Abstract: Preliminary to cementing a prosthesis in a hole in an intramedullary bone, annular groves are formed in the bone around the hole by cutters radially extensible in opposite directions from a tool driven by a cannulated rotary power unit. A control rod extends through the power unit and through a cannulated shank of the tool held by the power unit. A control unit mounted on the power unit moves the control rod lengthwise to cause projection and retraction of the cutters while rotating to groove a bone as well when not rotating.