P3F-2 Nonlinear Resonant Ultrasound Spectroscopy for Micro Damage Assessment in Human Bone

Abstract

It has recently been demonstrated that bone micro-damage has a strong influence on bone quality and fracture risk [Zioupos, P, 2001]. However, in vivo micro-damage has remained poorly documented due to the lack of non-invasive techniques for its assessment. The aim of this work is to develop a damage assessment technique that could be used in vivo. We are attempting to apply nonlinear dynamics to monitor and ultimately characterize bone damage in vivo. Towards that goal we have conducted a suite of experiments whereby we induce progressive damage in human bone and study the simultaneous material softening that takes place, using the nonlinear resonant ultrasound spectroscopy (NRUS) technique. The feasibility of this technique for damage characterization of bovine bone has been recently demonstrated on two samples [Muller, et al., 2005]. In our experiments, damage accumulation was progressively induced in 30 samples of human femoral diaphysis by compressional fatigue cycling in a mechanical testing device. At each damage step, the nonlinear elastic parameter reflecting the material softening as a function of wave amplitude was extracted applying resonance methods. Histological measurements and synchrotron microtomography were performed for an independent characterization of damage. The nonlinear elastic parameter was compared to mechanical parameters such as the slope of the load/displacement curve and the amount of hysteresis exhibited by this curve, known as a good marker of damage. As of the first damage steps, the nonlinear parameter increased, and seemed to be more sensitive to early damage than other biomechanical parameters like hysteresis, which started to increase later in the experiment, just before the failure of the samples. An exponential relationship was found between age and the nonlinear parameter. This study suggests the ability of NRUS to characterize early fatigue damage in human bone