Histomorphometrical analysis of the bone-implant interface: comparison of microradiography and brightfield microscopy

Section thickness has been shown to affect the histomorphometrical measurement of bone-implant contact when analysed under brightfield microscopy. This study investigated whether microradiography of the bone-implant interface eliminated the errors associated with thick section analysis. Seven implant containing sections were utilized. Microadiographs of the thick (approximately 100 microns) sections were taken and the sections were subsequently ground to thicknesses of 50 microns and 25 microns. Photomicrographs were taken of the microradiographs and of the sections at each thickness (100, 50 and 25 microns) under brightfield microscopy. The photomicrographs were analysed for direct bone-implant contact in the cortical passage region and along the total length of the implant. The effect of section thickness on multiple fluorochrome labelling in 10 rabbit femur specimens was also examined. Centre-to-centre interlabel distance was measured for each label pair at a thickness of 100 microns and then again after the sections were ground to 50 microns and 25 microns. The thick (100 microns) sections showed a significantly greater amount of bone-implant contact than either the thin sections or the microradiographs. There was no difference in direct bone-implant contact measured by microradiography or thin sections. However, the microradiographic analysis showed a much lower variability of the bone-implant contact than the sections evaluated under brightfield microscopy. In addition, they have the added benefit of providing information on bone mineral density. Centre-to-centre interlabel distance was not significantly different for any label pair owing to section thickness. Data from this study provides evidence that the use of microradiographs for histomorphometrical analysis of the bone-implant interface is superior to brightfield analysis of thin sections owing to the lower variability of microradiographical data and the ability to obtain bone mineral density measures. Additionally, given that interlabel distance was not significantly affected by section thickness, the use of 100 microns thick sections for analysis of fluorochrome labels in cortical bone is supported.