Ultrasonic measurement of the calcaneus: investigation of some error sources, and correlation with femoral strength

Ultrasonic signal velocity, phase velocity and broadband ultrasonic attenuation (BUA) have been measured in 64 calcanae in vitro. Femoral strength (FS) was determined for specimens from the same cadavers in a mechanical test simulating a fall. Femoral bone mineral density (BMD) was measured using X-ray absorptiometry. Signal velocities were highly technique-dependent, and were significantly greater than phase velocities. Negative dispersion was observed. In a subset (n=23) of the calcanae, there were highly significant reductions in velocity and BUA when the cortical shell was removed. BMD was the best predictor of FS (r²=0.88). The best ultrasonic predictor was BUA (r²=0.47). Multiple regression analysis indicated that ultrasonic parameters did not significantly improve the ability of BMD to predict FS. The results suggest that ultrasound has only a limited ability to predict hip fracture strength. However, investigation of error sources and new measurement techniques can be expected to lead to improvements in the clinical performance of bone ultrasound, as well as advancing one´s understanding of the underlying interaction between bone and ultrasound