ELASTIC-WAVE PROPAGATION IN BONE IN-VIVO - METHODOLOGY

The purpose of this study was to investigate the usefulness of elastic wave propagation (EWP) in estimating the mechanical properties (elast icity) of human tibia. The test group was composed of 78-yr-old women assigned to high (n = 19) and low (n = 17) bone mineral density (BMD) groups as measured at the calcaneus by the I-125-photon absorption met hod. The EWP apparatus consisted of an impact-producing hammer with a force strain gauge and two accelerometers positioned on the bone. Resu lts for nylon and acrylic were used to calibrate the apparatus. Polyvi nyl chloride (PVC) solid rods and tubes of various diameters were used to evaluate the relationship between the elastic wave velocity and cr oss-sectional area. The density and the cross-sectional area of tibia were measured by the computerized tomographic (CT) method at the same intersection points as velocity recordings. The velocities in tibia of bending waves produced by the mechanical hammer were found to depend on the density, area moment of inertia, and density-dependent elastic constants of bone. It is important to account for the changes of these quantities along the bone. It is suggested that the velocity of elast ic waves and various indices derived there from provide inexpensive wa ys of evaluating the elastic properties of bone.