Anisotropic Poissonʹs ratio and compression modulus of cortical bone determined by speckle interferometry

Youngʹs modulus and Poissonʹs ratios of 6 mm-sized cubes of equine cortical bone were measured in compression using a micro-mechanical loading device. Surface displacements were determined by electronic speckle pattern-correlation interferometry. This method allows for non-destructive testing of very small samples in water. Analyses of standard materials showed that the method is accurate and precise for determining both Youngʹs modulus and Poissonʹs ratio. Material properties were determined concurrently in three orthogonal anatomic directions (axial, radial and transverse). Youngʹs modulus values were found to be anisotropic and consistent with values of equine cortical bone reported in the literature. Poissonʹs ratios were also found to be anisotropic, but lower than those previously reported. Poissonʹs ratios for the radial–transverse and transverse–radial directions were 0.15±0.02, for the axial–transverse and axial–radial directions 0.19±0.04, and for the transverse–axial and radial–axial direction 0.09±0.02 (mean±SD). Cubes located only millimetres apart had significantly different elastic properties, showing that significant spatial variation occurs in equine cortical bone.