Using our previously validated methodology [17 (link)], computed tomography (CT) scans of a 60 year old subject (gender: male, BMI: 25.9) were segmented using Mimics software (version 14.1, Materialise, Leuven, Belgium) to create the tibial geometry. An iterative closest point (ICP) algorithm [18 ] was used to register this tibia model with the one used to calculate muscle forces (MATLAB, Version 7.10, MathWorks Inc., Massachusetts, USA), thereby allowing mapping of the muscle attachment sites. The tibia model was prepared for implantation of an Oxford UKR mobile bearing knee (Biomet UK Ltd., Bridgend, UK) in accordance with standard operative techniques [19 ] using Boolean operations (SolidWorks CAD software, version 2011-2012, Waltham, MA, USA). A sagittal cut to a depth of 4 mm below the medial plateau of the bone was made in line with the mechanical axis of the tibia and was positioned at the medial edge of the tibial spine. At the same depth anteriorly, a transverse cut was made with a 7° posterior slope. The tibia was also truncated 100 mm below the medial plateau to reduce the overall model size. Use of a shortened tibial model has been validated previously [4 (link)].
The cuts resulted in two separate regions: the cut region and the main tibial region. In models which examined the tibia prior to UKR (hereafter referred to as the Native model), these two regions were bonded together using a tie constraint. For the simulations of the UKR, the cut portion was removed from the simulation and the main tibial region modelled with the components inserted (hereafter referred to as the Implanted model). For the Implanted model, a 1 mm cement gap was simulated between the tray and the tibia, and the tibial tray was implanted in the centre of the cut plateau. The bearing was positioned 1 mm from the wall of the tray and in the centre of the plateau along the anterior-posterior direction. The femoral component was aligned with the axis of the central peg normal to the surface of the tibial tray (Figure 1 ).
The cuts resulted in two separate regions: the cut region and the main tibial region. In models which examined the tibia prior to UKR (hereafter referred to as the Native model), these two regions were bonded together using a tie constraint. For the simulations of the UKR, the cut portion was removed from the simulation and the main tibial region modelled with the components inserted (hereafter referred to as the Implanted model). For the Implanted model, a 1 mm cement gap was simulated between the tray and the tibia, and the tibial tray was implanted in the centre of the cut plateau. The bearing was positioned 1 mm from the wall of the tray and in the centre of the plateau along the anterior-posterior direction. The femoral component was aligned with the axis of the central peg normal to the surface of the tibial tray (
