Survivorship in total knee arthroplasty (TKA) is multifactorial and dependent upon alignment, ligament balance, patient characteristics, and implant factors. The contribution of each factor leading to implant loosening is not well known. This study defined the effect of femoral component sizing relative to tibial size on loading patterns in the proximal tibia. Changes in strain were measured in tibiae implanted with appropriately sized metal-backed tibial components loaded with 2 sizes of femoral components. Significant increases of shear strain up to 126% were measured in peripheral regions of the tibia when loaded with a larger vs a smaller femoral component. Increased peripheral loading in the proximal tibia could predispose to a higher risk of cancellous overload and failure. Limiting stress concentrations in the periphery of the proximal tibia by considering sizing relationships between femoral and tibial components may decrease osseous strains and the likelihood of bony overload in TKA.