Refinements in anesthetic and surgical techniques, implant design and application, and perioperative management have helped substantially improve treatment of complex fractures and other skeletal defects caused by trauma, disease, developmental deformity, and tumor resection. Nonetheless, an unfavorable wound environment caused by adverse tissue conditions, suboptimal surgical technique, or large body mass relative to fixation strength can lead to delayed healing or nonunion. Under these circumstances, some means of augmenting or accelerating bone regeneration would be desirable. A number of techniques have been used in attempts to achieve this goal, including various organic and inorganic osteoconductive and osteopromotive implants, biomechanical stimuli, electromagnetic stimuli, and numerous cellular and humoral factors. The gold standard for augmenting bone healing in humans and other animals, nonetheless, remains autogenous cancellous bone graft. More than 500,000 bone grafting procedures are performed annually in human patients in the United States, and 2.2 million are completed worldwide. 1 The number performed in companion animals, while undocumented, is also likely substantial.
Unfortunately, bone grafts have drawbacks. The additional anesthetic time or personnel needed for graft harvesting and the potential for an insufficient quantity of graft, limited access to donor sites, loss of osteogenic cells, donor site pain or hemorrhage, and failure of the donor bone are factors complicating cancellous autograft procedures. Similarly, allografts and xenografts carry the hazards of immune-mediated rejection and graft sequestration and, although unreported, the potential risk of disease transmission between donor and host. Bone banks are also costly to maintain. These factors have prompted the search for alternative bone augmentation technologies, and now cell therapy, gene therapy, and the use of bone growth and differentiation factors hold promise for clinical use. Although cell and gene therapies are not yet refined to the point of clinical application in orthopedic conditions, several recombinant BMPs are already being used clinically as alternatives or adjuncts to bone graft for treating a few well-defined clinical conditions in humans, possibly opening the way for their extralabel use in companion animals.