Association Between a History of Contact Sport Participation and Higher Lifetime Mild Traumatic Brain Injury Burden Among Military Servicemembers and Veterans: A Long-term Impact of Military-relevant Brain Injury Consortium–Chronic Effects of Neurotrauma Consortium Prospective Longitudinal Study (LIMBIC-PLS)

Background: Both years of contact sport participation and years of military service are positively related to risk of sustaining multiple mild traumatic brain injuries (mTBIs). Little is known about the additive risk of mTBI exposure by combining premilitary contact sport participation with subsequent military service. Purpose: To assess the effect of premilitary contact sport participation on the odds of current and former military personnel sustaining mTBI(s) during their lifetime. Study Design: Cross-sectional study; Level of evidence, 3. Methods: This study analyzed data from 2651 individuals from the LIMBIC-PLS. The association between a history of contact sport participation and sustaining an mTBI pre–military service, during military service while not on deployment, or during deployment was estimated using odds ratios. The association between the total number of pre–military service, military service while not on deployment, and deployment-related mTBI events with history of contact sport participation (yes vs no) was estimated using incidence rate ratios (IRRs) and 95% confidence intervals. The authors adjusted those models for demographic factors and then repeated those analyses using years of contact sport exposure, categorized as 0 (referent), >0 to 5, >5 to 10, and >10 years. Results: In this cohort, 62% had a history of contact sport participation and 82% had a history mTBI. Individuals with a history of contact sport participation were more likely to have experienced an mTBI in their lifetime (OR, 1.26; 95% CI, 1.03-1.54; P = .023). This manifested only outside of military combat deployments. Specifically, a history of contact sport exposure was associated with a higher odds of an mTBI before military service (OR, 1.63; 95% CI, 1.39-1.91; P < .001) or a nondeployment mTBI (OR, 1.62; 95% CI, 1.37-1.91; P < .001) Moreover, a higher incidence rate of lifetime mTBI was observed as number of years of contact sport exposure increased. Conclusion: Similar to findings in civilians, these findings suggest that contact sport participation increases the likelihood of experiencing a single or multiple mTBI events among military personnel. These findings suggest that it would be appropriate to screen individuals’ mTBI history before joining the military to identify individual potential risks for concerns associated with multiple lifetime mTBI events.