人体胸腰段三维有限元力学的仿真研究

Simulation study on 3D finite element mechanics of human thoracolumbar spine

目的建立人体内固定-胸腰段复合体有限元模型,探讨不同日常动作下有限元复合体模型受力情况。方法利用Mimics、Geomagic studio、Hyper Mesh等相关软件建立进行内固定手术的人体胸腰段三维有限元模型,按照运动学数据库Orthoload中真实测定的60 kg标准体重,受试者不同日常动作下椎体力学反馈作为加载条件,将其施加于构建完毕的三维有限元模型中,记录各作用下正常椎体上下终板及经过手术的胸腰段内固定受力情况。结果对有限元模型进行三维有限元分析,结果显示四种动作(蹲起、上下台阶、正常行走、正常站立)终板和内固定受力情况具有较大差异。胸腰椎有限元模型中最大应力值按照蹲起、上下台阶、正常行走和正常站立逐渐下降,蹲起时终板受力远高于正常站立位。内固定系统受力具有同样趋势,其中蹲起时椎弓根螺钉根部及连杆应力集中现象极为明显,具有疲劳损伤致内固定失效风险。结论三维有限元力学仿真能够有效评估人体胸腰段受力情况,同时为胸腰椎内固定系统稳定性提供理论依据。

Objective To 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. Methods A finite element model of human thoracolumbar spine receiving internal fixation was constructed using relevant softwares including Mimics, Geomagie 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. Results There 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 thoraeolumbar 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. Conclusion Simulation 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.