Yield Behavior of Bovine Cancellous Bone

The compressive yield strain was measured for 61 specimens of bovine cancellous bone from three distal femora. There was no significant relationship (p = 0.08, R² = 0.051) between yield strain and the degree of trabecular orientation. There was a significant positive correlation (p<0.00001, R² = 0.319) between yield strain and structural (apparent) density and significant negative correlation (p<0.0025, R² = 0.145) between yield strain and bone density. Yield strain correlated best with bone solid volume fraction V_v (ε_y = 0.592 + 1.446v_v, R² = 0.337). The quantity, yield strain, is highly dependent on specific definitions of the yield point and the point of zero strain. For this study the yield point was defined by a 0.0003 offset criterion, and the point of zero strain was defined as the point where the tangent at 15 percent of yield crosses zero. The results using these definitions were compared with results using yield strain values determined by other definitions of the yield point and zero strain. The correlations between yield strain and trabecular orientation, structural density and bone density changed very little for differing definitions of yield. The results suggest that yield strain in cancellous bone is isotropic or independent of textural anisotropy, so the yield behavior may be characterized by a maximum strain yield criterion. The results also suggest that the primary mode of yield in cancellous bone is buckling of the trabeculae.