A bone milling instrument is disclosed for creating a shaped cavity from an initial cavity in a bone, the bone milling instrument comprising a reference frame, a centering member at the distal end of the reference frame, a registration surface for engaging a portion of the initial cavity, and an attachment site provided proximally of the registration surface, a guidance support member, an attachment mechanism at the first end of the guidance support member, and a constrained pathway extending between the ends of the guidance support member; a shuttle having a first connection element configured for positionably attaching the shuttle to the guidance support member, and a second connection element configured to provide a rotational coupler; and a cutting device having a cutting portion configured at a distal end thereof, and an attachment portion provided at a proximal end.