AGE, BODY MASS INDEX AND SEX RELATED TO DYNAMIC KNEE VALGUS AND SHOCK ABSORPTION DURING SINGLE LEG LANDING IN UNINJURED ADOLESCENT ATHLETES

Abstract

BACKGROUND Dynamic limb valgus and poor shock absorption strategies have been implicated in anterior cruciate ligament (ACL) injuries. Additionally, biomechanics during over ground and double leg landing tasks have been shown to differ depending on sex and age/maturation. However, there is limited evidence evaluating the effect of age, body mass index (BMI) and sex on single leg landing strategies. METHODS 51 uninjured athletes (ages 7-15 years, mean 12.2, SD 2.3; 45% female) completed the single leg hop (SLH) for distance task. 3-D motion analysis using a 6 degree-of-freedom model was used to collect lower extremity kinematics and kinetics from initial foot contact to peak knee flexion of landing limb; for each limb the hop with the longest distance and appropriate landing (stuck for >2 seconds) was used for analysis. Using multivariate regression with standardized coefficients, the effects of age, BMI and sex on biomechanical variables of interest were assessed. RESULTS When considering dynamic valgus components, younger age was associated with higher knee valgus (ß=0.251; p=0.038) and hip abduction (ß=0.250; p=0.038) angles, higher BMI was associated with higher knee valgus angles (ß=0.262; p=0.028), and females tended to have higher hip abduction moments (ß=0.301; p=0.003), but a more abducted (ß=0.281; p=0.005) and internally rotated hip position (ß=0.359; p=0.003) along with higher internal rotation hip moments (ß=0.298; p=0.001) and with higher ankle inversion moments (ß=0.304; p=0.003). Although differences were observed, R2 values were low ranging from 0.191 (hip ab/adduction angles) to 0.053 (knee valgus moment). Sagittal plane components of shock absorption were partially explained by age, BMI and sex (R2 values range from 0.685 to 0.013; vertical ground reaction force (vGRF) in multiples of body weight, ankle dorsi/plantarflexion moment, respectively). Younger age was associated with higher vGRF (ß=-0.520; p<0.0001) and knee flexion moments (ß=-0.225; p=0.034), but with lower knee flexion angles (ß=0.252; p=0.041), ankle dorsiflexion angles (ß=0.322; p=0.003) and hip flexion moments (ß=0.289; p=0.016). Higher BMI was associated with lower GRF (ß=-0.387; p<0.0001), lower knee (ß=-0.277; p=0.009) and hip (ß=-0.289; p=0.043) flexion moments and lower sagittal plane energy absorption at the knee (ß=-0.267; p=0.016). Females tended to have lower vGRF (ß=0.147; p=0.017), more sagittal plane hip (ß=0.282; p=0.007) and knee (ß =0.250; p=0.010) energy absorption and less ankle dorsiflexion (ß=-0.283; p=0.002). CONCLUSION/SIGNIFICANCE Biomechanical risk factors for ACL injury during single leg hop landings are influenced by age, BMI and sex. Female sex and higher BMI are associated with dynamic limb valgus while younger age is associated with both dynamic limb valgus and poor shock absorption during single leg hop landings. These are important findings due to the known ACL injury risk in female athletes and the high re-tear rate in pediatric athletes. Identifying these biomechanical risk factors related to demographics and anthropometrics may provide objective direction needed to contribute to effective intervention strategies and eventual injury reduction in these high risk groups.