Effect of estrogen and calcitonin on vertebral bone density and vertebral height in osteoporotic women

Estrogen and calcitonin increase bone density of osteoporotic women, particularly on the axial skeleton. To verify whether the effect of these drugs might in part be biased by spurious increases in bone density due to radiologically irrelevant microfractures, and consequent subtle decreases in vertebral height, we followed the changes in vertebral bone density (VBD), assessed by quantitative computed tomography, in relation to vertebral height (VH) in 60 osteoporotic women. VH was measured as the sum of anterior, central and posterior heights of L1-L3 vertebral bodies on lateral radiographs. Patients received either salmon calcitonin (sCT: 50 IU subcutaneously three times per week, n=18), hormonal replacement therapy (HRT: conjugated estrogen 0.625 mg/day, days 1-25, plus medroxyprogesterone acetate 10 mg/day, days 16-25 of each month;n=21) or calcium alone (Ca: 1000 mg/day, n=21). After 1 year, VBD increased in the HRT group (+5.0 ± 1.9%, p=0.010), did not change significantly in the sCT group (+3.3 ± 2.3%, p=0.167), and decreased by 6.1 ± 1.0% (p<0.001) in the Ca group. By analysis of variance, the changes induced by HRT and sCT were significantly different from those observed in the Ca group (F=7.982, p<0.001). VH decreased slightly in all three subsets of patients (-0.9 ± 0.5% in sCT, -1.5 ± 0.3% in HRT, -0.1 ± 0.5% in Ca), but these changes were not significantly different between groups (F=2.545, p=0.081). Correcting for this height decrease by analysis of covariance did not affect the significant effect of sCT and HRT on VBD, compared with that of Ca (F=6.801, p=0.001). Furthermore, no correlation was found between changes in bone VBD and VH in any of the groups. These data indicate that microfractures do not significantly account for the increases in bone density during active treatment of osteoporosis with either estrogen or calcitonin.