Stiffness in discrimination of patients with vertebral fractures.

We measured the ultrasound parameters of the heels of 49 women with vertebral fractures and 87 age-matched controls using an Achilles ultrasound device. Average broadband ultrasound attenuation (BUA), speed of sound (SOS) and Stiffness were significantly lower in fracture patients (p < 0.0001). We also estimated the ultrasound parameters of patients compared with age-matched non-fracture controls and found the mean BUA to be -1.02 SD below control values. The mean SOS was -0.97 SD and the mean Stiffness was -1.12 SD below control values. Femoral bone mineral density (BMD) at the neck, Ward's triangle and the trochanter, the total-body BMD and L2-4 BMD were measured with dual-energy X-ray absorptiometry (DXA) and found to be significantly lower in fracture patients (p < 0.0001). All correlation coefficients between ultrasound parameters and DXA measurements were > 0.5 and statistically significant (p < 0.0001). A stepwise logistic regression with presence or absence of vertebral fracture as the response variable and all ultrasound--DXA parameters as the explanatory variables indicated that the best predictor of fracture was Stiffness, with additional predictive ability provided by spine BMD. Sensitivity and specificity of all measures were determined by the areas under the receiver operating characteristic (ROC) curve, which were 0.76 +/- 0.04 for BUA, 0.77 +/- 0.04 for SOS, 0.78 +/- 0.04 for Stiffness and 0.78 +/- 0.03 for spine BMD. The areas under the ROC curves of BUA, SOS, Stiffness and spine BMD were compared and it was found that Stiffness and spine BMD were significantly better predictors of fracture than BUA and SOS. These results support many recent studies showing that ultrasound measurements of the os-calcis have diagnostic sensitivity comparable to DXA, and also demonstrated that Stiffness was a better predictor of fracture than spine BMD.