Age dependence of the normal/abnormal difference of bone mineral density in osteoporotic women

Bone mineral density (BMD) is the major factor in bone strength and in the risk of suffering osteoporotic fractures. The aim of this study was to examine the normal/abnormal difference for antero-posterior (AP) spine, lateral spine, proximal femur and total body BMD to assess if age influences discrimination at three different decades between 50 and 80 years of age. The BMD was determined in 61 control women and 60 osteoporotic women (at least one vertebral wedge fracture readily visible in the lateral X-rays of the thoracic or lumbar spine). Measurements were made by DEXA with a total body scanner. The BMD of the whole group of osteoporotic women was markedly lower than that of age-matched controls at all skeletal areas (P < 0.001) except at the arms where the difference was smaller (P < 0.02). The Z-score (the difference between osteoporotic patients and age-matched control divided by the intrapopulation S.D.) was similar (approximately -1.7) over the AP spine, femoral neck, Ward's triangle, total body and legs. It was significantly lower at the arms (-0.8, P < 0.001), lateral spine (-1.4, P < 0.01) and trochanter (-1.3, P < 0.001) compared with the Z-score of the AP spine. The analysis of the results by decades of age disclosed that the higher Z-score on the 6th and 7th decades corresponded to the AP lumbar spine (approximately -2.0). A high descrimination was also observed for the femoral neck, Ward's triangle and legs while the Z-score of the lateral lumbar spine, total body, trochanter and arms were significantly lower than that of the AP lumbar spine. However on the 8th decade the Z-score of the AP lumbar spine diminished to -1.2 and was only significantly higher than the Z-score of the arms (P < 0.01). The study showed that, in women 50-60 years of age--the period where the majority of studies are made for prevention of osteoporosis, none of the other skeletal areas were superior to the AP spine in discrimination for spinal osteoporosis. Proximal femur and legs densitometry gave lower but not significantly different Z-score than the AP spine, while the remaining areas were significantly inferior to AP spine in separating osteoporotic and normal women.