Age- and sex-related changes in iliac cortical bone mass and remodeling

Iliac crest bone biopsies were obtained from 64 normal individuals (41 women and 23 men) aged 19-90 (mean 48.2) years. Thirty-four were double-labeled with tetracycline before biopsy. The following variables were measured in all biopsies: biopsy core width (C.Wi), absolute (A.Ct.Wi) and fractional (F.Ct.Wi) cortical width, absolute (A.Cn.Wi) and fractional (F.Cn.Wi) cancellous width, cortical porosity (Ct.Po), osteon diameter (On.Dm), Haversian canal diameter (Ha.Ca.Dm), and wall thickness (W.Th). In the tetracycline-labeled biopsies the typical cortical remodeling cycle was reconstructed and the activation frequency was estimated. A negative cortical bone balance with aging was found in both sexes. In females F.Ct.Wi decreased (p < 0.02) with aging because of marrow expansion (p < 0.05). Furthermore, Ct.Po increased (p < 0.001) because of a decrease in W.Th (p < 0.01) and an increase in H.Ca.Dm (p < 0.001). In males the negative cortical bone balance with aging was exclusively caused by an increase in Ct.Po (p < 0.001) partially explained by an expanding H.Ca.Dm (p < 0.01). The On.Dm increased with aging (p < 0.01), but surprisingly, no fall in W.Th was observed. Reconstruction of the remodeling cycle did not reveal any significant difference between younger women and men. However, the activation frequency rose from 0.5 per year in premenopausal to 1.0 per year in postmenopausal women (p < 0.001), giving rise to a high turnover state, an increase in the remodeling space, and thereby the porosity in the cortical bone immediately after menopause. The present study has shown a reduction in cortical bone mass in elderly people, compared with younger, which may be explained by an age-related remodeling imbalance. This reduction is further increased in women in the postmenopausal state because of a postmenopausal accelerated bone turnover.