A surgical instrument, generally in the form of an expandable elongate conduit, for use as a distractor and/or retractor. The conduit generally includes a first elongate trough and a second elongate trough movable between an expanded state and a collapsed state wherein the second trough is nestable with the first trough. The first and second troughs may be fastened to vertebrae to facilitate distraction and/or compression of the vertebrae relative to one another.