Combining areal DXA bone mineral density and vertebrae postero-anterior width improves the prediction of vertebral strength

Objective - Areal bone mineral density (aBMD) measured by dual-energy X-ray absorptiometry (DXA) is an important determinant of bone strength (BS), despite the fact that the correlation between aBMD and BS is relatively weak. Parameters that describe BS more accurately are desired. The aim of this study was to determine whether the geometrical corrections applied to aBMD would improve its ability for BS prediction. We considered new parameters, estimated from a single DXA measurement, as well as BMAD (bone mineral apparent density) reported in the literature. Materials and methods - In vitro studies were performed with the L3 vertebrae from 20 cadavers, which were studied with DXA and quantitative computed tomography (QCT). A mechanical strength assessment was carried out. Two new parameters were introduced: vBMD_{min}=\frac{aBMD}{W_{PA}^{min}} and vBMD_{av}=\frac{aBMD}{W_{PA}^{av}} \left ( W^{min}_{PA}-minimal vertebral body width in postero-anterior \left ( PA \right ) view, {W_{PA}}^{av} — average PA vertebral body width\right ). Volumetric BMD measured by QCT (vBMD), aBMD, BMAD, vBMD _{min}, and vBMD_{av} were correlated to ultimate load and ultimate stress \left ( P_{max} \right ) to find the best predictor of vertebrae BS. Results - The coefficients of correlation between P_{max} and vBDM_{min} as well as BMAD, were r = 0.626 (p = 0.005), r = 0.610 (p = 0.006) and r = 0.567 (p = 0.012), respectively. Coefficients for vBMD and aBMD are r = 0.648 (p = 0.003) and r = 0.511 (p = 0.03), respectively. Conclusions. Our results showed that aBMD normalized by vertebrae dimensions describes vertebrae BS better than aBMD alone. The considered indices vBMD_{av}, vBMD_{min} and BMAD can be measured in routine PA DXA and considerably improve BS variability prediction. vBMD_{min} is superior compared to vBMD_{av} and BMAD.