A model for fatigue crack propagation and remodelling in compact bone.

The process of fatigue in bone is of interest for a number of reasons. Fatigue damage in vivo can eventually lead to stress fracture, and may also act as a stimulus for bone remodelling and adaptation. The aim of this paper is to develop a theoretical model which describes the growth of fatigue cracks, especially of microcracks. The growth behaviour of microcracks is complicated by their interactions with the surrounding microstructure. This problem has been identified by researchers working on fatigue in engineering materials. Their work can be adapted to develop an equation in which the growth rate of cracks is related to applied stress conditions and also to a microstructural parameter, d, which is defined as the spacing of barriers to crack growth. The model can be used to generate stress/life data for comparison with in vitro fatigue experiments. It can also be used to investigate two hypotheses: that microcracking stimulates repair and that the level of fatigue damage can act as a signal to initiate adaptation processes of deposition or resorption.