Association of Injury History and Incident Injury in Cadet Basic Military Training

Purpose This study aimed to determine the association between injury history at enrollment and incident lower extremity (LE) injury during cadet basic training among first-year military cadets. Methods Medically treated LE injuries during cadet basic training documented in the Defense Medical Surveillance System were ascertained in a prospective cohort study of three large US military academies from 2005 to 2008. Both acute injuries (International Classification of Disease, Ninth Revision, codes in the 800-900s, including fracture, dislocations, and sprains/strains) and injury-related musculoskeletal injuries (International Classification of Disease, Ninth Revision, codes in the 700s, including inflammation and pain, joint derangement, stress fracture, sprain/strain/rupture, and dislocation) were included. Risk ratio (RR) and 95% confidence interval (CI) were computed using multivariate log-binomial models stratified by gender. Results During basic training, there were 1438 medically treated acute and 1719 musculoskeletal-related LE injuries in the 9811 cadets. The most frequent LE injuries were sprains/strains (73.6% of acute injuries) and inflammation and pain (89.6% of musculoskeletal-related injuries). The overall risk of incident LE injury was 23.2% (95% CI = 22.3%-24.0%). Cadets with a history of LE injury were at increased risk for incident LE injury. This association was identical in males (RR = 1.74, 95% CI = 1.55-1.94) and females (RR = 1.74, 95% CI = 1.52-1.99). In site-specific analyses, strong associations between injury history and incident injury were observed for hip, knee ligament, stress fracture, and ankle sprain. Injury risk was greater (P < 0.01) for females (39.1%) compared with males (18.0%). The elevated injury risk in females (RR = 2.19, 95% CI = 2.04-2.36) was independent of injury history (adjusted RR = 2.09, 95% CI = 1.95-2.24). Conclusion Injury history upon entry to the military is associated with the incidence of LE injuries sustained during cadet basic training. Prevention programs targeted at modifiable factors in cadets with a history of LE injury should be considered.