Patellofemoral Pain Syndrome and Pain Severity Is Associated With Asymmetry of Gluteus Medius Muscle Activation Measured Via Ultrasound
OBJECTIVE: The aim of the study was to determine whether gluteus medius muscle thickness or activation differed between left and right sides and was associated with patellofemoral pain presence or severity. DESIGN: Males and females were recruited and screened by a physiotherapist for inclusion in the control or patellofemoral pain syndrome group. Bilateral measures were obtained for Q angle and gluteus medius muscle thickness at rest and on contraction via standing hip external rotation, using ultrasound. Muscle activation was calculated as the percentage change in muscle thickness on contraction relative to at rest. Patellofemoral pain syndrome participants completed the anterior knee pain scale and a visual analog pain scale. RESULTS: Gluteus medius muscle thickness at rest and on contraction, muscle activation, and Q angle were not different between control (n = 27, 63% female) and patellofemoral pain syndrome (n = 27, 59% female) groups. However, patellofemoral pain syndrome participants had a significantly larger left-right side imbalance in gluteus medius muscle activation than controls (15.9 ± 19.3% vs. 4.4 ± 21.9%, P < 0.05). Among patellofemoral pain syndrome participants, the magnitude of asymmetry of gluteus medius muscle activation was correlated with knee pain score (r = 0.425, P = 0.027). CONCLUSIONS: Asymmetry of gluteus medius muscle activation was associated with patellofemoral pain syndrome and pain severity. This is clinically relevant for patellofemoral pain syndrome prevention and treatment, particularly because this was quantifiable using ultrasound.