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Since compact bone is demonstrably anisotropic and inhomogeneous, the measured quantities yield a plesio-velocity rather than a true sonic velocity, which makes it difficult to compare velocity measurements among several bone samples. Distribution of the plesio-velocity for 11 pairs of 2 mm thick specimens from a single mature bovine compact bone sample using 100-ns well-damped sonic pulses emitted by a 10-mHz transducer show that anisotropy exists in both axial and transverse directions and must be associated with the local structure and composition. Changes in the same specimens when wet, dry, and rehydrated show an increase in velocity and anisotropy of the dry over the wet state. The plesio-velocity is greater in the axial direction, along the bone axis, than in the transverse plane. The change in plesio-velocity from wet to dry bone is greatest along the bone axis and least in the transverse plane. Changes in dimension, when the bone specimens were dried, show the bone sample to be anisotropic in this parameter also, but in the reverse order from that for the plesio-velocity. Shrinkage is least along the osteons and a maximum in the transverse plane.

Dimensional stability of a demineralized bovine cortical bone sample was found in all media whether EDTA, saline or ethanol and water solutions or even 100% ethanol. A 6% volume shrinkage was observed, in strong contrast to the reported swelling for tail tendon fiber collagen. Sonic velocity was strongly dependent on the state and the medium, varying by a factor greater than 2. The medium appears to contribute strongly to the observed velocity suggesting that the Reuss formalism is applicable with the solid collagen skeleton as one component and the liquid in the pores as the second. Sonic anisotropy was noted although the intensity varied. The radial to axial velocity was greatest (0.93) in saline and least in 100% ethanol (0.80) indicating that the rigidity of the tissue influenced the character of sonic propagation. Two sets of intermolecular linkages are inferred. One set, in common with tendon collagen, controls the elastic properties. A second set in bone collagen maintains dimensional stability.

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