Finite element simulation of the fatigue behaviour of cancellous bone

Fatigue failure of bone has been implicated in a number of clinical failure scenarios. At the material level, the fatigue behaviour of cancellous bone is poorly understood. At the continuum level, the fatigue behaviour of cortical and cancellous bone are similar, exhibiting material degradation during a fatigue test. Using a combined continuum damage mechanics and finite element approach, two key questions were addressed: (i) What purpose does material degradation serve in vivo? (ii) Can the fatigue behaviour of cancellous bone be predicted by applying cortical bone data at the trabecular tissue level? Material degradation significantly increases the life of a sample, by reducing the peak stresses and redistributing the load to the surrounding tissue. The application of cortical bone data to trabecular tissue appears to give reasonable estimates of the fatigue life of cancellous bone. Modulus degradation appears to be a result of trabecular fracture rather than as a result of tissue level material degradation. At present, the models only predict permanent strains of approximately 10% of the initial applied strains, as compared to the 100-200% reported in experimental studies.