No augmentation of morselized and impacted bone graft by OP-1 in a weight-bearing model

INTRODUCTION: Impacted morselized bone allograft is thought to be remodeled to a great extent. We have previously shown that load-bearing increases the remodeling of impacted morselized bone allografts in a rabbit knee prosthesis model. Bone Morphogenic Proteins (BMPs) also stimulate bone formation and bone allograft remodeling. In this study, our aim was to determine whether it was possible to increase further the remodeling of impacted morselized bone allografts by combining load-bearing with a BMP. EXPERIMENT: A solution of Osteogenic Protein-1 (OP-1, also called BMP-7) was added to freeze-dried bone allograft chips before impaction grafting in our rabbit knee prosthesis model. 23 skeletally mature rabbits received an uncemented tibial knee prosthetic component inserted into a bed of impacted morselized bone allograft. 12 rabbits were given OP-1-treated allograft (50 microg OP-1 per gram allograft), and 11 rabbits vehicle-treated allograft. Each rabbit received mean 0.53 g graft. The rabbits were killed after 3 or 6 weeks and the grafted region was examined by histomorphometric assessment of the volume fraction of newly formed bone and remaining graft. RESULTS AND INTERPRETATION: We found that OP-1 did not increase the bone density (graft plus new bone) to any substantial extent. However, we can not exclude that this might be due to a carrier problem, since the OP-1 was added as a solution directly to the dry graft.