Effects of Anisotropy on the Longitudinal Wave Velocities in Bone

Ultrasonic wave properties of bone reflect elastic properties, which are closely-related to the bone strength. We have experimentally investigated the effects of anisotropic structure on the ultrasonic wave properties, focusing on the cancellous and cortical (compact) bovine bones. Both types of bone show interesting wave propagation phenomena. One is the two longitudinal waves-fast and slow waves-propagation in the cancellous bone. With the help of X-ray micro-computed tomography (CT), we have made clear the effects of anisotropic trabecular structure on the wave propagation. Wave properties of cortical bone also give us the clear information of elastic anisotropy. We can also find the nanoscopic effect of anisotropic orientation of polycrystalline Hydroxyapatite (HAp), on the longitudinal wave velocity in the cortical bone.