Figure 5.

Etiological model of stress fracture with competition between a pathological loop on the left and a protective loop on the right. With loading, the strains generated may result in a cycle of microdamage generation and targeted bone remodeling which includes osteoclastic bone resorption. Resorption can lead to temporary porosity, decreased bone stiffness and further microdamage generation. Porosity is only temporary, as coupled bone formation will eventually restore stiffness. However, this process requires up to a year for completion (see Figure 1(d) to (g)). Without appropriate rest, this cycle may lead to stress fracture, and is therefore considered pathophysiological. The same strains that initiate microdamage formation concurrently stimulate adaptive bone formation which increases bone stiffness, thereby preventing increases in strain with continued loading. This protective loop of adaptive bone formation has the potential to offset the pathophysiological loop and prevent stress fracture. (A color version of this figure is available in the online journal.)