This invention relates to arthodesis for stabilizing the spine. More specifically, the present invention is directed to an intervertebral spacer formed of a bone material and to methods of treating patients having spinal deformities. The invention provides a spinal implant assembly comprising bone-derived components. The bone-derived components can be formed into modular units that can be assembled to provide a wide variety of implant configurations. In addition, the bone-derived components can form scaffold that can withstand the shear and impact forces necessary to insert the assembled implant into a disc space between adjacent vertebrae. In preferred forms the implants define an open spacer that serves as a depot for receipt of an osteoconductive material. The ostoegenic material is preferably a moldable filler that can form a molded reinforced implant.