A mobile bearing tibial implant is described which comprises a tibial component and a mediscal bearing component. The tibial component comprises a tibial plate having a proximal face and a distal face. A tibial post extends from the distal face of the tibial plate which in use will anchor the tibial plate to the proximal end of a resected tibia. The tibial compent additionally includes a generally rectangular tibial projection extending upwardly from the proximal face of the tibial plate, the central longitudinal plane of the said tibial projection being co-linearly located on the sagittal plane passing substantially through the center of the knee. The meniscal bearing component has a substantially flat distal face for glidable seating on the tibial plate and a proximal face configured to receive in use an articulating condylar surface of a femoral component. The meniscal component has a recess therein opening on the distal face of the component, the recess being shaped to receive the tibial projection and to allow the meniscal bearing component to rotate about a center of rotation passing through the tibial projection but to prevent or limit anterior/posterior translation of the meniscal bearing component on the tibial plate.