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: $ vBM{D}_{min}=\frac{ aBMD}{W_{PA}^{min}} $ and $ vBM{D}_{av}=\frac{ aBMD}{W_{PA}^{av}} $ (W _PA ^min —minimal vertebral body width in postero-anterior (PA) view, W _PA ^av — average PA vertebral body width). Volumetric BMD measured by QCT (vBMD), aBMD, BMAD, vBMD_min, and vBMD_av were correlated to ultimate load and ultimate stress (P_max) to find the best predictor of vertebrae BS.

Results

The coefficients of correlation between P_max and vBMD_min, vBMD_av, 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.