A COMPARISON OF LATERAL VERSUS ANTERIOR-POSTERIOR SPINE DUAL-ENERGY X-RAY ABSORPTIOMETRY FOR THE DIAGNOSIS OF OSTEOPENIA

Because bone mineral density (BMD) measurements at various sites diffe r in the relative amounts of cortical and trabecular bone that they as sess, they also differ in their sensitivity for detecting osteopenia. Lateral spine dual energy x-ray absorptiometry (DXA) allows measuremen t of BMD of the vertebral bodies, which contain mainly trabecular bone , without contribution from the posterior vertebral elements, which ar e rich in cortical bone. Thus, we hypothesized that lateral spine DXA would detect osteopenia more frequently than anterior-posterior (AP) s pine DXA. To assess the ability of DXA to estimate trabecular bone mas s, we compared AP and lateral DXA spine measurements with trabecular b one measurements by quantitative computed tomography (QCT) in 58 patie nts. We then compared AP vs. lateral spine DXA measurements in 1) 300 women referred for routine bone densitometry, 2) 30 glucocorticoid-tre ated women, and 3) 44 women with vertebral compression fractures. To c ompare short term reproducibility, we performed repeat AP and lateral DXA scans in 50 women.