Mobile-bearing unicompartmental knees facilitate decreased polyethylene wear and restoration of knee kinematics. The purpose of this study was to quantify tibial strains during bearing mobility in UKA. Composite tibiae were implanted with cemented metal-backed tibial components and coated with photoelastic material, allowing "full-field" strain analysis. A fully congruent mobile polyethylene bearing was loaded in six separate locations on the tibial tray, simulating bearing translation during knee motion. Strains were noted to be greatest in the anteromedial tibia, 2 cm distal to the joint line, which correlates with the area occasionally noted to have residual pain following UKA. This study demonstrates the important role that bearing movement plays in load distribution throughout the tibia after UKA and may illuminate a biomechanical process of tibial remodeling that influences pain and implant loosening.