Discrimination of total body bone mineral density measured by dexa in vertebral osteoporosis

The assessment of bone mineral density (BMD) is the usual study to detect patients at risk for developing osteoporosis. The aim of this study was to compare the discriminative ability of total body BMD and its different subregions with the more usual measurements of BMD of the lumbar spine and femoral neck in women with osteoporotic fractures of the spine. The BMD was determined in 61 osteoporotic (at least one vertebral wedge fracture visible in the lateral X-ray film of the thoracic or lumbar spine) and 61 age-matched control women. Measurements were made by dual X-ray absortiometry (DXA) with a total body scanner. The BMD of the osteoporotic women was significantly lower at all skeletal areas compared with control (P<0.001). The diminution was less pronounced but still significant at the arms (P<0.05). The areas with the largest Z score in the osteoporotic group were antero-posterior lumbar spine (-1.78), femoral neck (-1.71), legs (-1.67), and total body (-1.59). There was no significant difference among the Z scores of the four above-mentioned measurements. The Z score of the arms (-0.79), spine (-1.12), and head (-1.29) were significantly lower than the Z score of the total body. The Z score of the pelvis was lower than the Z score of the total body but the difference only approached statistical significance (0.05> P<0.1). The Z score of the anteroposterior lumbar spine (-1.78) was compared with the Z score of the total (-1.12) lumbar (-0.93) and thoracic (-1.38) spine obtained as subregions of the total body. The best differentiation of the two populations was found by measuring the antero-posterior lumbar spine directly (P<0.01-P<0.001). In conclusion, the diagnostic differentiation of the total body BMD is similar to that of the anteroposterior lumbar spine and proximal femur measurements. In addition, the measurement of the total body BMD has a lower error and enables simultaneous evaluation of the different subregions of the skeleton as well as the body composition. The BMD of the spine as a subregion of the total body cannot replace the direct evaluation of the anteroposterior lumbar spine.