In order to investigate and compare the mechanical behaviour of human cancellous bone during different shear loading modes, two tests were performed to characterise human femoral cancellous bone in shear: a torsion test until failure and a shear test using a sharpened stainless steel tube. Paired cylindrical samples were core drilled from 12 human femoral heads, symmetrically with respect to the coronal plane and along the primary trabecular direction. The distal part of the sample was assigned to a torsion test and the shear test was performed on the proximal part along two perpendicular anatomical directions. Apparent densities and tissue densities were measured on both torsion and shear specimens. The mean torsion properties were shear modulus G, 289 (183) MPa, ultimate stress τtorsion, 6.1 (2.7) MPa, ultimate strain γultimate, 4.6 (1.3)%, yield stress τyield, 4.3 (1.9) MPa and yield strain γyield, 1.8 (0.3)%. Strong correlation was obtained between G and τtorsion (r′=0.853, p<0.001). These torsion properties were correlated with apparent density of torsion specimens showing, respectively: r′=0.713, p=0.005 and r′=0.671, p=0.008. Properties from the shear test were invariable with regard to the two tested directions then isotropic ultimate shear stress and isotropic elementary shear stress, which represent the mean values of the two tested directions were, respectively, τshear, 10.0 (4.5) MPa and τelem, 18.8 (6.1) MPa. Both shear stresses were correlated with apparent density of shear specimens: τshear, r′=0.564, p=0.045 and τelem, r′=0.636, p=0.024. Apparent densities for shear specimens were superior than for torsion specimens (p=0.06) and the comparison was the opposite for tissue densities (p=0.028), showing strong density gradients of cancellous bone in the femoral head. These torsion and shear tests which permit the evaluation of cancellous bone behavior under two different types of shear loading, may be performed on different human sites and the measured shear properties may be compared to structural properties of cancellous bone.
Keywords: Human; Femoral head; Cancellous bone; Shear test; Torsion test; Apparent density; Tissue density; Failure