ANTEROPOSTERIOR VERSUS LATERAL BONE-MINERAL DENSITY OF SPINE ASSESSEDBY DUAL X-RAY ABSORPTIOMETRY

Recently, it has been suggested that lateral (LAT) spine bone mass mea surements by absorptiometry may be more sensitive for detecting bone l oss than the standard anteroposterior (AP) projection. The aim of this study was to evaluate the precision of LAT spine dual-energy X-ray ab sorptiometry (DEXA) and its diagnostic sensitivity. A group of 1554 su bjects with no risk factors that might affect bone metabolism and 185 osteoporotic patients with vertebral fractures were studied. Bone mine ral density (BMD) was measured in the lumbar spine (standard AP and LA T projections) and proximal femur with a DEXA absorptiometer. The prec ision of the measurements was assessed in 15 volunteers. Diagnostic se nsitivity was evaluated by the Z-score method. Comparing young people and the elderly, spine bone loss in the latter was similar for AP and LAT projections, when it was evaluated in absolute values (glcm(2)). H owever, when it was evaluated in percentage terms, bone loss was about twice as high in the LAT projection. LAT spine BMD correlated signifi cantly with all the other ar eas assessed. The best correlation was fo und with the standard AP projection (r=0.67, P<0.0001). The precision in the LAT projection was found to be within an acceptable range (1.6% in normal subjects, 2% in osteoporotic patients), even though it was about twice that obtained in the AP projection. Diagnostic sensitivity was also better with the AP projection. It is concluded that LAT spin e BMD measurements can be assessed with acceptable precision although it is about twice as high as for AP spine measurements. The percentage decrease in BMD in the elderly is greater for measurements made in th e LAT projection than for measurements made in the AP projection. Howe ver, there is no enhancement of diagnostic sensitivity in osteoporosis . BMD measurements in the LAT projection are not as good as in the AP projection but they may offer complementary information of the regiona l evolution of spine bone mass.