AGE-CHANGES OF SPINE DENSITY IN POSTERIOR-ANTERIOR AND LATERAL PROJECTIONS IN NORMAL WOMEN

Bone mineral density (BMD) was measured in 353 healthy white women usi ng dual-energy X-ray absorptiometry (DXA). Measurements were made of b oth the posterior-anterior (PA) and lateral spine, as well as the prox imal femur (neck and Ward's triangle). From age 50 to 80 years, the BM D of the PA spine and femur neck BMD had an 18% diminution (0.6%/year) , and BMD of the lateral spine showed about a 35-40% decline (1.4%/yea r). The Ward's triangle region of the femur was not quite as decreased (30% or 1.1%/year). The BMD decrease associated with aging did not di ffer as much among sites when expressed relative to the intrapopulatio n variation rather than as a percentage. The Z-score for PA spine and femur neck BMD (- 1.1) was significantly different than that for later al spine BMD (-1.6); Ward's triangle was intermediate (-1.3), i.e., th e lateral spine still showed the highest sensitivity to aging. However , the ability to detect age changes in an individual subject can be in creased only if the precision error for lateral spine BMD is not incre ased to a greater extent than the sensitivity.