High Body Mass Index and Hip Abductor Muscle Strength were Risk Factors for Non-contact ACL Injury in Female High School Basketball Players: A Prospective Three-year Cohort Study

OBJECTIVES: To prospectively evaluate risk factors for non-contact anterior cruciate ligament (ACL) injury in female high school basketball players. We hypothesized that female high-school basketball players suffering non-contact ACL injuries would demonstrate weaker hip abductor and knee flexor muscle strength and poor static balance, when compared to those without ACL injury. METHODS: Study Design: Prospective cohort study.195 new female high school basketball players underwent detailed examinations for various parameters that were documented at their first-year of high school. The parameters assessed were height (cm), body weight (kg), body mass index (kg/m(2)), anterior knee laxity (mm), general joint laxity (point), femoral anteversion (degree), navicular drop (mm), muscle strength of knee flexion (Nm/kg), extension (Nm/kg), and hip abduction (Nm/kg) and static balance. All ACL injuries that occurred during these 3 years were recorded. The data were analyzed using SPSS for Windows 23.0. 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 195 players, 24 were excluded because they either had a history of ACL injury or could not the study. The remaining 171 players were observed during the 3 years, from start of high school until graduation. A total of 16 ACL tears occurred. One of the ACL injury were contact injury, whereas the remaining 15 were noncontact ACL injuries. Nine players were injured during the games, 7 were injured during practices. The parameters were measured as follows for the ACL injury group and control group respectively: height, 161.3 ± 6.7 and 162.0 ± 5.7 cm, P = 0.63; body weight, 57.5 ± 7.8 and 55.4 ± 6.2kg, P = 0.22; body mass index, 22.1 ± 1.8 and 20.1 ± 2.7, P= 0.17; anterior knee laxity, 4.0 ± 1.0 and 3.8 ± 1.1 mm, P = 0.54;, general joint laxity, 1.8 ± 1.3 and 2.7 ± 2.2 points, P = 0.03; femoral anteversion, 16.2 ± 3.7 and 16.7 ± 3.3 degree, P = 0.60; navicular drop, 8.5 ± 6.2 and 8.0 ± 3.3 mm, P = 0.78; muscle strength of knee flexion, 0.97 ± 0.27 and 0.89 ± 0.20 Nm/kg, P = 0.17; muscle strength of knee extension, 1.73 ± 0.39 and 1.58 ± 0.35 Nm, P = 0.14; muscle strength of hip abduction, 1.42 ± 0.32 and 1.26 ± 0.24 N, P = 0.02; locus length per time, 1.35 ± 0.39 and 1.16 ± 0.26 cm/s, P = 0.09; and environmental area, 2.62 ± 1.64 and 2.20 ± 1.22 cm(2), P = 0.37 (Table 1). Body mass index (P=0.008, 95% CI, 0.517-0.904) and muscle strength of hip abduction (P = 0.032, 95% CI, 0.002-0.477) were found to be independent risk factors in logistic regression analysis (Table 2). CONCLUSION: The most notable finding of this study was that greater hip abductor muscle strength is a risk factor for non-contact ACL injury in these athletes. This study is the first to identify the relationship between non-contact ACL injury and hip abductor muscle strength.