Lower Extremity Musculoskeletal Injuries in United States Active Duty Service Members: Prevalence/Incidence, Health Care Utilization, and Cost Analysis Spanning Fiscal Years 2016-2021.

Introduction: Lower Extremity musculoskeletal injuries (LE MSKIs) represent a significant portion of overuse injuries in active duty service members (ADSMs). However, variations in study methods and research gaps related to LE MSKIs have prevented Department of Defense (DoD) leaders from assessing the burden of these conditions. The purpose of this study was to report the incidence, prevalence, and types of LE MSKIs sustained by ADSMs across four branches of service and describe associated health care utilization and private sector costs.

Materials and methods: This was a retrospective, longitudinal population study, including ADSMs from the Air Force, Army, Marine Corps, and Navy. Prevalence and incidence rates for LE MSKIs, associated health care utilization, and costs were obtained by querying electronic health records (EHR) from military treatment facilities (MTFs), private sector care (PC) claims, and theater medical data from the Military Health System Data Repository (MDR) from October 1, 2015 to September 30, 2021 (FY16-21). Utilization associated with LE MSKIs in both the direct care (DC) and PC settings was classified into mutually exclusive outpatient encounter categories and acute inpatient stays. PC costs related to LE MSKIs were captured for each year.

Results: In FY21, LE MSKIs occurred in 25.3% of ADSMs (n = 378,615). A higher proportion of females sustained an LE MSKI (33.3%), compared to males (23.7%). From FY16-21, the Army had the highest annual prevalence of LE MSKIs (30.9-35.5%), followed by the Air Force (23.8-31.0%), Marine Corps (23.4-27.0%), and Navy (17.2-19.8%). Incidence rate patterns were similar, with the Army sustaining LE MSKIs at 320 to 377 injuries per 1,000 person-years, followed by the Air Force (241-318), Marines (255-288), and Navy (173-203). Overuse/non-specific MSKIs of the knee were the most common injury type and body region affected, respectively. There were 10,675,543 DC and 1,875,307 PC outpatient encounters from FY16-21 with a primary or secondary diagnosis of LE MSKI. The Air Force was most reliant on PC, with 21.5 to 36.8% of LE MSKI-related encounters occurring outside MTFs during FY16-21. Over $99 million was paid by TRICARE on LE MSKI in FY21 alone with Same Day Surgeries accounting for almost half ($48 million) of this total.

Conclusions: Among U.S. ADSMs, LE MSKIs remain highly prevalent and costly. We observed disparities across the Services in the prevalence and incidence of LE MSKIs, and their respective reliance on the private sector for management of these conditions. Findings from this work may support military leaders and MSKI researchers who seek to reduce the impact of LE MSKIs on the readiness and overall health of the U.S. Military.