In vivo assessment of bone mechanical properties by vibration and ultrasonic wave propagation analysis

Vibration analysis and ultrasonic wave propagation analysis were evaluated as noninvasive techniques for the in vivo assessment of bone mechanical properties. The relation between the resonant frequencies, obtained by vibration analysis, and geometrical and material properties of long bones is explained using a simple beam model. This simple beam model was validated experimentally in previous work on excised animal bones. In vitro measurements were performed on human and animal excised bones from specific osteopenic cases and control groups. Using specific protocols for in vivo vibration and ultrasound measurements of the tibia, a population of osteoporotic patients and age-matched controls were tested. From these measurements, it was concluded that the bending rigidity, calculated from the resonant frequencies, in osteoporotic tibiae had decreased as compared to the control group. Also the ultrasound velocity in the tibial cortex was lower in the osteoporotic group. The latter indicates a change in the bone tissue material properties. On the other hand, immobilization osteoporosis appeared to lead to a decrease in bending rigidity without an observable change in bone tissue material properties. By the combination of vibration analysis and ultrasound velocity measurements, the whole bone's mechanical characteristics as well as the bone tissue properties can be assessed in vivo. Since both techniques are noninvasive, they can be used in longitudinal studies for the assessment of bone response on physical loading.