Effects of boundary conditions on the two wave phenomenon in cancellous bone

After the successful observation of two wave phenomenon in cancellous bone, wave characteristics have been investigated by in vitro studies. However, there still exists strong necessity to understand the effects of bone boundary conditions on the phenomenon, because the cancellous bone is always covered by a cortical layer in vivo. This paper is dedicated to the experimental and simulation studies of the effects on the two wave phenomenon. A sample of cancellous bone (76.1x45.2x12.9 mm3) and two cortical plates (thickness: 1.2 and 1.9mm) were obtained from the left radius of a racehorse. Longitudinal pulse waves around 1MHz were measured by a conventional ultrasonic pulse technique using PVDF transducers. With 3-D CT image of the sample, wave propagation was also investigated by a 3-D elastic FDTD method. We then compared wave propagation in the sample covered with cortical layers or not. In both experimental and simulation approaches, two wave phenomenon was observed in the covered sample. However, the slow wave amplitude was very sensitive to the interface conditions between the cancellous bone and cortical layers. In addition, the waves often became small due to the conditions, telling the importance of sensitive wave observation in some cases.