Body-Worn Sensors for Risk of Injury Prediction During Military Training
More than 800,000 military service members are injured each year, leading to an estimated 25 million days of limited duty annually. Musculoskeletal injuries (MSI) are the greatest threat to force readiness during both peacetime and combat operations. Although the more severe trauma during combat can lead to a significant loss of military personnel, even seemingly mild injuries during sport and exercise could contribute to a lack of readiness and poorer overall fitness. Furthermore, non-combat MSI (during physical training, tactical training, recreational activity, and sport) are endemic within the military population accounting for 85% of all MSI among United States (U.S.) military personnel. Athletic injuries are also the leading cause of disability discharge among service members (SM) in the U.S. Army, according to Physical Evaluation Board data. Thus, prevention and care of these sports and physical training injuries are top priorities for leaders in the Department of Defense (DoD).
Most sports-related MSI affect the lower limb. Forty percent of these injuries occur at the knee, making it the most common site of MSI. Specifically, soft tissue injuries are the most frequently encountered and represent 47% of all knee injuries. In the U.S., fibrocartilage, ligamentous, and tendinous integrity compromise about the knee can lead to joint instability. Knee joint instability can have short-term and/or long-term negative effects, affecting force readiness and return-to-duty/return-to-sport (RTD/RTS) decisions. Objective measures of knee stability could be used to determine those at risk for injury thus decreasing the rate of injury. In addition, objective measures of knee stability could be used throughout the rehabilitation process to determine healing and neuroadaptation of soft tissue and surrounding contractile musculature, respectively, enabling the SM to RTD/RTS without fear of re-injury and with a greater potential to achieve their pre-injury level of performance.
Effective measures of injury risk and function are urgently needed in the military and athletic populations. Traditional functional assessment tests such as the hop test and vertical drop jump tests are currently used to determine time of return to preoperative physical activity level following knee injury and used as a clinical screening tool for anterior cruciate ligament (ACL) injury, respectively. However, the sensitivity for detecting functional weaknesses, i.e. single-leg hop test for distance, is reported to be between 38-52%. It was also recently reported that none of the vertical drop jump test variables were associated with increased ACL injury risk in a cohort study of 710 athletes. Often, by the time the test results are known the functional status of the healing individual has changed or the individual has made the decision to return to activity.
The use of mobile technologies and body-worn devices for the classification of at-risk SMs with MSI can be performed in a matter of minutes with real-time analysis. Predicting which SMs are at risk for injury prior to an adverse event can have a major impact on their health, career, and the cost of care for the military.
To assess the risk for knee injury efficiently, we have previously developed a novel mobile lower limb motion capture system (known as CaneSenseTM) consisting of small wireless inertial measurement units (IMUs) that communicate via Bluetooth to a custom mobile app on a mobile tablet. Data is processed in real time and includes kinematics and kinetics to improve functional outcomes.