Topological Optimization Design And Biomechanical Advantages Verification Of 3D-printed Prosthesis For Reconstruction Of The Proximal Tibia

The number of total knee replacement(TKA)surgery in our country is on a rising trend year by year.In TKA surgery patients,some of them involved in a wide range of the proximal tibia defect and the surrounding soft tissue attachment points are severely damaged,such as the patients undergo wide resection of bone giant cell tumors in proximal tibia.Nowadays the conventional hinge knee prostheses are widely used for the reconstruction in these cases in the clinical.However,according to literature reports,the 8-year survival rate of the hinged knee prosthesis used for proximal tibial reconstruction is only 47%.The limited design of the hinge may cause stress concentration between the long stem and the residual bone,overloading of the interface,poor biomechanical stability and other defects.Therefore,in the previous study,our research group used 3D printed customized proximal tibia prosthesis combined with constrained condylar knee(CCK)prosthesis to replace the traditional tumor hinged knee prosthesis.Due to the fact that the prosthesis is made of titanium alloy material,the elastic modulus of the prosthesis is greatly different from the bone tissue,which leads to the stress shielding effect between the prosthesis and bone.The stress shielding may cause bone resorption,prosthesis loosening,and fractures around the prosthesis.In order to optimize the biomechanical properties of the prosthesis,researchers have explored ways to improve the prosthesis by changing the prosthesis material or optimizing the structural design in recent years,and topology optimization(TO)is an important structural optimization method.TO technology is a method to optimize the material distribution in the design area according to the load cases,constraint,and objects.It is mostly applied to the design of bridge,the structural optimization in the field of aerospace and automobile manufacturing.The material distribution is reduced to achieve the purpose of weight reduction under the condition of stability and structural strength.In recent years,with the continuous development of 3D printing and finite element analysis technology,TO has been gradually applied in implant design of medicine,among which,it is most widely applied in orthopedics.The researchers use TO technology to optimize the distribution of implant materials under the biomechanical conditions of daily life,the implant weight and the stress shielding effect can be reduced,so as to reduce postoperative complications.In this study,the existing biomimetic reconstruction block of the proximal tibia was optimized by TO.The finite element analysis and biomechanical experiment were used to analyze and verify the results.In the tibia simulation modeling,the material properties of the tibia were assigned by using the method of heterogeneous assignment,and then the prosthesis and tibia were assembled to simulate the operation process.To simulate the load case,the maximum force on tibial platform in the whole gait cycle was obtained by the gait analysis system.In the topological optimization stage,the volume fraction of the block was constrained,and the minimum strain energy was taken as the optimization objective.In the post-optimization stage,gradient grid design was given according to different element densities.The biomechanical experiment under the same load case was completed by using the universal mechanical testing machine.The accuracy of the finite element analysis results was verified by measuring and analyzing the stress at multiple positions on the surface of the tibia.Results showed that the weight of proximal tibia bionic block reduced by 77%after TO.In finite element analysis of TO prosthesis,the stress of distal stem decrease,the peak stress decrease by 39.1%.More stress transferred to tibia,which reduced the stress concentration on the distal stem.Also,the micro motion of the stem decreased by 49.7%,which reduce the risk of loose and pain.In the finite element analysis of the tibia,the stress and strain energy density of the tibia increased after optimization,and the peak values increased by 39.6% and 61.5% respectively,which indicated that the stress shielding between the prosthesis and bone was significantly reduced.In the biomechanical experiment,the surface stress distribution of the tibia was similar to the results of the finite element analysis,which verified the accuracy and reliability of the finite element analysis.The results of this study demonstrate that the topologically optimized proximal tibial prosthesis can reduce weight,improve the biomechanical environment,reduce the stress shielding effect between the prosthesis and bone,and also reduce the risk of prosthesis loosening,periprosthetic fracture,and postoperative pain.