Subject-specific modelling of Total Knee Arthroplasty could be an efficient method to preoperatively evaluate surgical options. In particular, the question of the necessity of patellar resurfacing is still a debatable issue. The aim of this work was to validate a numerical model of Total Knee Arthroplasty using an instrumented robotic knee simulator equipped with kinematic sensors. The patellar kinematics during a loaded knee flexion were measured with the knee simulator and compared with the values predicted by the model. The mean absolute difference between measured and predicted patellar translations and rotations was respectively 1.4 mm and 2.4 deg. This numerical model will be later used for subject-specific predictions of patellar kinematics and strain state after Total Knee Arthroplasty.