The optimal element size, material property distributions and modeling methods for finite element modeling of lumbar vertebra

To investigate the effects of element size and type, material property distributions of vertebral cancellous bone and simulation methods of cortical bone structure on the finite element (FE) results during the finite element modeling of lumbar vertebral body. Based on QCT images of lumbar spine, 22 FE models of L2 without posterior structure were built by using 6 element sizes (0.5, 1.0, 1.5, 2.0, 2.5, 3.0 mm), 2 kinds of material property distribution methods of cancellous bone, 2 heterogeneous material distribution methods of cancellous bone (150, 300) and 2 cortical bone modeling methods. The maximum displacement, strain energy, average stress and axial stiffness of these models were obtained to analyze and verify the results. When the element size was 0.5 mm, the axial stiffness among the models with 10, 150 and 300 kinds of heterogeneous materials showed obvious differences; for the vertebral cancellous bone with 150 kinds of materials, the average stress appeared no distinct variation under different element sizes; the average stress of the model using the outermost hexahedral elements to simulate cortical bone structure was larger than that of the model appending the skin to the outmost. It is more reasonable and effective to build the FE model of lumbar vertebral body with the method by using 0.5 mm element size, 8-noded hexahedral elements, 150 kinds of heterogeneous materials, and using the outermost hexahedral elements to simulate the cortical bone structure. The research findings will lay a foundation for building subject-specific FE models of lumbar vertebral body on a large scale in future.