Effect of Lower Extremity Static Alignment on Dynamic Valgus in Adolescents Following ACL Reconstruction

Abstract

PURPOSE: Knee abduction moments may lead to valgus collapse, potentially causing ACL rupture. The contribution of static lower extremity alignment to knee abduction moments is unknown. This study assessed relationships among lower extremity static alignment and dynamic kinematics and kinetics during side-step cutting in uninjured adolescent athletes. METHODS: This retrospective study included 8 adolescents with recent unilateral ACL reconstruction (mean age 14.8 yr, SD 1.2; 3/8 female). Frontal plane hip to ankle imaging (EOS) was used to measure mechanical axis deviation (perpendicular distance from the center of the femoral condyles to the mechanical axis line connecting the center of the femoral head to the center of the talar dome) and tibial-femoral angle. 3D motion capture provided lower extremity kinematics and kinetics during quiet standing and loading (initial contact to peak knee flexion) of an anticipated 45° side-step cut; 2-3 trials per limb were averaged for analysis. Relationships among imaging, static motion capture and dynamic motion capture measures were investigated using correlation, and backward stepwise linear regression was used to evaluate potential predictors of average dynamic knee abduction moment. RESULTS: Regardless of surgical status, standing knee abduction angle was correlated with standing hip adduction (r=0.60, p=0.02) and ankle eversion (r=0.85, p<0.0001) along with larger mechanical axis deviations (r=0.83, p=0.0001) and higher knee abduction on EOS (r=0.44, p=0.09). Dynamic knee abduction moment was best predicted by a combination of EOS knee abduction angle, standing ankle eversion, standing knee abduction, standing knee rotation, ankle eversion during cutting, along with ground reaction force and age (R2=0.94; p<0.004). There was no significant relationship between knee abduction moment and side (surgical vs. contralateral) (p=0.63). CONCLUSIONS: In this small group of adolescent athletes with recent ACLR, knee abduction moment during side-step cutting was related to age and anatomic lower limb alignment in addition to dynamic factors such as ankle positioning and ground reaction force. Anatomic alignment or standing posture with greater hip adduction, knee abduction, and ankle eversion may indicate a higher risk for injury during dynamic activities.