Evaluation of mineralization in bFGF-adsorbed ceramic bone implants by DEXA and computerized histomorphometry

The aim of this study was to test whether treatment of hydroxyapatite (HA) implants with basic fibroblast growth factor (bFGF) enhances mineralization of these implants when placed in bone defects. This was performed by noninvasive mineral content analysis of the implanted defects and by computerized histomorphometry of representative defect sections. The implants were impregnated with 1.0 and 10.0 ng bFGF and inserted into bone defects generated in rat tibiae. The mineralization of the defects was measured non-invasively by dual energy X-ray absorptiometry (DEXA) on days 1, 9, 21 and 30 post implantation. On day 30, decalcified bone sections were prepared for histomorphometric evaluation. A digital image of the bone section was obtained and the percent osteoid area in the sections was determined using software which was developed for this rpose. On day 21, the mineralization of bone defects was bFGF dose dependent, whereas on day 30 the mineralization differences between the bFGF doses and the control were insignificant. The histomorphometric analysis revealed a distinction between osteoid formation within the implants and their periphery. In implants absorbed with 10.0 ng bFGF, most of the osteoid formation (34.3%) occurred at the periphery, while within the implants osteoid percentage was much lower (8.2%). On the other hand, implants adsorbed with 1.0 ng bFGP showed an even distribution of the osteoid in the implants (13.5%) and their periphery (12.8%). The noninvasive DEXA measurements could not distinguish between the mineralization within the implants and their periphery. However, high correlation (r = 0.891) was found between the DEXA results and the total new osteoid percent, including the implants and their periphery. These results indicate that bone ingrowth into HA implants is responsive to bFGF impregnation, and careful optimization of its dose is indicated.