A joint prosthesis system has two implant components (12,14) and a bearing (16). One of the implant components has an articulation surface (18,20) for articulation with the bearing. The other implant component has a mounting surface (26) for supporting the bearing. At least one of the first and second components includes a recess (122,124,126,128,130) and a stud (132,134,136,138,140) in the recess. The joint prosthesis also includes an extension (30,32,34,36,38) mounted on the stud and extending out from the bone-engaging surface to an end (40,42,44,46,48). Part of the extension is received in the recess.
