Inhomogeneities in anisotropic elastic constants of cortical bone

Two different acoustic techniques were used to investigate inhomogeneity patterns in anisotropic elastic constants of the human tibia and femur using a standard transmission method, to investigate the entire cross section of the same cortical bones using a low-frequency acoustic microscope and to correlate the acoustic impedance values obtained with this microscope with the c33 (longitudinal direction) found in transmission. Eighty femoral and 120 tibial specimens prepared from 20 pairs of femur and tibia obtained via autopsy were investigated. The longitudinal elastic stiffness was significantly higher in the tibia compared to the femur, while all other elastic constants were identical. The elastic stiffness patterns were completely different for the two bones and in good agreement with the average acoustic impedance found with the acoustic microscope in the same anatomical locations