Q-angle influences on the variability of lower extremity coordination during running

The quadriceps angle (Q-angle) has received attention as a possible predictor of patellofemoral pain (PFP). It has been suggested that an excessive Q-angle alters the patellofemoral tracking, thereby leading to PFP. Traditional methods used to evaluate alterations in lower extremity angular kinematics have not confirmed this thought. A dynamical systems approach involving segment couplings may provide additional insight by addressing the variability of the intersegmental coordination.

Thirty-two healthy pain-free subjects with varying Q-angles were examined and divided into groups based on gender and Q-angle. Subjects ran overground for 10 trials while three-dimensional kinematic data were collected from the thigh, leg, and foot. The kinematic data were digitized and filtered before a direct linear transformation was employed to calculate three-dimensional segment angles and angular velocities. The variability of the continuous relative phase (CRP) of segment couplings was used to assess between-trial consistency at specific stance phase intervals.

No differences in CRP variability were found among subjects with varying Q-angles. Significant differences were present between the specific intervals of the couplings with the greatest variability during initial stance (P < 0.05).

A difference in CRP variability does not appear to exist in the lower extremity between individuals with and without abnormal Q-angles. The significant differences among the stance phase intervals of running suggest the inherent presence of coordination pattern variability. The importance of the increased pattern variability during initial stance may be associated with maintaining external stability.