An implant assembly having an articulating surface and an axial cavity arranged to receive an end of a bone, the axial cavity being generally circular in cross section in a plane normal to the axis of the implant, and including a spacing element detachable from the implant. At least a portion of the interior surface of the cavity is roughened and is arranged to abrade bone when the end of the bone is received in the cavity. The spacing element is arranged to prevent the implant from fully seating on the end of the bone such that the implant and the end of the bone are in a predetermined spaced apart arrangement.
