A knee prosthesis comprises a femoral component for securement to a femur, the femoral component defining medial and lateral J-shaped condyles and an intercondylar groove； and a fixed bearing tibial component for securement to a tibia, the tibial component having respective bearing surfaces which are fixed with respect to both a tibial engaging component and a stabilising peg for securing the tibial component to a tibia, the respective bearing surfaces being shaped to engage with said condyles both when the knee, in use, is extended and also over a range of flexion.
