Discrepancies between vertebral bone density values: The least dense vertebra

Abstract Vertebral bone mineral density (BMD) measurements by DXA are considered reliable indicators of local fracture risk in the absence of radiographic deformities. The clinical evaluation of one individual vertebra presenting a BMD value significantly less than the others is attempted in this study. For a period of 30 months, BMD measurements of L1–L4 vertebrae and femoral neck (FN) were performed by DXA in 817 postmenopausal women, aged under 65 years, with a BMI less than 33 kg/m 2 . In 204 (25%) of these women (group A), the least dense vertebra (LDV) presented a BMD value lower than 92.4% from the immediate denser vertebra. The remaining 613 women comprised group B. Women with X-ray proven vertebral degenerative lesions or deformities were excluded from the study. Among the four measured vertebrae, L1 was the most frequent LDV (47%), whilst L3 was the most rare (2%). Absolute and age-adjusted BMD values of L1–L4 and FN, as well as the proportions of osteopenic or osteoporotic women, did not differ significantly between the two groups. A significant positive correlation was observed between either L1–L4 or LDV and FN BMD values in both groups, but stepwise multiple regression analysis revealed that in group A the LDV did not participate in the model explaining the variability of the FN BMD values. In group B, the least dense vertebra was the only variable participating in the respective model (adjusted- R 2  = 37.7%). It is concluded that in a significant proportion of relatively young postmenopausal women, a wide variance of BMD values exists between individual vertebral BMD values without radiographic background. L1 was the most frequent LDV and L3 the most rare. In such cases, the evaluation of the least dense vertebra seems to offer an alternative estimation of vertebral bone mass, instead of mean L1–L4.