Patellofemoral Joint Pain Study Title: Differences in hip kinematics, muscle strength, and muscle activation between subjects with and without patellofemoral pain Authors: Souza RB, Powers CM Publication Information: Journal of Orthopaedic & Sports Physical Therapy 2009; 39(1): 12-19. BACkgROuND INFORMATION: Patellofemoral joint (PFJ) pain is a common and often perplexing clinical condition that is still poorly understood. Recently it has been suggested that PFJ stress can result from improper mechanics or motor control of proximal structures. More specifically, altered kinematics of the femur and hip joint have been implicated in abnormal patellar tracking and pain syndromes in the anterior knee1-3 . One of the most prevalent mechanisms thought to contribute to PFJ pain is increased femoral (and hip) internal rotation, both static and dynamic. Various researchers have sug- gested that structural internal rotation of the femur with diminished dynamic control of inter- nal rotation during weight-bearing activities is a possible injury mechanism in PFJ pain. With increased internal rotation, PFJ stress increases1 and a dynamic valgus of the lower extremity occurs, resulting in higher forces acting laterally on the patella. Proper hip muscle activation, strength, and timing, particularly in the gluteus medius and maximus, could combat these mechanisms. Based on these concepts, the aim of this study was to determine whether females with PFJ dr. Shawn Thistle is the founder and president of research review Service inc., an online, subscription- based service designed to help busy practitioners to integrate current, relevant scientific evidence into their practice. Shawn graduated from CMCC and holds an hon- ours degree in Kinesiology from McMaster University. he also holds a certificate in Contemporary Medi- cal Acupuncture from McMaster University, and is a Certified Active release Techniques (ArT®) Pro- vider. For more information about the research review Service, visit www.researchreviewservice.com. pain demonstrate different hip mechanics and muscle strength measures compared to pain- free controls. PERTINENT RESuLTS: • When averaged across all tasks, the PFJ pain group demonstrated increased peak hip internal rotation during dynamic tasks (p < 0.001). • The largest difference in peak internal rotation between groups was observed during the running task. • No significant group effect was observed for hip adduction (this is contrary to other lit- erature in this area – see below). • PFJ pain subjects demonstrated lower strength in both isometric measurements – hip extension and hip abduction – compared to controls (p = 0.02 and 0.005 respectively). • EMG recordings revealed increased gluteus maximus (GM) activation in the PFJ pain group during the step-down (64 per cent greater) and running (91 per cent greater) tasks compared to controls (p = 0.041). This suggests that these patients are attempting to recruit a weakened muscle, perhaps to control hip rotation. • The fact that EMG activity of the GM was not greater during the drop jump task may be explained by the fact that this was a bilateral task (previous literature has demonstrated a difference during similar unilateral tasks). • EMG recordings were not significantly different between groups for the gluteus medius. CONCLuSIONS AND PRACTICALAPPLICATION: This study corroborates findings from previous studies2,3 which, taken as a whole, suggest that young female subjects with PFJ pain have altered hip kinematics and function compared to pain-free controls. Readers should remember that most studies on this condition are performed on females, as they have a much higher prevalence of this condition compared to males. Continued on Page 35 10 • CANAdiAN ChirOPrACTOr | JUNE 2009 www.canadianchiropractor.ca Shawn Thistle, BKin (hons), dC, CSCS
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