A unicompartmental knee prosthesis for implantation in a knee joint between a femoral condyle and a corresponding tibia plateau is provided including a generally elliptical body having opposed femoral and tibial face, the body having an anterior end and a posterior end. A keel is provided on the tibial face having a generally anterior-posterior orientation, the keel having an anterior end and a posterior end, where the keel posterior end includes a distal posterior portion that extends farther toward the body posterior end compared with a proximal posterior portion of the keel posterior end.