Bone graft alternatives in spinal fusion surgery

Autograft bone is considered the gold standard for use in spinal fusion surgery. Autograft has all three properties considered essential for successful bone grafting: osteoinduction, osteoconduction, and osteogenesis. Unfortunately, the harvest of autograft bone is associated with substantial morbidity. Bone marrow aspirate is the only other potential source of osteogenic precursor cells, but provides neither osteoconductive nor osteoinductive potential, and its current usefulness involves incorporation in a composite graft. Allograft bone is the most frequently used autograft alternative, but it suffers from significant limitations, including lack of osteogenicity and significantly decreased osteoinductance compared with autograft. The risk of infection, although small, is also a concern. Demineralized bone matrix is a popular allograft product with limited osteoinductive potential and significantly less risk of infection. However, poor regulation of this product has been a criticism, and clinical efficacy in spinal fusion requires further investigation. Ceramics are purely osteoconductive in nature and have material properties that may be too brittle for use as unprotected structural grafts. Their use as a component of composite grafts has demonstrated success in animal models and preliminary human clinical trials of spinal fusion. Recombinant growth factors, specifically the bone morphogenetic proteins 2 and 7, are currently being evaluated in clinical trials, and early results have been impressive. These products may have a role in composite grafts that may exceed the efficacy of autograft in promoting spinal fusion. Use of autologous bone grafting has long been considered the most reliable means of achieving a spinal fusion in a variety of clinical settings. Autografts provide three factors identified as important for successful graft incorporation: osteoinduction, osteoconduction, and osteogenesis. However, the supply of autograft is limited, and the process of harvesting exposes patients to added morbidity, introduces another surgical site for potential complications, and often adversely affects otherwise successful patient outcomes. The many disadvantages of autograft have led to a search for effective alternatives that match or even exceed the biologic potency of autograft while avoiding the associated morbidity. So-called “bone graft alternatives” have been one of the most popular areas of investigation during the past few years. This review presents the most recent developments, focusing primarily on the numerous osteobiologic products currently available or in the final stages of clinical testing.