Graft Substitutes for Use in Spinal Fusions

Spinal fusion procedures remain a common therapeutic option for various pathologic conditions of the human spine. The most frequent method for inducing spinal fusion uses autologous bone grafts harvested from the iliac crest or from local bone removed during the spinal decompression. Although autologous bone remains the ¡§gold standard¡ ̈ for stimulating bone repair and regeneration, modern molecular biology and bioengineering techniques have produced unique materials that have potent osteoconductive or osteoinductive activities. Recombinant human osteogenic growth factors, such as bone morphogenetic proteins (BMPs), transforming growth factor -ƒÒ (TGF-ƒÒ), and platelet-derived growth factor (PDGF), can now be produced in highly concentrated and pure forms. They have now been shown to be extremely potent when delivered in vivo in rats, dogs, primates, and humans. The delivery of pluripotent genetically modified mesenchymal stem cells (MSCs) to regions requiring bone formation is also compelling and has successfully induced osteogenesis in numerous preclinical studies in rats and dogs. Finally, the identification of biologic and nonbiologic scaffolding materials is an extremely important component of future bone graft substitutes, not only as a delivery vehicle for bone growth factors and MSCs, but also as an osteoconductive matrix to directly stimulate bone deposition. In this paper, we will review the currently available bone graft substitutes, in addition to novel molecular approaches, that are currently being developed for use in the clinical setting.