The invention relates to a floating bearing knee joint prosthesis having a fixed tibial post used for replacing the articulating knee portion of a femur and a tibia. The floating bearing knee joint prosthesis includes a femoral component, a tibial component, a bearing member and a guide post. The femoral component includes an engagement member, a first femoral bearing surface and a second femoral bearing surface. The tibial component includes a tibial bearing surface. The bearing member includes a first bearing surface which is operable to articulate with the first femoral bearing surface, a second bearing surface which is operable to articulate with the second femoral bearing surface and a third bearing surface which is operable to articulate with the tibial bearing surface. The guide post extends from the tibial component and is operable to be engaged by the engagement member of the femoral component such that upon engagement, the femoral component forces the bearing member to move posteriorly relative to the tibial component.