Fatigue of human cortical bone under axial-torsional loading

Since bone mass based measurements have demonstrated limited success in predicting age-related increase in fracture incidence, recent emphasis has been placed on quantification of bone quality. The current study reports the multiaxial failure characteristic of bone (quality) by conducting fatigue tests on human cortical bone specimens under physiologically relevant axial-torsional loading. Our results show for the first time that, compared to uniaxial tests, multiaxial fatigue tests show a four-fold reduction in the fatigue life of human cortical bone. Furthermore, the weak mode in physiologically relevant axial-torsional loading changes with age. Bones in the older group (> 50 yrs) were weaker in torsional than in axial loading and the bones in the younger donor group (< 50 yrs) were weaker in axial than torsional loading (p < 0.05).