Comparison of Interface Stresses and Strains for Onlay and Inlay Unicompartmental Tibial Components

Introduction: There are two main designs used for unicompartmental tibial components. The first design, an all plastic component called an inlay, preserves bone on the outer edge of the tibia which is feasible using a robotically-controlled burring tool. Also, the depth of resection is small, preserving the strongest cancellous bone which is near the surface. The second design, called an onlay, resects the entire condyle and includes a metal backed plate which rests on the resected tibia. This component requires more bone removal but metal-backing has previously been shown to distribute the load more uniformly. The purpose of this study was to investigate the hypothesis that while inlay components require less bone removal, the peak stresses and strains at the surface of the bone will be greater when compared to onlay components.