Evaluation of human recombinant bone morphogenetic protein-2-loaded tricalcium phosphate implants in rabbits' bone defects

Porous beta-tricalcium phosphate (beta TCP) has osteoconductive properties. The adsorption of human recombinant bone morphogenetic protein-2 (rhBMP-2) onto TCP could realize an osteoinductive bone substitute. We evaluated it on an animal model using dual-energy X-ray absorptiometry (DEXA) and solid- state P-31 nuclear magnetic resonance (NMR) spectroscopy. beta TCP cylinder s loaded with rhBMP-2 were implanted into rabbits' femoral condyle bone def ects, and beta TCP alone as control into the controlateral femur. We studie d two different doses of rhBMP-2 (10 and 40 mu g) on two groups of four ani mals, Evaluation consisted in radiography, histology, and histomorphometry, DEXA, and NMR spectroscopy using an original method of quantification, Wit h both doses of rhBMP-2, we observed on radiographs an increase of trabecul ar hone around implants. Histology showed resorption of the ceramic, trabec ular bone with osteoblasts and osteoid substance around the implants, and c olonization inside the porous beta TCP by new bone formed. Histomorphometry showed that the osteoid surface (OS/BS was greatest with the high dose of rhBMP-2. The difference was slight between the low dose of rhBMP-2 and cont rol. DEXA showed a dose-dependent increase of bone mineral density of rhBMP -2-loaded beta TCP vs. control. NMR spectroscopy confirmed that the amount of new bone formed in beta TCP was greater when beta TCP carried rhBMP-2, a nd increased with the dose of rhBMP-2 used. We showed that beta TCP was a g ood matrix for rhBMP-2, which gave it osteoinductive properties in an ortho topic site, in a dose-dependent manner. Thus, such composite biomaterial se ems to be of great interest in reconstructive bone surgery. Further studies are needed in clinical practice to determine optimal doses. (Bone 25:55S-5 8S; 1999) (C) 1999 by Elsevier Science Inc. All rights reserved.