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Although stress fractures are a common injury among physically active people, women are at two-to-four times higher risk than men. While the reasons for this difference in risk are not fully understood, bone shape or geometry and density are thought to be contributing factors.

Olivia Bruce, a PhD candidate in the Department of Biomedical Engineering, Schulich School of Engineering, and Dr. Brent Edwards, PhD, co-director of the Faculty of Kinesiology's , are working to understand how bone geometry and density affect stress-fracture risk in high-risk populations.

“We’ve known for a long time that women are at higher risk than men for stress fractures. In this work, we’re seeing how bone shape and density vary between men and women,” says Bruce. “Importantly, we’re also looking to see if those differences are actually meaningful, mechanically, for the development of stress fractures.”

To conduct her research, Bruce uses advanced medical imaging and statistical approaches to characterize how bone shape and density vary among young, active adults and between males and females. This data is then combined with computational models to determine how these variations affect stress-fracture risk. She says the in the McCaig Institute for Bone and Joint Health has been a great resource for the advanced medical imaging necessary for this work; results from the main study have been published in the journal, .

“Our first generation of models suggested that females may have an increased risk of stress fracture because of subtle differences in their tibia [shin] bone geometry when compared to males,” says Edwards. “Female tibias are a bit narrower and have a thinner cortex than males, and this results in higher bone strain (deformation) during running. A really nice moment was when we developed the second generation of models on a completely new data set of females and males, and we found the exact same geometric differences.”

Stress fractures can take a minimum of 10 weeks to heal and sometimes require surgery to repair, which can be physically, financially and psychologically detrimental. People who get stress fractures are also more likely to fracture again in the future, making injury prevention critical. Understanding how bone geometry and density affect stress-fracture risk will help researchers develop screening tools, interventions, and more personalized training programs to reduce injury risk.

Another high-risk population for this type of injury is military personnel, making such research a critical need as stress fractures alone cost the American military more than US$100 million per year in medical costs and lost training time.

“We know there is really high incidence in these populations, but we don’t fully understand why,” says Bruce. “No one, surprisingly, has dug into the mechanics as to which 3D geometric features are specifically important.”

While bone shape and density are only two pieces of a larger puzzle, understanding how they affect stress-fracture risk and the disparity in risk between men and women will help researchers develop more effective injury-prevention and treatment strategies.

A related study by the researchers has been published in the journal, .