A flexible-shaft surgical instrument has a compression member that is distally movable to provide a compression force between the compression member and a distal compression bearing to compress a plurality of links and rigidly lock a semi-rigid tube formed by those links at any of a variety of user-selectable predetermined positions. The semi-rigid tube is configured to be bent and locked at the user-selectable predetermined position and, upon proximal movement of the compression member, returned to an unlocked state without significant plastic deformation of the semi-rigid tube.
