Patellofemoral pain syndrome (PFPS) is the most common injury in runners. Hip mechanics have recently been shown to play an important role in the development of PFPS in runners. However, there are no interventions that directly attempt to address these underlying faulty mechanics. Additionally, the reliability of these measures over time is poor. Lastly, current gait analysis techniques do not allow the valid measurement of patellofemoral alignment, limiting our understanding of the mechanisms related to this disorder

Three studies were undertaken to address these gaps in the literature. The purpose of the first study was to determine whether day-to-day kinematic reliability can be improved with the use of a marker placement device. We hypothesized that the use of the marker placement device would result in higher ICC and lower SEM values than manual marker placement. We found that day-to-day reliability was substantially improved when using the marker placement device. The second aim sought to determine if individuals with PFPS can be trained to run with improved hip mechanics using real-time kinematic feedback. We hypothesized that gait retraining would result in a decrease in hip adduction, internal rotation and contra-lateral pelvic drop. Additionally, we hypothesized that these improvements in mechanics would be associated with reduction in pain and improvement in function. We also hypothesized that the improvement in hip mechanics would transfer to the single leg squat. Lastly, we hypothesized these changes would be maintained at the one month follow-up. We found that there was a significant improvement in hip adduction and contralateral pelvic drop after gait retraining. There was also a significant reduction in pain and improvement in function. Although not statistically significant, there was a 19% reduction in hip adduction during a single leg squat, indicating a transfer to an unpracticed skill. The kinematic and functional changes following gait retraining were maintained at the one month follow-up. The persistence of these changes, along with the transfer to the single leg squat indicate that learning had occurred. The third aim of this study was to determine the effect of altering hip mechanics on patellofemoral alignment during a single leg squat using MRI. We hypothesized that the valgus squat would result in more tibiofemoral external rotation and abduction compared to the neutral squat. We also expected the valgus squat would result in greater patellofemoral lateral tilt and displacement. We found the valgus squat resulted in greater knee external rotation in all subjects. These alterations in patellofemoral alignment may change the contact stress, and with repeated exposure, result in pain.

Theses studies have provided insights into the mechanics related to PFPS. The primary finding was that real-time gait retraining was successful in improving results in mechanics, as well as reducing pain and improving function. Additionally, the improvement in the kinematic reliability allows for greater confidence when conducting studies requiring multiple kinematic measures over time. Lastly, the results from the MRI study would suggest that hip mechanics can influence patellofemoral kinematics in some subjects.