【Abstract】 ObjectiveTo construct a finite element model of a complex of human internal fixation and thoracolumbar spine, and to investigate the stress of the finite element complex model under different daily motions. MethodsA finite element model of human thoracolumbar spine receiving internal fixation was constructed using relevant softwares including Mimics, Geomagic studio and HyperMesh. According the reliable standard weight of 60kg supplied by kinematics database Orthoload, loading conditions were defined as the mechanical feedback of subjects’ vertebral bodies under different daily motions and then were imposed on the 3D finite element model established. The stresses of superior and inferior endplates of normal vertebral body and postoperative thoracolumbar internal fixation were recorded under different loads. 3D finite element analysis about the finite element model was performed. ResultsThere was obvious difference in the stress between the endplates and the internal fixation under four motions (including squat, walking up/down steps, normal walking and standing). In the finite element model of thoracolumbar spine, the maximal stresses decreased in the order of squat, walking up/down steps, normal walking and normal standing. The stress of endplate when squat was higher than that when normal standing. The same trend existed in the stress of the internal fixation system. Extremely obvious stress concentration was observed in the root and connecting rods of pedicle screws when squat. And the internal fixation system had a risk of fixation failure caused by fatigue. ConclusionSimulation study on 3D finite element mechanics can effectively evaluate the stress of human thoracolumbar spine, and can provide the theoretical basis for the stability of thoracolumbar internal fixation.

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