Retrospective non-randomized in-vivo comparison of different levels of femoral rollback in the ATTUNE total knee arthroplasiy system (rotating platform CR high level roll back vs. rotating platform CR low level roll back) on the basis of fluoroscopic and marker-based motion capture evaluation. How do different levels of intra-operatively observed femoral rollback correlate to postoperative kinematics under weight bearing conditions? Does the modified design of the Attune Knee System influence the extent of the femoral rollback compared to the PFC Sigma Knee System? Does the femoral rollback maintain over a period of 12 months follow up or is it reduced by, for example, remodelling of the posterior cruciate ligament?