A study of mineral phase in immobilized rat femur: structure refinements by Rietveld analysis

The aim of the present work was to examine whether immobilization of a limb influences the structure of bone mineral. The mineral phase in rat femora immobilized for 2 weeks during growth was investigated. Bone mineral was subjected to powder X-ray diffraction, using a scanning method after ashing the bones at 630 degrees C. Occupancy factors of ion positions in bone hydroxyapatite (HAP) were analyzed using the Rietveld refinement method. Occupancy factors of the positions OH(-), Ca(2+), and P(-) were significantly lower in immobilized than in control bones, although the position of ions in the HAP structure did not change. Mineralization of tissue in the immobilized bones was lower than in the controls, but there was no correlation between mineralization and occupancy factors. HAP lattice constants in immobilized bones were slightly but significantly different from those in controls. We conclude that the structure of HAP synthesized in bone during temporary lack of loading differs from that of HAP growing under physiological conditions. The Rietveld refinement method proved to be useful in the estimation of the changes in bone mineral.