Comparison of histomorphometric descriptors of bone architecture with dual-energy X-ray absorptiometry for assessing bone loss in the orchidectomized rat.

We have compared different methods for measuring bone loss in the orchidectomized (ORX) rat model of male osteoporosis: densitometry (DXA), ash weight, anatomic bone indices, histomorphometry and two-dimensional trabecular architecture analysis. Forty-eight male Wistar rats were studied at 2, 4, 8 and 16 weeks (four groups). In each group, 6 rats were ORX and 6 sham-operated were used as control. DXA was performed on the whole body, tibia and femur. Histomorphometry was performed on the secondary spongiosa of the tibia: trabecular bone volume (BV/TV) and trabecular characteristics (number, separation and thickness) were measured. Architecture analysis comprised strut identification, star volume of the marrow spaces and trabeculae, Euler-Poincaré number (E) and Kolmogorov fractal dimension (Dk). Bone mineral densities of the whole body, tibia and femur were reduced at 16 weeks in the ORX group. BV/TV was significantly decreased in the ORX group from the fourth week. Differences in the sensitivity of the architectural methods were found. There were no differences in trabecular thickness nor in trabecular star volume between ORX and controls even after 16 weeks. E became different at 8 weeks. Trabecular number, node count, star volume of the marrow spaces and trabecular separation became significantly different at 4 weeks Dk was modified after 2 weeks (p < 0.05 at 2 weeks, p < 0.001 from 4 weeks). In the ORX model, Dk appeared the most potent descriptor of trabecular bone disorganization by revealing the earliest changes at the network level.