A device for holding in compression, a bone graft placed in the space between two vertebral bodies and from which a diseased or injured vertebral body has been removed, comprises an elongate space-spanning plate of implant grade material having a concavo-convex cross section, with an integral prong at each end to be driven into the vertebral bodies. Each prong has a proximal portion and a distal portion, with each portion having an inboard surface facing an inboard surface of the other prong, the inboard surfaces converging as they extend from the distal ends of the prongs toward the concave surface of the plate to urge the vertebral bodies toward each other as the prongs are driven into them. The outboard surface at the proximal portion of the prong is parallel to the inboard surface and at the distal portion converges from the proximal portion to intersection with the inboard surface at the distal end of the prong. The plate has two holes in it adjacent each end for reception of bone screws but which are used during installation of the staple for reception of the locating posts of an impactor tool to properly position the tool for striking it with a mallet to drive the staple prongs into the vertebra. Consequently, as the staple is installed by striking the impactor, the prongs enter and become embedded and are anchored in the vertebral bodies adjacent the graft and urge the bodies toward each other, placing the graft under compression. Then bone screws are installed through the plate into the vertebral bodies to permanently anchor the plate and immobilize the two vertebral bodies relative to each other.