Numerical Simulation Study On The Effects Of Structures And Materials Of Tibial Components On Tibial Bone Remodeling Behavior

Total knee arthroplasty(TKA)is one of the most effective treatments for knee joint diseases.Due to the increase of the elderly population,the number of people choosing to be treated with TKA will inevitably rise.However,stress shielding and stress concentration,caused by implantation of tibial components,may lead to inadequate tibial bone stock,which triggers pain and increases the risk of tibial components loosening.Design features of tibial components,such as structures and materials can affect stress shielding and stress concentration directly.Accordingly,recent researches mainly focus on design features.In this study numerical simulation was performed to evaluate the influence of structures and materials of tibial components on tibial bone remodeling behavior.This dissertation was composed of two parts:In the first part,finite element models of 3D tibias and tibial components were developed and incorporated with bone remodeling algorithm,to quantify the effect of geometric length and materials of cementless stems on tibial bone remodeling behavior.Three groups of lengths were investigated(i.e.,110,60,and 30 mm),and four materials(i.e.,titanium(Ti),flexible ‘iso-elastic' material,and two functionally graded materials [FGMs])were selected for each group.Two FGMs were the mixture of Ti and bioactive hydroxyapatite(FGM I)and the mixture of Ti and bioglass(FGM II).The distributions of tibial bone mineral density,von Mises stress,and interface shear stress were obtained,to investigate the influence of geometric length and materials of stems on stability of tibial components,stress shielding,and stress concentration.The results showed that for the length,the long stem produced more serious stress shielding and stress concentration than the short stem,but it could provide better mechanical stability due to less interface shear stress;for the material,FGM I,compared with Ti,could reduce stress shielding and stress concentration and decrease the risk of loosening;moreover,the change of elastic modulus had a significant influence on stress shielding only when the material property of the stem was close to that of bone;finally,it was concluded that the material had more pronounced effect on bone remodeling behavior than the length.Given that the selection of length was usually determined with the intended fixation and anatomy of patients,the improvement on materials of stems would be more flexible and feasible.For a minimally invasive surgery,the destruction of tibial bone tissue should be reduced;besides,asymmetric tibial components with smaller volume fractions for TKA should be designed due to asymmetries of the tibial structures and of physiological loads.In the second part,structures of stems and fins of cement tibial components were optimized by incorporating finite element analysis(FEA)with topology optimization.For the design domain,constraints of volume fractions at high,middle,and low levels(i.e.,70%,50%,and 30%),and objective function of the maximum stiffness were defined.Influence of the obtained geometries on tibial mechanical environments was explored,and the ideal structure was achieved.The results showed that when the distance from the region of cancellous bone to the tibial tray was less than 20 mm,all three groups of tibial components after optimization could reduce stress shielding;when the distance was at 30 mm-40 mm,these groups could remarkably relieve stress concentration,especially for the group with the constraint of 70% volume fraction.So the optimized structure,constrained by the high volume fraction(about 70%),was more reasonable.The difference in the structure of original and optimized tibial components revealed that removal of fins and the anterolateral region of stems was beneficial to relieve the stress shielding at the tibial anterolateral region and stress concentration at the tibial bottom region.In this dissertation,firstly,the influences of geometric length and material of cementless stems on tibial bone remodeling behavior were investigated by incorporating FEA with bone remodeling algorithm;Then,finite element models of tibias and cement tibial components were developed and incorporated with topology optimization,to quantify the effect of structure of tibial components,optimized by constraints of volume fractions,on tibial mechanical environments.This study can serve as a theoretical basis for the design of tibial components,and can help to improve the service life of tibial components and to reduce the pain of patients.