Investigation of lower limb stress fractures in university long-distance runners: characteristics of pelvic and femoral stress fractures.

PURPOSE: The distribution of bone stress injuries (BSIs) in distance runners may have changed following the widespread adoption of maximalist running shoes. However, site-specific incidence patterns in elite collegiate athletes remain unclear. We investigated the incidence and characteristics of lower-extremity BSIs in an elite university distance-running team. METHODS: Between April 2022 and October 2025, a retrospective observational study was conducted on a single elite collegiate distance-running team, for whom medical records were reviewed to identify lower-extremity and pelvic BSIs, with incidence rates being calculated per 100 athlete-years (AYs). Symptom-resolution periods were compared among magnetic resonance imaging (MRI) grades. Seasonal incidence rates were analysed using incidence rate ratios. RESULTS: Ninety-two athletes contributed 172 AYs. Fifty-one BSIs were identified, corresponding to an overall incidence of 29.7 per 100 AYs. The femur was the most common site of injury (21 cases/41%). The incidence of proximal BSIs involving the pelvis and femur was 18.6 per 100 AYs, compared with 11.0 per 100 AYs for distal lesions involving the lower leg and foot. The incidence in winter was significantly lower than in spring. All femoral Grade 4 lesions showed longitudinal marrow signal abnormalities on MRI. CONCLUSIONS: Among these elite collegiate distance runners, femoral BSIs were the most common injury, with proximal lesions occurring more frequently than distal, and longitudinal marrow signal abnormalities on MRI characteristic of femoral injuries. These findings may facilitate earlier recognition of proximal BSIs in competitive runners.