Longitudinal Increases in Knee Abduction Moments in Females during Adolescent Growth

PURPOSE: Knee abduction moment (KAM) is an injury risk factor for anterior cruciate ligament (ACL) injury that shows divergent incidence between males and females during adolescence. The objective of this study was to determine the relation between skeletal growth and increased KAM. The hypotheses tested were that females would demonstrate peak KAM during landing at peak height velocity (PHV) and that they would diverge from males at PHV. METHODS: The subject pool consisted of 674 females and 218 males (1387 female and 376 male assessments) who participated in a preseason testing session before their basketball or soccer seasons. They were tested longitudinally for multiple years (2 ± 1 yr) to capture maturation via estimates of percent (%) adult stature and biomechanical analysis during a drop vertical jump maneuver. Data were analyzed using three-dimensional motion analysis that used a 37 retroreflective marker body model and inverse dynamics to calculate segment joint centers and peak KAM. RESULTS: Mature females, as defined as 92% adult stature or greater, displayed increased peak KAM and knee abduction angles relative to growing (≤91% adult stature) adolescent females (P < 0.001). A significant sex–maturation (% adult stature) interaction (P < 0.001) in peak KAM was observed. Post hoc analyses showed consistent sex differences in groups greater than or equal to, but not less than, 92% adult stature, which is approximately at PHV. Hence, sex differences in peak KAM and PHV coincide. CONCLUSIONS: Increases in peak KAM during and after PHV seem to coincide with increased risk of ACL injury in females. KAM peaked in females at PHV. Tracking longitudinal increases in peak KAM may be useful for the identification of females at increased risk of ACL injury.