Mild Traumatic Brain Injury and Subsequent Musculoskeletal Injury in US Service Members

Importance: Mild traumatic brain injury (mTBI) is associated with greater risk of musculoskeletal injury (MSKI). However, it is unclear whether mTBI is associated with risk of subsequent MSKI among US service members (SMs) with extended follow-up and whether this varies between male and female individuals. Objective: To test the association of mTBI with subsequent MSKI in a large study population of SMs with extended follow-up. Design, Setting, and Participants: This cohort study included SMs with mTBI and propensity score-matched controls who joined between 2016 and 2020 across all branches of the US military and had medical record data until 2023. Data were analyzed from December 2024 to October 2025. Exposure: Medical record-derived mTBI. Main Outcome and Measures: mTBIs and MSKI events were identified using International Statistical Classification of Diseases and Related Health Problems, Tenth Revision codes. To test associations of mTBI with subsequent overall MSKI, Cox proportional hazards and Aalen additive hazards models were fit to estimate relative and absolute effect sizes, respectively. Testing was completed for moderation by sex. All models were adjusted for demographic and military-relevant characteristics. Results: The mean (SD) age of the 26 784 participants (13 392 with mTBI and 13 392 controls without mTBI) was 20.0 (2.8) years, and 4585 (17.1%) were female. During 34 156 person-years of follow-up, there were 14 330 MSKI events. Compared with no mTBI, mTBI was associated with a greater hazard of subsequent MSKI (hazard ratio [HR], 2.24; 95% CI, 2.16-2.32). On the absolute scale, mTBI, compared with no mTBI, was associated with an additional 258 MSKI events per 100 000 person-days (Aalen additive hazard = 2.58 × 10-3; SE, 1.17 × 10-6). Although there was no significant interaction in associations of mTBI with subsequent MSKI by sex (P for interaction = .37), mTBI was associated with greater hazard of MSKI in models among female SMs only (HR, 2.28; 95% CI, 1.92-2.70), and in models among male SMs only (HR, 2.20; 95% CI, 2.11-2.29). Conclusions and Relevance: In this cohort study of US SMs, mTBI was associated with greater hazard of subsequent MSKI on the relative and absolute scales. Female SMs had a greater hazard of MSKI, but there was no significant moderation by sex for associations between mTBI and MSKI. Findings can inform patient counseling on MSKI risk following mTBI.