A prosthesis structure (1) for anchorage to the joint end of an articulatory part of a joint (11) in a human or animal body comprises an engagement element (3) which presents a flat or substantially flat engagement surface (3b) for engaging with a complementary joint end surface (14) provided at the joint end and an elongate fixture (4) connected to and spaced from the engagement surface for insertion into a complementary bore (12) provided at the joint end at a distance from the joint end surface (14). The elongate fixture forms an acute angle ( beta ) with the engagement surface (3b).
