Kinematic and Coordination Variability in Runners with and Without Patellofemoral Pain

Background: Patellofemoral pain (PFP) is a common overuse injury that has been suggested to cause abnormal gait kinematics and variability in runners with PFP. Conflicting results have been presented as to the variability of joint kinematics and joint coordination. Objective: The purpose of this study was to examine the variability of lower extremity kinematics and joint coordination in the presence of PFP and exertion. Methods: Six female runners with PFP and matched controls (CON) ran at a self-selected pace on an instrumented treadmill until exertion or pain criteria was met. Sixteen anatomical retroreflective markers and seven tracking clusters were placed on the participants’ lower extremities. Data collected for 20 steps from the beginning, middle, and end of the run were processed. Kinematic variability was assessed for each participant by calculating the standard deviation (SD) of peak knee flexion, internal rotation, and adduction angle and their velocities. Continuous relative phase (CRP) mean values were calculated from normalized phase plots for coordination relationships between knee horizontal plane motion and hip sagittal, frontal, and horizontal and ankle frontal plane motion. Coordination variability was calculated as the CRP coupling SD over 100% of stance for each time point for each participant. Statistical comparisons were assessed through a 2 (PFP vs. CON) x 3 (beginning, middle, end) repeated measures ANOVA. Results: There was an increase in variability for peak knee adduction angle, peak knee adduction velocity, hip flexion/knee rotation CRP, and knee rotation/rearfoot eversion CRP over time for the PFP group compared with CON (P<0.05). Conclusion: Pain and exertion increase the variability of joint kinematics and joint coordination reflecting decreased movement control towards the end of a run.