Numerical Simulation Study On The Effects Of Titanium Alloy Porous Femoral Stem On Stress Shielding Of Bone Tissue

Hip replacement is a relatively mature medical treatment for femoral joint injury and inflammation pain.Femoral stem is an important part of the artificial hip joint,which can increase component stability by reducing micromotion.The great stiffness difference between femoral stem material and bone material will cause stress shielding phenomenon,resulting in aseptic loosening of the prosthesis.The femoral stem with porous structure can effectively reduce the difference in elastic modulus between femoral stem and femur,which can alleviate stress shielding effect.3D printing technology can print complex metal implants with porous structure according to the actual conditions of patients,which provides the possibility of manufacturing femoral stems with porous structures.In this study,a 3D finite element model of human femur was developed based on the CT images of the femur,and the validity was verified.An individualized solid femoral stem model was constructed according to the outline of femoral medullary cavity.A corresponding model was established according to the fixed type femoral stem,which is produced in batches and is widely applied in clinic at present.The two models were simulated by static numerical simulation,and was loaded according to the characteristics of human one-legged stance in a static state.The maximum von Mises stresses and stress distributions of the two models were compared and analyzed.Three structures were selected,including Cube,Gyroid(G)and Diamond(D)of triply periodic minimal surface(TPMS).The equivalent stiffness matrixes of five porosity(55%,60%,65%,70% and 75%)of each structure were calculated by the homogenization method.In the aspect of femoral stem model design with porous structure,the personalized solid femoral stem was combined with Cube,G and D porous structures.The uniform fully and non-fully porous femoral stems were established,and the porosity of the porous structure was uniformly distributed.In addition,the transverse gradient fully and non-fully porous femoral stems,the longitudinal gradient fully and non-fully porous femoral stems were established,and the porosity of the porous structure was gradient distributed.The equivalent stiffness matrix was assigned to the porous part.Forty-eight kinds of individual porous femoral stem-femoral models were established for static numerical simulation.The average von Mises stress,average interface shear stress and maximum strain energy density of the femur was compared.It was shown that compared with the fixed femoral stem,the individualized femoral stem can highly conform to the shape of the femur and obtain better initial stability.Compared with solid femoral stems,Cube,G and D porous stems significantly increased the average von Mises stress proximal to the femoral and stem interface.The higher porosity of the porous structure,the greater average von Mises stress,indicating that the porous structure with high porosity can significantly reduce the stress shielding effect of the proximal femur.The statics simulation results show that the D porous stem and the longitudinal gradient porous stem can significantly improve the average von Mises stress of the proximal femur compared with the Cube and G porous stems with the same porosity.The average shear stress of the proximal femoral interface of the D uniform full porous femoral stem changes more slowly than that of other parts of the femur,which is more conducive to improving the stability of the proximal prosthesis.The maximum strain energy density of the proximal femur of the D uniform full-porous femoral stem with the porosity of 75% is larger,which is more beneficial to stimulating the growth of bone tissue of the proximal femur.The individualized femoral stem designed based on the shape of the femoral medullary cavity has better initial stability of the prosthesis.The D fully porous femoral stems with higher porosity have the least effect on the stress shielding of bone tissue,which is beneficial to the femoral stem and bone tissue sharing the loads.In this study,the individualized femoral stems with porous structure were designed for patients undergoing hip replacements,providing theoretical basis for the selection and design of femoral stem in clinic.