Objective: To compare the microarchitecture of iliac crest trabecular bone from women treated for two to three years with alendronate versus that of women treated with placebo. Research design and methods. Three-dimensional microcomputed tomography (micro-CT; resolution 20 μm) and two-dimensional histomorphometry (resolution 5-7 μm) were used to examine trabecular bone from single transilial biopsies obtained at the completion of clinical trials. Main outcome measures: Microarchitectural variables, including bone volume, trabecular number, trabecular thickness, and trabecular spacing in specimens from alendronate- and placebo-treated women were examined. Three-dimensional images of trabecular bone from both groups were constructed from CT images. Correlations among variables and between techniques were also calculated. Results: Eighty-eight specimens were suitable for evaluation by both techniques. As measured by two-dimensional histomorphometry, bone volume fraction (as a proportion of total volume) and trabecular thickness were significantly greater in alendronate specimens, 17.1 ± 5.5% vs. 13.4 ± 5.5% (p = 0.0043) and 127 ± 29 μm vs. 109 ± 28 μm (p = 0.0090), respectively, and trabecular spacing was significantly smaller, 729 ± 227 μm vs. 862 ± 338 μm (p = 0.005). Micro-CT yielded similar findings: bone volume and trabecular number were significantly greater in alendronate specimens: 19.4 ± 6.2% vs. 16.2 ± 6.3% (p = 0.0412) and 1.46 ± 0.32 vs. 1.31 ± 0.33 per mm (p = 0.0346). Two-dimensional and micro-CT measured characteristics correlated strongly with one another, with Pearson product moment correlation coefficients ranging from 0.60 (for trabecular thickness) to 0.83 (for bone volume). Conclusions: Trabecular microarchitecture of the ilium, whether studied by two- or three-dimensional methods, is better (greater bone volume, greater trabecular thickness, decreased trabecular spacing) after alendronate treatment than after two to three years of treatment with placebo. Bone volume in a trabecular region is strongly correlated to its microarchitecture, suggesting that bone quantity predicts values for these microarchitectural endpoints.
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