Differences in Hip Kinematics, Muscle Strength, and Muscle Activation Between Subjects With and Without Patellofemoral Pain

STUDY DESIGN: Controlled laboratory study using a cross-sectional design. OBJECTIVES: To determine whether females with patellofemoral pain (PFP) demonstrate differences in hip kinematics, hip muscle strength, and hip muscle activation patterns when compared to pain-free controls. BACKGROUND: It has been proposed that abnormal hip kinematics may contribute to the development of PFP. However, research linking hip function to PFP remains limited. METHODS AND MEASURES: Twenty-one females with PFP and 20 pain-free controls participated in this study. Hip kinematics and activity level of hip musculature were obtained during running, a drop jump, and a step-down maneuver. Isometric hip muscle torque production was quantified using a multimodal dynamometer. Group differences were assessed across tasks using mixed-design 2-way analyses of variance and independent t tests. RESULTS: When averaged across all 3 activities, females with PFP demonstrated greater peak hip internal rotation compared to the control group (mean +/- SD, 7.6 degrees +/- 7.0 degrees versus 1.2 degrees +/- 3.8 degrees; P<.05). The individuals in the PFP group also exhibited diminished hip torque production compared to the control group (14% less hip abductor strength and 17% less hip extensor strength). Significantly greater gluteus maximus recruitment was observed for individuals in the PFP group during running and the step-down task. CONCLUSION: The increased peak hip internal rotation motion observed for females in the PFP group was accompanied by decreased hip muscle strength. The increased activation of the gluteus maximus in individuals with PFP suggests that these subjects were attempting to recruit a weakened muscle, perhaps in an effort to stabilize the hip joint. Our results support the proposed link between abnormal hip function and PFP.