MRI Findings of Femoral Neck Bone Stress Injuries in Army Trainees and Their Association with Basic Training Graduation: A Retrospective Cohort Study

PURPOSE: Femoral neck bone stress injuries (FNBSIs) are severe overuse injuries associated with high rates of noncompletion of training and medical separation in military personnel. While the negative impact of an FNBSI diagnosis is known, it remains unclear how specific magnetic resonance imaging (MRI)-defined injury characteristics, such as grade, location, and unilateral versus bilateral presentation, relate to graduation outcomes. This study aimed to determine the association between these FNBSI characteristics and graduation from Basic Combat Training (BCT). METHODS: In this matched retrospective cohort study of 208,540 U.S. Army trainees (2015-2019), trainees with MRI-confirmed FNBSIs ( n = 682) were matched 1:3 by sex and age to controls without bone stress injuries ( n = 2046). Logistic regression was used to model the associations between FNBSI features and BCT graduation. RESULTS: Graduation rates were significantly lower for trainees with an FNBSI, with matched controls having seven times higher odds of graduating (odds ratio [OR] = 7.38, 95% confidence interval: 5.95-9.16). Lower MRI grades were associated with significantly higher odds of graduation (e.g., grade 1 vs. 3, OR = 4.65), while bilateral injuries were associated with lower odds of graduation than unilateral injuries (OR = 0.72, 95% confidence interval: 0.53-0.98). No significant difference was observed between compression- and tension-sided injuries. In the matched cohort, male sex and older age were also associated with higher graduation odds. CONCLUSIONS: FNBSIs are strongly associated with lower odds of completing BCT, particularly when injuries are bilateral, of a higher MRI grade, or occur in younger or female trainees. These findings highlight the critical need for early detection, standardized reporting of MRI injury characteristics, and targeted interventions to improve military training retention.