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

Background: Unicondylar 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. Methods: The influence of the tibial slope on wear was investigated in mobile bearing unicondylar knee prosthesis. This was positioned with four different tibial slopes (-4 degrees, 0 degrees, 4 degrees, 8 degrees) 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. Findings: Wear was significantly reduced with an increasing tibial slope (0 degrees: 3.46 mg/million cycles, SD: 0.59, 4 degrees slope: 152 mg/million cycles, SD: 0.06, 8 degrees slope group: 0.99 mg/million cycles, SD: 0.42). An anterior slope of -4 degrees also reduced wear (2.08 mg/million cycles, SD: 037). 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. Interpretation: Increasing 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 degrees 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. (C) 2013 Elsevier Ltd. All rights reserved.