Background: Excessive knee valgus moments are considered a risk factor for non-contact anterior cruciate ligament injuries in female athletes, however, little is known about the biomechanical factors that contribute to this loading pattern. The purpose of this study was to compare lower extremity kinematics, foot position and ground reaction forces between female soccer players who demonstrate normal frontal plane moments at the knee with those who demonstrate excessive frontal plane moments at the knee during a cutting maneuver.
Methods: Sixty-one female soccer players, 16 (2) years, participated. Three dimensional kinematics and ground reaction forces were recorded during a side-step cutting maneuver. Knee frontal plane moments were calculated with inverse dynamics equations and were used to classify subjects into normal (N=38) and excessive valgus moment (N=23) groups.
Findings: Data revealed that the subjects with excessive valgus moments demonstrated an initial loading pattern that included greater laterally directed ground reaction forces (P<0.001, effect size 1.51), increased hip abduction (P=0.002, effect size 0.79), increased hip internal rotation (P=0.008, effect size 0.71) and a more internally rotated foot progression angle (P=0.04, effect size 0.55). Taken together, these variables explained 49% of the variance in peak knee valgus moment (R=.698, P<0.001).
Interpretation: These results provide insight into potentially injurious loading strategies and support the premise that interventions designed to encourage loading of the lower extremity in a more neutral alignment may work to decrease frontal plane loading at the knee.