and cancellous bone were tested by pairwise t test. The two adjacent regions with statistically significant difference were separated into different regions, and the two adjacent regions with no statistically significant difference were merged into one region, and the final stress zones were obtained. Results: In group α, the average stress of cortical bone and cancellous bone in A1 region was significantly different from that in A2 region, there was no significant difference between that in A2 region and A3 region, and there was significant difference between that in A3 region and A4 region. There was no significant difference among those in A4, A5 and A6. The law of region B was the same as that of region A. In β group, the A region and B region of cortical bone met the statistically significant rule of α group. There were significant differences between A4 and A5, B4 and B5 in cancellous bone, and the others were the same as those in α group. In γ group, the differences between cortical bone and cancellous bone in A4 region and A5 region, in B4 region and B5 region were statistically significant, and the others were the same as those of α group. According to the statistical law, the L1 vertebra was divided into six regions: A1(AⅠ), A23(AⅡ), A456(AⅢ), B1(BⅠ), B23(BⅡ) and B456(BⅢ). Among them, the stress distribution in AⅡ region was the most concentrated and called the core stress zone; the stress distribution in AⅠ, BⅠ and BⅡ was the second, and called the main stress zone; the stress distribution of AⅢ and BⅢ was the least, and called the secondary stress zone. Conclusions: The stress distribution of the L1 vertebral body is relatively fixed and presents a certain regularity. The core stress area, the main stress area and the secondary stress area are gradually weakened, which is helpful for the prediction and evaluation of clinical fracture types.