A system for implantation in a patients body may comprise at least one screw configured for threaded insertion into a bone of the patient and having an exterior surface, and at least one rod configured for attaching to a said screw and having an exterior surface. Hollow spaces, passages, interstices or the like may be formed in at least one of the screw and rod and are in communication with the exterior surface of the structure and extend into the structure. A substance is positioned in at least some of the hollow spaces, passages or interstices, and the substance may have a characteristic of promoting bone growth.
