Open chambered spacers, implanting tools and methods are provided. The spacers (100) include a body (105) having a wall (106) which defines a chamber (130) and an opening (131) in communication with the chamber (130). In one embodiment the wall (106) includes a pair of arms (120, 121) facing one another and forming a mouth (110) to the chamber (130). Each of the arms has an end configured to form a region within which an adjacent spacer can nest. In one aspect the body (105) is a bone dowel comprising an off-center plug from the diaphysis of a long bone. The tool (300) includes spacer engaging means for engaging a spacer and occlusion means for blocking an opening defined in the spacer. In some embodiments, the occlusion means (320) includes a plate (321) extendible from the housing (305). In one specific embodiment the plate (321) defines a groove (322) which is disposed around a fastener (330) attached to the housing (305) so that the plate (321) is slideable relative to the housing (305).
