Integration of metallic endoprotheses in dog femur studied by near-infrared Fourier-transform Raman microscopy

The integration of hydroxyapatite-coated implants in dog femur was studied by near-infrared Fourier-transform Raman microscopy. Raman spectra were taken in lateral scans in step widths of 10–40 μm from the implant surface up to a distance of 320 μm into the bone tissue. The spectra were subjected to a component analysis for the quantitative determination of the protein and the inorganic components. This quantitative analysis is shown to be more reliable than conventional band fitting procedures and allows, for the first time, the quantitative distinction between the hydroxyapatite form of mature bone tissue and synthetic hydroxyapatite introduced by the implant coating. It is demonstrated that full mineralization of the ongrowing bone is not achieved after 6 months. In contrast, after a residence time of 18 months in the body, the Raman spectra reveal a complete calcification of the new bone tissue as indicated by content of biological hydroxyapatite that is the same as in mature bone tissue throughout the whole implant/bone interface. On the other hand, the content of synthetic hydroxyapatite is strongly reduced in the sample prepared after eighteen months implantation whereas for the shorter implantation time, substantial contributions of synthetic hydroxyapatite are found even at positions beyond the thickness of the implant coating. These results indicate that the coating material is actively involved in the mineralization of ongrowing bone. Possible mechanisms for the underlying transport processes in the implant/bone interface are discussed.