The Role of Biologics and Bone Graft Substitutes in Spinal Fusion: Current Evidence and Future Directions

Successful spinal arthrodesis requires a biologically active environment, mechanical stability, and sufficient graft material. Autologous iliac crest bone remains the reference standard because it provides osteogenic cells, osteoinductive signals, and an osteoconductive scaffold, but harvest related pain, limited volume, and additional operative morbidity have accelerated the use of osteobiologics and bone graft substitutes. This narrative review evaluates current evidence for local autograft, allograft, demineralized bone matrix, ceramics, recombinant human bone morphogenetic protein-2, cellular bone matrices, bone marrow aspirate, peptide enhanced grafts, and emerging delivery systems. Recombinant human bone morphogenetic protein-2 has the strongest comparative evidence for improving fusion in selected lumbar procedures, although dose, containment, surgical approach, and adverse event profiles remain central concerns. Demineralized bone matrix and synthetic ceramics are useful graft extenders but generally depend on host biology or an additional osteogenic source. Cellular products and autologous cell concentrates are conceptually attractive, yet supporting studies remain heterogeneous and frequently industry associated. Product selection should therefore be individualized according to fusion risk, anatomic site, graft volume, regulatory status, cost, and the quality of clinical evidence. Future progress will depend on lower dose and spatially controlled growth factor delivery, reproducible cell characterization, comparative effectiveness trials, and value-based assessment rather than fusion rate alone.