Hydroxylapatite lattice preferred orientation in bone: a study of macaque, human and bovine samples

Hydroxylpatite crystallites in lamellar bone show preferred orientation. In this study, the texture (lattice preferred orientation) of the crystallites in cortical bone samples has been studied by means of synchrotron hard X-ray diffraction, performing a combined analysis with the Rietveld method to quantify fully the preferred orientation features and to obtain lattice and microstructural parameters (such as crystallite size) simultaneously. The samples were ribs from four adult female macaques of different ages, and two femurs chosen for comparison, one from a human child and one from an adult cow. The effect of the preferred orientation of the mineral component on the elastic properties is also briefly discussed. All six samples, averaging volumes of ∼0.5 mm³, show strong preferred orientation, with the hydroxylapatite c axis parallel to the bone axis. The symmetry of the texture is almost perfectly axial and clearly displays a uniform girdle of the a axis perpendicular to the bone axis. The texture strength is very similar for the four macaque rib samples, while some variation is observed in the human (weaker) and bovine (stronger) femurs. The crystallite size (8 × 30 nm) and unit-cell lattice parameters are similar in all samples. The Rietveld analysis provides for the first time a quantitative texture analysis combined with structural and microstructural hydroxylapatite analysis of the same bone samples.