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 energ y X-ray absorptiometry (DXA), histomorphometry, ash weight, and two morphom etric indices (robusticity and bone weight/bone length index) in the orchid ectomized (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 mug/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. B one volumes (C.BV/C.TV, and BV/TV) were measured by histomorphometry on the proximal tibial. A significant correlation was obtained between weight mea sured by DXA and scale (r = 0.993, P < 0.000001), However, DXA underestimat ed 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 as h weight were highly correlated (r = 0.992, P < 0.000001). However, DXA ove restimated BMC by 11% and the overestimation was found to be clearly depend ent on the net mineral content of the bone.