Acceleration of Second and Fourth Metatarsal Fracture Healing with Recombinant Human Bone Morphogenetic Protein-2/Calcium Phosphate Cement in Horses MELANIE PERRIER DVM, YAN LU MD, BRETT NEMKE, MS, HIROHITO KOBAYASHI, MS, ANNA PETERSON, and MARK MARKEL DVM, PhD, Diplomate ACVS Objective—To compare the efficacy of recombinant human bone morphogenetic protein-2 (rhBMP-2)/calcium phosphate (CP) to autogenous cancellous bone graft (CBG) and to no treat- ment on bone healing, in surgically induced osteotomies and ostectomies of the accessory metatarsal bones in an equine model. Study Design—Experimental. Animals—Adult horses (n ¼ 9). Methods—Segmental ostectomies of the second metatarsal bone (MT2) and osteotomies of the fourth metatarsal bone (MT4) were performed bilaterally in 9 horses. There were a total of 35 defects (1 MT4 was previously fractured) created and supplemented randomly either with no treatment (untreated control), rhBMP-2/CP cement, or matrix (CPC or CPM), or CBG. Radiog- raphy was performed every 2 weeks until study endpoint at 12 weeks. After euthanasia, bone healing was evaluated using radiography, mechanical testing, and histology. Data were analyzed with ANOVA followed by the Duncan’s Multiple Range Test or nonparametric analyses. Results—At 12 weeks, radiographic scores for union were significantly greater for the rhBMP-2 (Po.0001) and CBG (P ¼ .004) groups compared with the untreated control group, for both MT2 ostectomies and MT4 osteotomies. The rhBMP-2 treated MT2 had greater maximum torque to failure in torsion than CBG and control limbs at 12 weeks (P ¼ .011). Histologic analysis demonstrated increased bone formation and more mature bone at the ostectomy site for MT2 in the rhBMP-2 and CBG groups compared with the untreated control group. Conclusion—Injection of rhBMP-2/CP into surgically induced ostectomies and osteotomies of the accessory metatarsal bones might accelerate early bone healing in the horse. Clinical Relevance—RhBMP-2/CP may be as effective if not superior to CBG as an adjuvant treatment to accelerate healing of bone defects. r Copyright 2008 by The American College of Veterinary Surgeons INTRODUCTION F RACTURES ACCOUNT for 71% of fatal muscu- loskeletal injuries in thoroughbred racehorses. 1 Forces involved in equine fractures are generally much greater than those acting on bones in humans or smaller animal species. As a result, fracture repair of long bones in the horse is often challenging and associated with un- satisfactory outcomes, with a higher incidence for com- plications, such as fixation failure or delayed healing, than in other species. Economic pressure in the horse- racing industry demands not only optimal fixation but Supported by funds from Grayson Jockey Club Research Foundation and Wyeth Discovery Research. Address reprint requests to Yan Lu, MD, Comparative Orthopaedic Research Laboratory, School of Veterinary Medicine, 2015 Linden Drive, Madison, WI 53706. E-mail: luy@svm.vetmed.wisc.edu. Submitted August 2007; Accepted March 2008 From the Comparative Orthopaedic Research Laboratory, Departments of Surgical Sciences and Medical Sciences, School of Veterinary Medicine and the Division of Sports Medicine, Department of Orthopedics and Rehabilitation, University of Wisconsin- Madison, Madison, WI. r Copyright 2008 by The American College of Veterinary Surgeons 0161-3499/08 doi:10.1111/j.1532-950X.2008.00431.x 648 Veterinary Surgery 37:648–655, 2008