Effect of ethnicity and age or menopause on the structure and geometry of iliac bone.

We measured indices of bone volume (cancellous, cortical) and bone surface (cancellous, endocortical, and intracortical) in intact full-thickness transiliac bone biopsies obtained from 144 healthy women aged 20-74 (35 black and 109 white, 62 premenopausal and 82 postmenopausal). The data were analyzed by two-way analysis of variance of the four groups defined by age/menopause and ethnicity and by linear regression of major variables on age. None of the interaction terms was significant, and none of the regression slopes on age differed between blacks and whites, indicating that the effects of ethnicity and of age/menopause were independent. Accordingly, the data were also analyzed separately for the effects of ethnicity (pre- and postmenopausal combined) and age/menopause (blacks and whites combined). The analyses led to the following conclusions. (1) Blacks have more cancellous and cortical bone than whites in the ilium; the difference was due to thicker trabeculae and thicker cortices with no difference in trabecular number or cortical porosity. (2) The magnitude of the black/white differences was the same throughout the age range covered by the study, indicating differences in peak adult values, not in rates of loss with age. (3) As the result of age/menopause, there were significant reductions in all indices of the amount and structure of bone except for trabecular thickness; the magnitude of the reductions was the same in blacks and whites. (4) Cancellous bone loss was mainly the result of the complete removal of some trabecular elements with increased separation between remaining elements. Cortical bone loss was due to thinning from the endocortical surface with a small but significant contribution from increased cortical porosity, due to an increased number of intracortical canals. These patterns of bone loss were the same in blacks and whites. (5) Although the percentage losses of bone with age/menopause were higher for cancellous than for cortical bone, the absolute amounts of bone lost were about the same for cortical as for cancellous bone. (6) The ratio of surface to tissue volume decreased with age/menopause in cancellous bone but increased in cortical bone; rates of bone loss would change in the same manner if the loss per unit of surface remained constant. (7) The total extent of bone surface in the ilium did not change with age/menopause, so that the surface/volume ratio for the entire bone increased; volumetric bone turnover would increase and bone age decrease if remodeling activity per unit of surface remained constant.