Influence Of Installation Accuracy Of Unicondylar Knee Prosthesis On Polyethylene Insert Wear

Unicondylar knee replacement(UKA)is an effective method for the treatment of endstage unicondylar knee osteoarthritis.However,aseptic loosening caused by wear particles between articular contact surfaces is an important reason for the failure of UKA prosthesis.Preclinical wear evaluation is very important to evaluate wear performance and reduce the risk of prosthesis failure.However,the wear performance of UKA prostheses has been evaluated using the test criteria for total knee,and the impact of loading methods on the wear evaluation of UKA prostheses is unclear.In addition,malalignment of UKA prostheses can lead to knee biomechanical abnormalities,which can affect the wear performance and service life of the prosthesis.However,the influence of UKA prosthesis installation error on articular surface wear has not been discussed.Based on ISO 14243-1: 2009,finite element model and wear model of mobile-and fixedbearing UKA prostheses were established.The wear prediction method under total knee loading mode was evaluated by indirect verification,and the wear difference between mobile-and fixed-bearing UKA prostheses was further studied.The results showed linear wear depth of fixed-bearing UKA prosthesis was 1.5 times that of mobile-bearing UKA prosthesis.But the wear volume of mobile-bearing UKA prosthesis was 5.4 times that of fixed-bearing UKA prosthesis.The backside wear volume of mobile-bearing UKA prosthesis accounted for 70%of its total wear volume.Therefore,mobile-bearing UKA prosthesis had lower contact stress but larger wear volume than fixed-bearing UKA prosthesis.The finite element model and wear model provided a technical means for the wear performance evaluation of UKA prosthesis and the selection of UKA prosthesis by surgeons.Considering the difference between unilateral loading mode and total knee loading mode,finite element model and wear model of UKA prosthesis were established respectively,and the effects of two loading modes on the evaluation of contact mechanics and wear of UKA prosthesis under ISO test condition and measured data condition were compared.The results showed that regardless of ISO test condition or measured data condition,the wear volume of the UKA insert under unilateral loading mode is greater than that under total knee loading mode.Therefore,the total knee loading mode did not accurately reflect the wear of UKA prosthesis.In addition,the predicted wear under measured data condition were larger than those under ISO test condition.This study suggested that a more reasonable test method should be established for UKA prosthesis.Combined with the musculoskeletal multi-body dynamics model,finite element contact mechanics model and wear model of UKA,the effect of varus-valgus installation error of UKA femoral,joint line installation error of UKA prosthesis,posterior slope angle of tibial component on the insert surface wear was studied.The results showed that compared with the neutral position,contact stress and wear volume of the UKA prosthesis were not significantly influenced by femoral varus-valgus malrotation.Compared with the neutral position,the increase of UKA joint line would increase the contact stress and wear volume of the insert surface,while the decrease of UKA joint line was just the opposite.The contact stress and wear volume on the insert surface of UKA could be reduced with a certain increase of the posterior slope angle of the tibial component.This thesis provided a method for the wear evaluation of UKA prosthesis and a theoretical basis for surgeons to understand the mechanism of the influence of the installation error on the wear life of UKA prosthesis.