Abstract: This invention relates to a joint prosthesis for permanent anchorage in the bone tissue of a joint in a human body, for instance a knee joint. The joint prosthesis comprises an anchorage device (3, 4; 7-10, 11) disposed to be implanted into the bone tissue at a first operation so that it remains in unloaded condition during a healing phase during which the function of the joint is not prevented and an articulation device (5, 6; 13, 12) which is arranged to be connected to the anchorage device only at a second operation after the said healing phase.