Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. Biologics in Spine Arthrodesis Abhishek Kannan, BS, Shah-Nawaz M. Dodwad, MD, and Wellington K. Hsu, MD Abstract: Spine fusion is a tool used in the treatment of spine trauma, tumors, and degenerative disorders. Poor outcomes re- lated to failure of fusion, however, have directed the interests of practitioners and scientists to spinal biologics that may impact fusion at the cellular level. These biologics are used to achieve successful arthrodesis in the treatment of symptomatic deformity or instability. Historically, autologous bone grafting, including iliac crest bong graft harvesting, had represented the gold standard in spinal arthrodesis. However, due to concerns over potential harvest site complications, supply limitations, and as- sociated morbidity, surgeons have turned to other bone graft options known for their osteogenic, osteoinductive, and/or os- teoconductive properties. Current bone graft selection includes autograft, allograft, demineralized bone matrix, ceramics, mes- enchymal stem cells, and recombinant human bone morphoge- netic protein. Each pose their respective advantages and disadvantages and are the focus of ongoing research investigating the safety and efficacy of their use in the setting of spinal fusion. Rh-BMP2 has been plagued by issues of widespread off-label use, controversial indications, and a wide range of adverse effects. The risks associated with high concentrations of exogenous growth factors have led to investigational efforts into nanotechnology and its application in spinal arthrodesis through the binding of endogenous growth factors. Bone graft selection remains critical to successful fusion and favorable patient outcomes, and ortho- paedic surgeons must be educated on the utility and limitations of various biologics in the setting of spine arthrodesis. Key Words: biologics, spine arthrodesis, bone graft (J Spinal Disord Tech 2015;28:163–170) C ervical and lumbar spine arthrodesis is performed in the treatment of spine trauma, tumors, and degen- erative disorders with an estimated 200,000 fusion pro- cedures performed in the United States annually. 1 Failure of fusion, or pseudarthrosis, has been reported at rates as high as 48% in multilevel posterolateral lumbar fusions. 2 Achievement of arthrodesis is a strong predictor of out- come. This motivation has led to the consequential ex- pansion of the spinal biologics arena, bringing forth new products, research, and applications. 3 Surgeons and product manufacturers have introduced the application of various biologics, including allograft materials, ce- ramics, and growth-factor augmentation to aid in spine arthrodesis. Spinal biologics alter the existing environment by enhancing specific cellular and molecular activity. In spine surgery, these are used to help facilitate a clinical goal—achieve spine arthrodesis to resolve symptomatic instability or deformity. Biological agents contribute to spinal arthrodesis via osteoinductive, osteoconductive, and/or osteogenic mechanisms. Osteoinduction is the mechanism of stimulation of primitive, undifferentiated, and pluripotent cells to develop into a bone-forming cell lineage. Osteoconduction entails the phenomenon of bone growing on a surface. 4 Aghdasi et al 2 describe osteo- conduction as the donation of biocompatible scaffolding material that provides mechanical structure upon which new bone formation takes place. Osteogenesis character- izes the continuous contribution of established osteo- progenitor cells to participate directly in bone synthesis. Spinal biologics serve to enhance the interplay of these 3 mechanisms in an effort to improve spinal arthrodesis (Table 1). AUTOGRAFT Autologous bone grafting utilizes bone obtained from the same individual receiving the graft. Historically, iliac crest bone graft (ICBG) has been the most com- monly utilized spinal biological and represented the gold standard against which all other graft substitutes are compared. Advantages include its availability and in- herent osteogenic, osteoinductive, and osteoconductive properties. With harvested bone come osteoblasts, bony matrix, growth factors, and other cytokines. 5,6 Autologous grafts can be divided into 2 types based on structural anatomy. Cancellous grafts have greater cellular diversity and activity, whereas cortical bone has enhanced mechanical properties. 6 Corticocancellous morselized autograft offers a large trabecular surface area allowing vascular and cellular ingrowth. Although auto- graft has its biological advantages, concerns remain re- garding the graft availability in regards to its finite Received for publication March 23, 2015; accepted April 13, 2015. From the Department of Orthopaedic Surgery, Feinberg School of Medicine, Northwestern University, Chicago, IL. Wellington Hsu is a paid consultant for AONA, Bioventus, Globus Medical, Lifenet, Medtronic Sofamor Danek, Pioneer, Stryker, and Synthes. He is a board or committee member for the American Academy of Orthopaedic Surgeons, the Cervical Spine Research Society, the Lumbar Spine Research Society, and the North Amer- ican Spine Society. He is on the editorial board of the Journal of Spinal Disorders and Techniques. The other authors have no conflict of interest to declare. Reprints: Wellington K. Hsu, MD, Department of Orthopaedic Surgery, Feinberg School of Medicine, Northwestern University, 676 N. St. Clair St., #1350, Chicago, IL 60611 (e-mail: wkhsu@yahoo.com). Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved. NARRATIVE REVIEW J Spinal Disord Tech  Volume 28, Number 5, June 2015 www.jspinaldisorders.com | 163