Numerical Simulation And Experimental Study Of The Micromotion Behavior At The Porous Tibial Implant–bone Interface

With the increasing trend of younger patients undergoing total knee arthroplasty,bone cement–fixed prosthesis,as the gold standard for replacement,has long–term stability caused by problems such as toxicity of bone cement,aging and degeneration of bone cement,and rupture under cyclic loading.The deficiency is no longer suitable for young patients who need long–term solid fixation,and cementless fixation has become a research hotspot.The initial stability of the biological fixation prosthesis depends on the interfacial micromotion coefficient.A sufficiently high friction coefficient can reduce the interfacial fretting,which is conducive to the ingrowth of bone into the porous structure of the prosthesis to form a long–term and reliable biological fixation.The existing researches are mainly experimental research and simulation research.The experimental research cannot reveal the specific mode of the fixed interface micromotion,and the error is large,while the simulation research does not simulate the difference and difference of the influence of various complete gaits on the initial stability of the prosthesis.Effects of porosity,prosthesis of different geometries on the initial stability of implants.In this paper,taking the knee joint as the research object,aiming at the initial stability of the biological tibial prosthesis,a finite element model of the total knee joint prosthesis including the tibia is established to simulate the walking gait process,the squatting gait process,and the sitting step.The effects of six motions on the initial stability of the implant,including gait process,standing gait process,up–stair gait process,and down–stair gait process,were analyzed.Relationship between peak body interface micromotion and gait cycle.Based on the optimal micromotion interval(0～50 μm)for osseointegration and the micromotion interval(above 150 μm)that promotes the growth of fibrous tissue and reduces the interface strength,the area ratio of the interface micromotion below 50 μm and the interface micromotion interval are calculated and extracted.For the area ratio above150 μm,the effect of the gait cycle on the interface stability was analyzed.Prosthesis design is also an important factor affecting implant stability.Biological tibial prostheses with different geometric designs and trabecular bone structures with different porosity were established to analyze the influence of walking gait on interface micromotion.The main contents of research include:(1)Using MIMICS,GEOMAGIC and HYPERMESH software,the assembly models of tibia-total knee joint prosthesis and tibia-cement total knee joint prosthesis were established and meshed,and MIMICS and ABAQUS software were used to assign material properties and define boundaries of tibia and other parts According to the conditions,the peak contact stress on the upper surface of the tibial pads of the cementfixed and bio-fixed prostheses under walking gait was calculated with the gait cycle,the model and loading method were verified,and reasonable boundary conditions were determined.(2)The effect of asynchronous motion on the initial stability of biological fixation prostheses was investigated.The results show that the change law of the axial displacement of the tibial tray with the gait cycle is consistent with the change of the axial load with the gait cycle,and the axial displacement,the collapse height of the proximal tibia,and the contact stress of the proximal tibia are positively correlated;the interface micromotion is mainly concentrated.At the distal end of the prosthesis and the anterior edge of the platform;the axial displacement of the bio–fixed prosthesis is slightly larger than that of the bone–cemented method,but the maximum difference remains within 10%,although the initial stability of the bone–cement is better than that of the bio–fixed fixation method is strong.Considering the long–term stability of the biological fixation method is better than the bone cement fixation method,the biological fixation method can be the first choice for young patients.(3)The friction coefficients of trabecular bone structures with different porosity were measured by the experiment and increased with the increase of porosity.The greater the porosity of the trabecular bone structure,the more uneven the surface structure,and the greater the friction coefficient;the high friction coefficient provides sufficient initial stability,and the stiffness of the tibial plateau of the bone trabecular structure decreases,which can reduce stress shielding to a certain extent.the porous structure provides growth space for bone tissue cells,enhances the interface strength,and improves the initial stability of the implant.(4)The geometry of the tibial prosthesis affects the distribution and size of the interface micromotion.The motion of the knee joint is extremely complex,and the micromotion of the bone–prosthesis interface is the result of the coupling of axial load,internal and external rotation,front–to–back translation,and flexion and extension.The axial load is the highest,and the internal and external rotation is large;the tri–rib prosthesis and the fixed angle screw trabecular prosthesis effectively reduce the interface micromotion caused by the internal and external rotation and the subsidence of the medial platform.