The displacement of patellar components, such as dislocation or subluxation, causes polyethylene wear and further induces metallosis of the metal-backed patella. We compared two different patellar components, onset(Miller-Galante I) and inset(Whiteside-Ortholoc I)type, to understand the differences in patellar tracking according to their designs. Patellar prosthesis position in 43 primary total knee arthroplasties was evaluated with patellar tilt, patellar displacement from the center of the trochlear groove, medial placement, patellar thickness, and joint line height. For the MG(Miller-Galante I)group, the patellar displacement was laterally 50.0% and for the Ortholoc group, it was 33.3%. In the MG group, 4 cases of revision of the patellar component due to excessive polyethylene wear were performed, but there was no excessive wear of polyethylene in Ortholoc group. One of the primary factors which influence tracking of the patellofemoral joint is the difference in design between the patellar component and the femoral component. But in the opinion of the authors, the slope or lateral displacement of the patellar component have no correlation with each other under radiological measurements. However, the inset-type patellar component is a design that maintains the bony flange within the lateral flange, therefore relieving the shear stress and rotational forces loaded on the patellofemoral joint and protecting the metal-backing from exposure. Thereby, even if dislocation or subluxation of the patellar component should occur, polyethylene wear or metallosis caused by excessive wearing can be minimal.