Increase of tibial slope reduces backside wear in medial mobile bearing unicompartmental knee arthroplasty

BackgroundUnicondylar knee arthroplasty is a good alternative for patients in monocompartmental osteoarthritis. The revision rate in unicondylar knee arthroplasty is higher than in total knee arthroplasty. The influence of the tibial slope on wear in unicondylar knee arthroplasty has not been investigated so far.MethodsThe influence of the tibial slope on wear was investigated in mobile bearing unicondylar knee prosthesis. This was positioned with four different tibial slopes (− 4°, 0°, 4°, 8°) in a knee wear simulator simulating the human gait in a plane according to ISO 14243-2:2002(E). After this a kinematic analysis was performed and the inlays were observed under reflected-light-microscopy.FindingsWear was significantly reduced with an increasing tibial slope (0°: 3.46 mg/million cycles, SD: 0.59, 4° slope: 1.52 mg/million cycles, SD: 0.06, 8° slope group: 0.99 mg/million cycles, SD: 0.42). An anterior slope of − 4° also reduced wear (2.08 mg/million cycles, SD: 0.37). Kinematic analysis revealed a reduced translation between the inlay and the tibia with an increasing tibial slope. The backside of the inlays of the 4° and 8° slope group showed less wear pattern when observed under reflected-light microscopy.InterpretationIncreasing the tibial slope led to a reduced translation between the inlay and the prosthesis in the analysed mobile-bearing unicondylar knee arthroplasty and with this to a reduced backside wear. A tibial slope between 4 and 8° can be recommended in mobile UKA to reduce wear, however, the influence on the ligaments has to be considered and needs to be investigated in further studies.