Comparison insight dual X-ray absorptiometry (DXA), histomorphometry, ash weight, and morphometric indices for bone evaluation in an animal model (the orchidectomized rat) of male osteoporosis

We have compared the measurements obtained by different methods: dual energy X-ray absorptiometry (DXA), histomorphometry, ash weight, and two morphometric indices (robusticity and bone weight/bone length index) in the orchidectomized (ORX) rat model of male osteoporosis. We examined 144 male wistar rats: 48 shamoperated, 48 ORX, and 48 ORX-treated with a bisphosphonate (risedronate) 2 or 10 µg/kg/day, 5 days per week. Rats were sacrificed at 2, 4, 8, or 16 weeks after the beginning of the study. DXA was performed on a Hologic QDR 2000 on the whole body, whole tibia, and tibial metaphysis. Bone volumes (C.BV/C.TV, and BV/TV) were measured by histomorphometry on the proximal tibial. A significant correlation was obtained between weight measured by DXA and scale (r=0.993, P <0.000001). However, DXA underestimated weight by 0.3%. This discrepancy was dependent on the rat’s weight. The weight bone length (WL) index was linearly correlated with BMD (r=0.86), BMC (r=0.96), and ash weight (r=0.97). Correlation with robusticity was lower than with the WL index. A significant correlation was found between BMC of the metaphyseal region and the bone volumes but this explained only 27% of the variance; correlation with BMD was poorer (r=0.40). BMC and ash weight were highly correlated (r=0.992, P <0.000001). However, DXA overestimated BMC by 11% and the overestimation was found to be clearly dependent on the net mineral content of the bone.