Implant loosening and polyethylene wear in fixed-bearing knee prostheses were recognized as major causes of late failure. The mobile bearing knee have the theoretical advantages of potentially minimizing the polyethylene wear and reducing implant to bone interface stress in order to reduce the incidence of implant loosening. Therefore, the aims of this study are to prove the Vanguard deep dish rotating platform knee is at least as effective in clinical outcome as the widely used current design of knee replacement and better in long term survivorship.