This investigation sought to quantify incidence rates (IRs) and risk factors for primary and secondary (ie, posttraumatic) osteoarthritis (OA) of the knee in an active military population.

We performed a retrospective review of United States military active duty servicemembers with first-time diagnosis of primary (International Classification of Disease, 9th Edition code: 715.16) and secondary (International Classification of Disease, 9th Edition code: 715.26) OA of the knee between 2005 and 2014 using the Defense Medical Epidemiology Database. IRs and 95% CIs were expressed per 1000 person-years, with stratified subgroup analysis adjusted for sex, age, race, military rank, and branch of military service. Relative risk factors were evaluated using IR ratios and multiple regression analysis.

A total of 21,318 cases of OA of the knee were identified among an at-risk population of 13,820,906 person-years for an overall IR of 1.54 per 1000 person-years, including 19,504 cases of primary (IR: 1.41) and 1814 cases of secondary OA (IR: 0.13). The IRs of both primary and secondary OA increased significantly from 2005 to 2014. Increasing age (P < .0001); black race (P < .001); senior military rank (P < .0001); and Army, Marines, and Air Force services (P < .0001) were significantly associated with an increased risk for knee OA.

This study is the first large-scale report of knee OA in a young athletic population. An increasing incidence and several risk factors for knee OA were identified, indicating a need for better preventative strategies and forecasting the increased anticipated demands for knee arthroplasty among US military servicemembers.