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 cylinders loaded with rhBMP-2 were implanted into rabbits' femoral condyle bone defects, and beta TCP alone as control into the controlateral femur. We studied two different doses of rhBMP-2 (10 and 40 mu g) on two groups of four animals, Evaluation consisted in radiography, histology, and histomorphometry, DEXA, and NMR spectroscopy using an original method of quantification, With both doses of rhBMP-2, we observed on radiographs an increase of trabecular hone around implants. Histology showed resorption of the ceramic, trabecular bone with osteoblasts and osteoid substance around the implants, and colonization 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 control. 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, and increased with the dose of rhBMP-2 used. We showed that beta TCP was a good matrix for rhBMP-2, which gave it osteoinductive properties in an orthotopic site, in a dose-dependent manner. Thus, such composite biomaterial seems to be of great interest in reconstructive bone surgery. Further studies are needed in clinical practice to determine optimal doses. (Bone 25:55S-58S; 1999) (C) 1999 by Elsevier Science Inc. All rights reserved.