A femoral component (2) of a knee joint prosthesis has a bearing surface (4) for articulation with a tibial bearing surface and an opposite bone facing surface (6). The bone facing surface has anterior (18), posterior (20), distal (22), anterior chamfer (24) and posterior chamfer (26) portions. Medial (42, 52, 356) and lateral rails (40, 50, 350) are provided on the distal portion or on at least one of the anterior chamfer portion and posterior chamfer portions of the bone facing surface so that there is at least one recess (46, 54, 354, 360) between the rails.
