[Dual-energy X-ray absorptiometry of the vertebrae: determining which vertebrae should be scanned]

This study was aimed at verifying whether bone mineral density (BMD) and its loss with aging are different in the lumbar vertebrae and whether the region of interest--which is usually limited to the L2-L4 segment--may be extended to L1-L4. BMD was measured by means of dual-energy X-ray absorptiometry (Hologic QDR 1000) in 74 women, aged 37 to 78 years, not affected with any disease or subjected to any treatment known to interfere with bone metabolism. The relationship between age and BMD was expressed by the following equations for L1, L2, L3: BMD-L1 = 1181.68-7.85 x age, BDM-L2 = 1251.57-7.70 x age, BMD-L3 = 1231.66-6.57 x age, as shown by linear regression analysis. The behavior of the bone density of L4 with age appeared to be different and could not be described by linear regression curves and was therefore not comparable with that of the other vertebrae. BMD was different in the four lumbar vertebrae as shown by: a) the diversity of the intercept of the regression lines describing age-bone density relationships (F = 7.7, p < 0.001); b) the bone density of L1 being lower than the mean bone density of the L2-L4 region (p < 0.005); c) the bone density of L4 being higher than the mean bone density of the L1-L3 region (p < 0.001). In order to evaluate the effect of senile degenerative changes of the vertebrae on the relevant bone density, two groups of women were considered, according to age--i.e., pre- or iuxtamenopausal and late postmenopausal. It appeared that the BMD of L1 was always more correlated to the bone density of L2 and L3 than the BMD of L4. Our results suggest that L1 is homogeneous to the L2-L3 region, relative to both bone density and its loss with aging. Therefore, L1 should be included in the region of interest during the examination. Even though the bone mineral content of L4 and its loss with aging seem to be different, our results do not allow the exclusion of L4 from the scanned area.