Design Of Block Augmentation To Treat Tibial Bone Defects In Total Knee Arthroplasty Based On Topology Optimization And Finite Element Analysis

Background: Total knee arthroplasty is one of the most effective surgical operations for pain relief and functional recovery in patients with knee osteoarthritis.Varus deformity of the knee and defect of the tibial plateau frequently occur in patients with severe knee osteoarthritis.When severe uncontained bone defects are encountered,it can be difficult to maintain the stability.At this point,th1 e application of block augmentation can effectively fill the defects and maintain the stability of the implants.However,most of the current blocks are made of solid metal,it will inevitably increase the stress shielding,and the osteointegration cannot be achieved.Topology optimization technique is a design method which can optimize the material distribution and remove the redundant materials in a given area.It can optimize the material distribution of implant,reduce the elastic modulus of implant,and lower the stress shielding.Finite element analysis technique,complementary to the topology optimization technique,can simulate the real stress situation,which means that loads and constrains are applied according to the biomechanical characteristics of the implant.T1his study aimed to topologically optimize the block augmentation in total knee arthroplasty based on finite element analysis to improve its biomechanical performance and reduce stress shielding.Through optimizing the material distribution,the functionally gradient porous block will be achieved based on areas with different material properties to further reduce the elastic modulus and weight of the block,and to improve patient prognosis.Methods: 1.The inhomogeneous tibia model was reconstructed based on CT scan of a patient who suffered from knee osteoarthritis.Reconstruction of the implants was accomplished by inversely scanning the solid implants.2.Gait analysis was conducted to acquire the maximum force and angle of the tibia plateau through the whole gait cycle.3.All the models were adjusted to the correct position to simulate the operation.The complete finite element models were established.The force and constrain were added.Minimum compliance topology optimization under the constraint of volume fraction was added to the block.4.According to the optimization results,the gradient porous design was conducted to the reserved area and the removed area of the block.15.The finite element model of optimized block was established.Finite element analysis was conducted to compare the stresses of block and tibia.6.The gradient porous block was 3D printed.Results: Compared with the original block,the optimized gradient porous block achieved in 40% weight reduction.The maximum stress of the original metal block was 8.90 MPa,and that of the optimized one was 7.87 MPa,indicating a decrease of 11.6%.The maximum strain energy density in the proximal tibia of the original group was 1.43 k Pa,and that in the optimized group was 1.93 k Pa,corresponding to an increase of 35.0%.The average stress of all the nodes in the original block(2.18 ± 1.05 MPa)was significantly larger than that in the optimized block(1.90 ± 0.88 MPa)(p < 0.05).The maximum stress in the proximal tibia of the original group was 2.37 MPa,and that in the optimized group was 2.81 MPa,indicating an increase of 18.6%.The proximal medial tibia that contacted with the metal block was divided into three parts: anterior,medial,and posterior part.The average stress of the anterior,middle,and posterior parts in the o1 riginal group was 0.42 ± 0.25,0.43 ± 0.23,and 0.15 ± 0.13 MPa.The average stress of the anterior,middle,and posterior parts in the optimized group was 0.44 ± 0.27,0.56 ± 0.30,and 0.23 ± 0.19 MPa.The stress of each part in the optimized group was significantly larger than that in the original group(p < 0.05).The maximum stress of the tibial stem in the original group was 28.0 MPa,and that in the optimized group was 28.7 MPa,indicating a slight increase of 2.5%.No considerable difference was found in the comparison.Conclusions: The optimized gradient porous block augmentation could effectively improve the biomechanical performance between the block and bone.It could also reduce stress shielding and improve patient prognosis.This procedure might provide a reference for the design of customized threedimensional–printed prostheses.