Mechanical strength of the cement–bone interface is greater in shear than in tension

The objective of this study was to determine the relative mechanical properties of the cement–bone interface due to tensile or shear loading. Mechanical tests were performed on cement–bone specimens in tensile (n=51) or shear (n=55) test jigs under the displacement control at 1 mm/min until complete failure. Before testing, the quantity of bone interdigitated with the cement was determined and served as a covariate in the study. The apparent strength of the cement–bone interface was significantly higher (p<0.0001) for the interface when loaded in shear (2.25 MPa) when compared to tensile loading (1.35 MPa). Significantly higher energies to failure (p<0.0001) and displacement before failure (p<0.01) were also determined for the shear specimens. The post-yield softening response was not different for the two test directions. The data obtained herein suggests that cement–bone interfaces with equal amounts of tensile and shear stress would be more likely to fail under tensile loading.