Open chambered spacers, implanting tools and methods are provided. The spacers 500' include a body 505' having a wall 506' which defines a chamber 530' and an opening 531' in communication with the chamber 530'. In one embodiment the wall 506' includes a pair of arms 520', 521' facing one another and forming a mouth 525' to the chamber 530'. Preferably, one of the arms 520' is truncated relative to the other, forming a channel 526. In one aspect the body 505' is a bone dowel comprising an off-center plug from the diaphysis of a long bone. The tools 800 include spacer engaging means for engaging a spacer and occlusion means for blocking an opening defined in the spacer. In some embodiments, the occlusion means 820 includes a plate 821 extendable from the housing 805. In one specific embodiment the plate 821 defines a groove 822 which is disposed around a fastener 830 attached to the housing 805 so that the plate 821 is slideable relative to the housing 805.