Spectroscopically determined collagen Pyr/deH-DHLNL cross-link ratio and crystallinity indices differ markedly in recombinant congenic mice with divergent calculated bone tissue strength

Whole bone strength can be partitioned into structural and material components. In three-point bending tests of 6-month-old female humeri from the HcB/Dem recombinant congenic series, strains HcB/8 and HcB/23 differed markedly in calculated failure stress but not ash percentage. Fourier transform infrared spectroscopic imaging was used to determine whether differences in the ratio of pyridinoline (pyr; nonreducible) to dehydrodihydroxynorleucine (de-DHLNL; reducible) collagen cross-links (XLR), mineral crystallinity, or spatial ordering could account for the strains' differing biomechanical performance. HcB/8 had significantly higher XLR and significantly higher crystallinity than HcB/23. XLR and crystallinity were highly and similarly correlated in both strains. There were no significant differences between the strains' one-dimensional spatial correlation functions, suggesting no difference in short-range order between them. The strong correlation between XLR and crystallinity reflects the interdependence of the protein and mineral elements of bone. The data illustrate the importance of material properties in addition to mineral quantity to bone tissue strength.