Methods: 100 knees in 97 patients are stratified according to age and gender and randomized into two groups fixed bearing (FB) with 52 knees and mobile bearing (MB) with 48 knees. All receive the same posterior cruciate retaining implant but the tibial tray and bearing (B. Braun Aesculap Columbus CR and RP) by two experienced surgeons and follow an identical rehabilitation regime. Physical examinations are performed in a double-blinded manner before the operation and three, six and twelve months thereafter, using the Oxford and Knee Society scoring systems.