Differences in peak knee valgus angles between individuals with high and low Q-angles during a single limb squat.

Background: Differences in anatomical alignment between genders have been suggested as causes of the disparity in anterior cruciate ligament injury rates. A larger Q-angle may be associated with increased knee valgus during movement resulting in anterior cruciate ligament strain. This study investigated whether healthy college-aged subjects with a large Q-angle display greater peak knee valgus during a single limb squat compared to those with a small Q-angle. The study also determined whether the high and low Q-angle groups displayed differences in other select anatomical variables, and whether these anatomical variables were related to knee valgus.

Methods: Twenty subjects, categorized as having a "high Q-angle" (> or = 17 degrees) or a "low Q-angle" (< or = 8 degrees) were videotaped during the performance of a single leg squat. The peak valgus angles for the right knee were calculated. One-tailed independent measures t-tests were used to determine whether individuals with a large Q-angle exhibit (1) significantly greater peak knee valgus during a single leg squat compared to those with a small Q-angle and, (2) greater pelvic width to femoral length ratios and greater static knee valgus than subjects with a small Q-angle. The Pearson product-moment correlation was used to establish the relationships between pelvic width to femoral length ratios and static knee valgus, pelvic width to femoral length ratios and dynamic knee valgus, and static knee valgus and dynamic knee valgus.

Findings: Peak knee valgus during the single leg squat, and static knee valgus were not significant greater in the high Q-angle group compared to the low Q-angle group (P=0.09; P=0.31). Subjects with a larger Q-angle, however, had a significantly greater pelvic width to femoral length ratios (P=0.015) compared to subjects with a small Q-angle. Pelvic width to femoral length ratios was related to both static and dynamic knee valgus (r=0.47, P=0.02; r=0.48, P=0.02), but static knee valgus was not related to dynamic knee valgus.

Interpretation: The findings suggest that pelvic width to femoral length ratios, rather than Q-angle, may be a better structural predictor of knee valgus during dynamic movement.