A tibia plateau for a replacement joint, particularly an endoprosthesis for a human knee joint, in which the head and socket artificial joint parts have convex and concave articulation surfaces, respectively, and the articulation surfaces are arranged in pairs, so that the functional surfaces which are formed can roll against one another along a curved contact line, especially a circularly arcuate contact line, formed on each articulation surface. A gently sloping bulge (1) is formed in the area (4) adjacent the functional surfaces (2) which bulge prevents excessive rolling movement and lateral displacement of the joint parts relative to each other.