Separate assessment of forearm cortical and trabecular bone density from standard densitometry data

BACKGROUND. Cortical and trabecular bone are different bone components. The ir mineral density cannot be measured directly by areal bone densitometry. AIM. To introduce a method for assessment of pure radial cortical and trabe cular bone density based on standard densitometry data. METHOD. The study included 418 healthy females (aged 20-83 years, body mass index between 19 and 30) free of previous fractures and conditions or drug s affecting bone metabolism; as well as a group of 64 age-matched females w ith early menopause. Forearm bone density was measured by single X-ray abso rptiometry and calculated separately for cortical and trabecular bone. Age- adjusted bone density curves were built. RESULTS. Peak bone density was found to occur between 30 and 34 years of ag e and was 0.561 g/cm(2) for cortical and 0.281 g/cm(2) for trabecular bone. In comparison, lowest values were registered between 70 and 74 years of ag e, cortical bone density reduced by 26% and trabecular density by 44%. Both bone density profiles through life reflected the earlier peri- and postmen opausal (mainly trabecular) and later senile (cortical bone also involved) changes in bone mass. A step-wise pattern of trabecular bone reduction was registered with acceleration around 45, 55 and 65 years. The effects of ear ly menopause on trabecular and cortical bone were tested in the prematurely menopausal women. CONCLUSIONS. The ability of our model to discriminate between natural and p remature menopause was moderate. Although hypothetical (based on calculatio ns from integral densitometry data rather than on direct measurements), our method could differentiate between cortical and trabecular osteopenia and may prove helpful in assessing the type of osteoporosis, in making therapy choices and monitoring response to therapy based on forearm bone density.