| With the aggravation of population aging,lumbar degenerative disease has become a high-risk disease endangering economy and people’s health.The biomechanical research of lumbar spine based on finite element method provides a theoretical basis for the pathological research,diagnosis and treatment.A reliable method of establishing lumbosacral model is an important prerequisite for high-precision and efficient finite element analysis of lumbar mechanics.In previous studies,the modeling method of lumbosacral was often the reverse reconstruction method based on CT.Although the geometry of the model established by this method completely followed the real structure of the human lumbosacral,it was difficult to quickly and flexibly adjust the overall dimensions or morphological characteristics according to the research needs,and the modeling process was complex and long,with limited application value.In order to solve this problem,combined with the idea of parametric design of mechanics,this research developed a scientific and reliable parametric lumbosacral finite element model and its automatic modeling program,which can quickly complete the modeling.The parametric model was used to simulate and analyze the biomechanics of posterior lumbar interbody fusion.The main contents of this study include:(1)Construction of high precision lumbosacral finite element model and the research of its mechanical characteristicsBased on CT,a high-precision L3-S1 segment lumbosacral finite element model was constructed by using a variety of model processing,meshing and finite element methods,and the mechanical characteristics of lumbosacral when human body was upright or moving in all directions were analyzed.It is found that the stress of vertebrae and intervertebral disc in the lower part is higher when standing upright,and there are great differences in the biomechanical characteristics of lumbar spine in different directions of human movement.(2)Design of parametric lumbosacral modelAccording to the structural and mechanical characteristics of each tissue in the CT reconstructed lumbosacral finite element model,a lumbosacral model with 14 control parameters was designed.The model can quickly construct a new lumbosacral model by modifying the control parameters.Based on the CT measurement data,the parametric lumbosacral model was constructed and verified.The results show that it is effective,and the change trend of mechanical properties was similar to the CT reconstruction model.It is a reliable lumbosacral finite element model establishment method.(3)Development of automatic modeling program for parametric lumbosacral modelThe automatic modeling program of parametric lumbosacral model was developed based on Solid Works API.The repeated sketching,solid modeling and other operations during modeling were written into function code and automatically executed by the program.Realized the automatic construction of vertebral model based on 14 characteristic parameters and the automatic assembly of lumbosacral model based on 7 positioning parameters.At the same time,the corresponding model can be established according to the research purpose of lumbosacral biomechanics,such as the automatic construction of posterior lumbar interbody fusion model at the specified segment.(4)Research on clinical problems depending on the lumbosacral finite element modelAiming at the problem that adjacent segments are prone to degeneration after lumbar fusion in clinic,an automatic modeling program was used to establish a posterior lumbar fusion model with L4-L5 fusion segments.Comparing the range of motion,intervertebral disc stress and facet joint stress of each segment before and after fusion under the same load,it was found that the range of motion and internal stress of fusion segment decreased significantly after fusion,but the range of motion,facet joint stress and intervertebral disc stress of adjacent segments increased in varying degrees,and the stress concentration was more obvious.The results are verified by relevant simulation and experimental data,which further defines the mechanism of adjacent segment degeneration after fusion. |
