A fixed-bearing prosthesis (10) includes a femoral component (12) having a medial condyle surface (32) and a lateral condyle surface (30). A bearing (16) has a medial bearing surface (28) configured to articulate with the medial condyle surface of the femoral component, and a lateral bearing surface (26) configured to articulate with the lateral condyle surface of the femoral component. A tibial tray (14) is secured to the bearing. The tibial tray has a platform (18) with an elongated stem (20) extending downwardly from a lower surface (22) thereof. A posterior buttress (44) extends along a posterior section of the perimeter of the tray's platform, and an anterior buttress (64) extends along an anterior section of the perimeter of the tray's platform. Differently-sized tibial trays are interchangeable with differently-sized bearings.
