Risk Factors for Lower Extremity Overuse Injuries in Female Youth Soccer Players

BACKGROUND: Youth soccer injuries are common and of increasing concern, with sport specialization occurring at younger ages. Limited research is available regarding overuse injuries and risk factors in young female athletes. PURPOSE: To identify the number and rate of overuse injuries in female soccer players (ages 12-15 years), describe the anatomic location and type of injury, and evaluate contributing risk factors. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: A total of 351 female youth soccer players, ages 12 to 15 years, from Washington State were evaluated from 2008 to 2012. Players with lower extremity overuse injuries were identified through weekly emails and were interviewed by telephone to obtain data on injury type and body region. We evaluated the association between overuse injuries and preseason risk factors, including joint hypermobility, hip and knee muscle strength, and jump biomechanics, using Poisson regression to estimate relative risk (RR) and 95% CIs. RESULTS: The incidence rate for first-time lower extremity overuse injuries was 1.7 per 1000 athlete-exposure hours (AEH; 95% CI, 1.4-2.2), and that for repeat injuries was 3.4 per 1000 AEH (95% CI, 2.1-5.6). Knee injuries accounted for 47% of overuse injuries. Increased valgus was associated with a 3.2-fold increased risk (95% CI, 1.52-6.71) for knee injury. A 1–standard deviation (SD) increase in hamstring strength was associated with a 35% decreased risk (RR, 0.65; 95% CI, 0.46-0.91) for overuse knee injuries, and a 1-SD increase in quadriceps strength was associated with a 30% decreased risk (RR, 0.70; 95% CI, 0.50-0.98). A 1-SD increase in hip flexor strength was associated with a 28% decreased risk (RR, 0.72; 95% CI, 0.51-1.00) for overuse knee injuries, and a 1-SD increase in external rotation strength was associated with a 35% decreased risk (RR, 0.65; 95% CI, 0.46-0.91). Playing on more than 1 soccer team was associated with a 2.5-fold increased risk (95% CI, 1.08-5.35) for overuse knee injuries, and participating in other physical activities was associated with a 61% decreased risk (odds ratio, 0.39; 95% CI, 0.15-0.81). CONCLUSION: In this study, lower extremity overuse injuries in female youth soccer players affected primarily the knee. Lower knee separation distance, decreased lower extremity strength, and playing on more than 1 soccer team increased injury risk.