Tibiofemoral conformity variation offers changed kinematics and wear performance of customized posterior-stabilized total knee arthroplasty.

PURPOSE: Posterior-stabilized (PS)-total knee arthroplasty (TKA) can be applied in any of several variations in terms of the tibiofemoral conformity and post-cam mechanism. However, previous studies have not evaluated the effect of the condylar surface radii (tibiofemoral conformity) on wear in a customized PS-TKA. The present study involved evaluating the wear performance with respect to three different conformities of the tibiofemoral articular surface in a customized PS-TKA by means of a computational simulation.

METHODS: An adaptive computational simulation method was developed that conduct wear simulation for tibial insert to predict kinematics, weight loss due to wear, and wear contours to results. Wear predictions using computational simulation were performed for 5 million gait cycles with force-controlled inputs. Customized PS-TKA designs were developed and categorized as conventional conformity (CPS-TKA), medial pivot conformity (MPS-TKA), and anatomical conformity (APS-TKA). The post-cam design in the customized PS-TKA is identical. We compared the kinematics, contact mechanics, and wear performance.

RESULTS: The findings revealed that APS-TKA exhibited the highest internal tibial rotation relative to other TKA designs. Additionally, the higher contact area led to there being less contact stress although it did not directly affect the wear performance. Specifically, MPS-TKA exhibited the lowest volumetric wear.

CONCLUSIONS: The results of the present study showed that tibiofemoral articular surface conformity should be considered carefully in customized PS-TKA design. Different wear performances were observed with respect to different tibiofemoral conformities. Even though APS-TKA exhibited an inferior wear performance compared to MPS-TKA, it proved to be better in terms of kinematics so its functionality may be improved through the optimization of the tibiofemoral articular surface conformity. Additionally, it should be carefully designed since any changes may affect the post-cam mechanism.