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The influence of patellofemoral pain on muscle coordination, segment coordination, and segment coordination variability in runners

Management of patellofemoral pain syndrome (PFPS) remains a significant challenge in clinical practice and there is a need to understand the mechanisms for altered gait and muscular function which may lead to poor patient outcomes. The overall aim of the three studies in this dissertation was to determine if runners with current PFPS adapt their gait and muscle activation as a result of long-term, daily pain and/or in response to an acute pain flare and exertion during a moderate intensity 21-minute treadmill run compared to healthy controls. In addition, a resolved, asymptomatic PFPS group was included to investigate potential mechanisms for the frequent reoccurrence of pain experienced by those with a history of PFPS. The lack of differences in baseline kinematic, segment coordination, and segment coordination variability measures suggest that there are no long-term gait adaptations to pain in either injury group that manifest as resultant gait patterns. Several differences were identified in baseline kinetics among all three groups for peak hip abduction and external rotation as well as ankle inversion moments. These findings indicate that: 1) runners with a history of PFPS have different loading patterns at the hip and ankle compared to healthy runners and 2) these altered loading patterns are not substantial enough to alter resultant kinematic patterns of movement. In addition to these joint moments, altered muscle coordination discriminated between all three groups. These findings have significant implications for identifying individuals at risk of re-injury and helping to improve treatment efficacy in runners with PFPS. Movement evoked pain is a primary characteristic of PFPS, and the treadmill run used in these studies was sufficient to cause a pain response in the injured group. Changes seen in the outcome measures of the three studies at the end of the run are indicative of a response to a combination of increased pain and exertion. Greater anti-phase motion of the sagittal thigh-transverse shank in the injured group compared to controls suggests that altered movement control about the knee may be related to increased pain in those with PFPS. In addition to the decreased coordination variability observed in those with PFPS, there were also differences in coordination variability between the resolved and control groups, with the resolved group often showing increases in variability compared to controls. This suggests that abnormal movement flexibility may persist even once painful symptoms are resolved and that individuals with a history of PFPS do not return to healthy gait patterns following resolution of symptoms.
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