Identification of Predictive Risk Factors for the Development of a Stress Fracture Within 6 Months in Highly Trained Female Long-Distance Runners: A Prospective Cohort Study.

Background: Female runners have a higher risk of stress fractures compared with their male counterparts. However, the literature about best practices for preventing stress fractures in female long-distance runners is lacking. Purpose: To identify which factors predict the risk of stress fractures within 6 months in highly trained female long-distance runners. Study Design: Cohort study; Level of evidence, 2. Methods: We measured bone mineral densities (whole body and lumbar spine) and body composition using dual-energy X-ray absorptiometry (DXA) in 21 highly trained female long-distance runners aged 18 to 37 years who belonged to a women's track team. Participants were followed prospectively for 6 months. Stress fractures were confirmed with bone scan, magnetic resonance imaging, and/or computed tomography findings. We employed univariate logistic regression and stepwise multivariate logistic regression, along with receiver operating characteristic curves, to examine the ability of bone mass and body composition parameters, alone or in combination, to predict the occurrence of a stress fracture. Results: We performed 118 DXA measurements. Stress fractures (4 sacral, 3 tibial, 3 calcaneal, 2 pubic, 2 femoral neck, 1 rib, 1 cuboid, and 1 metatarsal) occurred in 9 runners within 6 months. Bone mineral densities (% of young adult mean [YAM]; whole body: odds ratio [OR], 0.923; lumbar spine: OR, 0.914), total bone mineral content (BMC) (OR, 0.019), lean body mass (OR, 0.807), and percentage total BMC relative to total body mass (OR, 0.197) were significantly associated with a stress fracture developing. The multivariate analysis showed that bone mineral density of the lumbar spine alone was the strongest predictive factor (OR, 0.914 [95% CI, 0.853-0.963]). A lumbar spine bone mineral density <81.1% of the YAM predicted a stress fracture within 6 months, with 88% sensitivity and 74% specificity (area under the curve, 0.818). Conclusion: Our study demonstrated that highly trained female long-distance runners with lumbar spine bone mineral density <81.1% are at increased risk of a stress fracture within 6 months and should reduce their high-impact sports activities to avoid developing a stress fracture. The present study may provide meaningful information, suggesting that DXA measurements could be a useful screening tool in routine medical examinations to predict stress fractures in female long-distance runners, which may assist preventive programs or protocols.