Comparison of quantitative ultrasound in the human calcaneus with mechanical failure loads of the hip and spine

Objective Quantitative ultrasound of the calcaneus is used clinically for evaluating bone fracture risk, but its association with the mechanical properties at other skeletal sites is not well characterized. The objective was therefore to determine its predictive ability of the mechanical failure loads of the proximal femur and lumbar spine. Method In 45 human cadavers (29 males and 16 females, aged 82.5 +/- 9.6 years), we determined the speed of sound, broadband ultrasonic attenuation (BUA) and the empirical stiffness index, using a commercial quantitative ultrasound scanner. The proximal femora and the fourth vertebral body were excised and loaded to failure in a testing machine. Results Femoral failure loads ranged from 933 to 7000 N and those of the vertebrae from 1000 to 7867 N, their correlation being 0.51 in females and -0.08 in males. Forty, percent of the variability of femoral, but only 24% of the variability of the vertebral fracture loads could be predicted with calcaneal speed of sound. In the femur, a combination of speed of sound and BUA improved the prediction (r(2) = 50-60%), but not in the spine. Conclusions The study provides experimental evidence that calcaneal quantitative ultrasound is capable of predicting mechanical failure at other skeletal sites and has potential to identify patients at risk from osteoporotic fracture. The different association of quantitative ultrasound with femoral and vertebral failure may result from the influence of the cortical bone and a higher microstructure-related similarity of the calcaneus and the femur.