Finite Element Analysis Of Fixed Platform Unicompartmental Knee Arthroplasty At Different Tibial Retrograde Osteotomy Angles

Objective:The knee joint was modeled by finite element method,and the optimal posterior Angle of tibial prosthesis in fixed bearing-unicompartmental knee arthroplasty FB-UKA was studied.It also provides reference for the selection of posterior inclination Angle of clinical FB-UKA operation.Method:A healthy adult male was selected for CT and MRI scanning of his knee joint.The imaging files were imported into Mimics in DICOM format for preliminary processing,image threshold was adjusted,and the bone structure and ligament of the adult male knee joint were screened out using the regional growth tool.The vacant pixel holes were manually filled and the excess parts were erased.The 3D knee joint model file was exported in stl format.After that,the model was imported into Geomagic Studio 2020 for further smoothing,nail removal,and feature elimination,and the polygonal model was re-triangulated,after which the curved sheets were constructed and trimmed,the curved surfaces were fitted,and the generated curved models were saved in stp format.Then enter Solidworks 2020 and store all parts as SLDPRT format for assembly to obtain a complete knee joint assembly model.Perform FB-UKA operation simulation on the model,and finally obtain the postoperative models of tibial prosthesis with 3°,5°and 7° retroposition.After the model interference inspection,enter into Ansys software.The material properties of each structure were defined and assigned.The contact stress between femur prosthesis and shim,the Von Mises stress of tibial cortex and spongy bone,and the contact stress of lateral meniscus and tibial cartilage were simulated after FB-UKA operation under the condition of different posterior Angle of tibial components.Results:In the two models of knee extension and 30° flexion after FB-UKA surgery,the contact stress peak between femoral prosthesis and gasm reached 10.93 Mpa when the posterior inclination of tibial prosthesis was 3°,the Von Mises stress was the maximum between the tibial cortex and the articulatory bone,and the contact stress peak was the minimum when the posterior inclination was 7°.The Von Mises stress of cortical bone and cancellous bone of tibia was minimal.When the posterior inclination of tibial prosthesis is 5°,the above observation indexes are slightly increased compared with the7° regression model,but both of them are significantly different from the 3° regression model.Conclusions:During fixed platform unicompartmental knee arthroplasty,the contact stress and relative displacement between the tibial prosthesis are small when the posterior inclination Angle is 5° and 7°,and the contact stress is obviously increased when the posterior inclination Angle is 3°.Therefore,physicians should try to avoid too small posterior inclination Angle of the tibial prosthesis during FB-UKA surgery,and the placement of the tibial prosthesis can refer to the posterior inclination Angle of 5° or 7°.