Improved osseointegration of titanium implants of different surface characteristics by the use of bone morphogenetic protein (BMP-3): an animal study performed at the metaphyseal bone bed in dogs

AIM: Aim of this study was to determine whether coating of titanium implants of various surfaces with BMP-3 would improve the osseous integration of the implants into the orthotopic bony implant bed. METHOD: In this experimental study 190 micro g per implant of highly purified bone morphogenetic protein 3 (BMP-3) precipitate isolated from porcine bone were available for the coating of each of 24 cylindrical test implants (12 with hydroxyapatite and 12 with plasmapore surface). The remaining 24 test implants with the same surface makeup served as negative controls. Implantation sites were randomly assigned for the 4 versions of implants available and all implants were embedded into the medial or lateral femoral condyle of both legs of 12 German shepherds. The drilling holes were performed in such a matter that after embedding the cylindrical devices a gap of 1 mm surrounding the implants remained. A biomechanical testing and histological evaluation was performed on the explants 42 days after surgery. RESULTS: In biomechanical testing forces necessary to extract the implants from the explanted bones in BMP-3 coated devices were up to 70% higher compared to the ones in the non-coated reference groups. Quantitative histomorphometric examination showed in BMP-3-coated implants an increasing formation of new bone close to their own surface (gap-healing) which was higher than in the corresponding non-coated controls (hydroxyapatite + BMP-3 32.1%, hydroxyapatite controls 20.3%, plasmapore + BMP-3 30.2%, plasmapore controls 13.1%). The extent of direct bone implant contact as percentiles of the corresponding implants perimeter (ongrowth) was also significantly higher in the BMP-3-coated implants compared to the non-coated controls (hydroxyapatite + BMP-3 37.7%, hydroxyapatite controls 22.4%, plasmapore + BMP-3 15.3%, plasmapore controls 6.4%). CONCLUSION: In this study it was proven the first time that implants of various surface textures as used in endoprosthetics are able to be coated by the osteoinductive growth factor BMP-3. In that way metallic implants can achieve osteogenic properties which have positive effects in osseointegration.