An adapter to provide moveable configurations of securing structures such as fastener apertures or throughbores for fastening a surgical instrument to an anatomical structure, such as a bone. The adapter is connectable to the surgical instrument in a plurality of discrete locations on the surgical instrument, thereby allowing a surgeon to select an optimum fixation location for fastening the surgical instrument to the anatomical structure. The adapter may be cannulated to accommodate a fastener and may be slidably affixed to the surgical instrument while simultaneously providing stable fixation between the surgical instrument and the bone. The adapter may be configured to mate with another adapter having a similar configuration such that multiple fixation locations may be provided to the surgeon. Moreover, a plurality of adapters may be connected to the surgical instrument either directly or indirectly through another adapter to select multiple optimum fixation locations.