Background Many studies have explored the risk factors for noncontact anterior cruciate ligament (ACL) injuries.

Objective To prospectively evaluate risk factors for noncontact ACL injury in Japanese female high school basketball and handball players. We hypothesized those female high-school athletes suffering non-contact ACL injuries would demonstrate weaker hip abductor and knee flexor muscle strength, when compared to those without injury.

Design Prospective cohort study.

Setting & Participants A 3-year prospective cohort study was conducted using 317, 15-year-old high school female athletes between 2009 and 2014. At baseline, they underwent detailed examinations for various parameters that were documented at their first-year of high school.

Assessment of Risk Factors The parameters assessed were height, weight, body mass index, general joint laxity, navicular drop measurement, anterior laxity of the knee, and angle of femoral anteversion, and strength assessment included knee extensor/flexor muscle strength and hip abductor strength. All ACL injuries that occurred during these 3 years were recorded. The parameters were compared using the Student t-test. Parameters with P values<0.2 were considered independent variables by logistic regression analysis (simultaneous). The level of significance for all statistical analyses was set at α=0.05.

Results Of the 317 players, 27 were excluded because they either had a history of ACL injury or could not complete the study. A total of 30 ACL tears occurred. Three of the ACL injuries were contact injuries, whereas the remaining 27 were noncontact ACL injuries. Muscle strength of hip abduction (P=0.001, 95% CI, 1.793–67.534) and femoral anteversion (P=0.037, 95% CI, 0.759–0.991) were found to be independent risk factors in logistic regression analysis.

Conclusions We found that increased hip abductor muscle strength and decreased femoral anteversion were risk factors for noncontact ACL injury. However, there was only a little difference.