Topology Optimization Design And Finite Element Analysis Of Bone Defect Filling Blocks In Total Knee Revision

Background: Total knee revision arthroplasty is a crucial treatment for post-knee arthroplasty complications,which can effectively improve the prognosis of life of patients.The distal femoral bone defect of knee is one of the main causes for total knee revision.The materials of filling blocks are mostly titanium alloy and cobalt alloy,which have extremely high structural stiffness.The large difference in elastic modulus between these materials and the human bone often results in different degrees of stress shielding,which is one of the important reasons for the failure of total knee revision.Due to the development of material science and design processes recently,the choice of treatment methods for periprosthetic bone defects of knee joint has been enriched.Currently the prominent clinical options are porous Ti6Al4 V blocks and ultrahigh molecular weight polyethylene blocks(UHMWPE).Topology optimization technique is a mathematical method which could optimize the material distribution in the specified area under given loading conditions and constraints.Finite element analysis can simulate the real force situation,which is the prerequisite for topology optimization.Due to the development of industrial technology of these years,the reliability of numerical simulation software and the accuracy of 3D printing manufacturing have been improved.In the field of orthopedics,prostheses with microporous structure have been widely applied.The microporous structure design can effectively reduce the equivalent elastic modulus of metals,reduce stress shielding,and provide spaces for osseointegration.The combination of topology optimization techniques and microporous structure design can effectively reduce the elastic modulus of prosthesis and promote osseointegration,which paves a way for the innovative design of prosthesis.Objective: The purpose of this program is to compare the biomechanical performance of Ti6Al4 V block and ultrahigh molecular weight polyethylene block in total knee revision and to verify the biomechanical performance of porous Ti6Al4 V block by topology optimization.The topological optimized porous block could promote the osseointegration and improve patient prognosis by optimizing the material distribution and reducing the stress shielding between the block and the bone.Methods:1.Reverse reconstruction of femoral inhomogeneous model from CT data and reverse reconstruction of prosthesis model by 3D scanning of CCK prosthesis.2.Performing meshing and errors repair.3.Simulate total knee revision and place the spatial position of the prosthesis and femur.4.Apply loads and constraints to simulate the daily conditions and perform finite element analysis.5.Apply loads and constraints for the topology optimization and redesign the graded porous structure.6.Repair the topology optimized block and perform finite element analysis to verify the biomechanical performance.Results:The maximum stress of the UHMWPE block(19.97 MPa)was close to its yield stress(21 MPa)in the standing condition.Compared to the UHMWPE block group,the maximum stress in the femur of the porous Ti6Al4 V block group was 1.67% higher in the standing condition and 27.62% higher in the flexed condition.In the investigation of stress distribution,a larger area of high stress concentration was found on the UHMWPE block,and a more uniform stress distribution and fewer areas of high stress concentration were found on the porous Ti6Al4 V block.The topology optimization results showed that the peak ROI stresses were significantly higher in the TO block group than in the solid Ti6Al4 V block group(up to 47%)and the porous Ti6Al4 V block group(up to 18%).By statistical analysis(p<0.05),the highest mean stresses of ROI were found in the TO block group.The peak SED of ROI was higher in the TO block group compared to the other designs in all conditions,indicating a higher stress transfer capability of the TO block.The peak stresses in the TO block were lower than those in the original block(up to 34%)and the porous block(up to 11%),and the TO block had the fewest high stress distribution,indicating a more reliable stress transfer capability of the TO block.Conclusions:Compared with ultrahigh molecular weight polyethylene block,porous Ti6Al4 V block has its irreplaceable biomechanical advantages.The optimized graded porous Ti6Al4 V block can significantly improve the biomechanical properties of the block and reduce the stress shielding.The design approach proposed in this program can provide a reference for the design of customized prosthesis.