Composite implant composed of hydroxyapatite and bone morphogenetic protein in the healing of a canine ulnar defect

Background and Aims: Hydroxyapatite (HA) has been considered as a carrier m aterial for bone morphogenetic proteins (BMP). The aim of this study was to evaluate the capacity of a composite implant of HA and native bovine BMP t o heal a 2 cm segmental defect in the canine ulna. Materials and Methods: A composite HA+BMP implant was compared with plain H A implants and cortical autografts. The fixation was accomplished with an i ntramedullary Kirschner wire. The bone union was evaluated by X-rays taken at operation and after 3, 6, 9, 12, 16, 25, 35 weeks and by histology and m echanical torsion tests. Results: HA implants were not able to produce complete bone union even with BMP. There was some bridging between the implant and the bone in the defec ts treated with either plain HA or HA+BMP implant, the bridging being sligh tly more pronounced with HA+BMP. The autografts showed is significantly bet ter capacity to heal the defect. The HA implant did not resorb markedly dur ing the study. There was no significant difference in mechanical strength b etween the HA and HA+BMP groups. Conclusions: HA was not an adequate bone substitute material in this study model, and BMP was not able to enhance sufficiently the poor capacity of HA to heal canine ulnar defects.