Changes in knee biomechanics after a hip-abductor strengthening protocol for runners with patellofemoral pain syndrome.

CONTEXT Very few authors have investigated the relationship between hip-abductor muscle strength and frontal-plane knee mechanics during running. OBJECTIVE To investigate this relationship using a 3-week hip-abductor muscle-strengthening program to identify changes in strength, pain, and biomechanics in runners with patellofemoral pain syndrome (PFPS). DESIGN Cohort study. SETTING University-based clinical research laboratory. PATIENTS OR OTHER PARTICIPANTS Fifteen individuals (5 men, 10 women) with PFPS and 10 individuals without PFPS (4 men, 6 women) participated. INTERVENTION(S) The patients with PFPS completed a 3-week hip-abductor strengthening protocol; control participants did not. MAIN OUTCOME MEASURE(S) The dependent variables of interest were maximal isometric hip-abductor muscle strength, 2-dimensional peak knee genu valgum angle, and stride-to-stride knee-joint variability. All measures were recorded at baseline and 3 weeks later. Between-groups differences were compared using repeated-measures analyses of variance. RESULTS At baseline, the PFPS group exhibited reduced strength, no difference in peak genu valgum angle, and increased stride-to-stride knee-joint variability compared with the control group. After the 3-week protocol, the PFPS group demonstrated increased strength, less pain, no change in peak genu valgum angle, and reduced stride-to-stride knee-joint variability compared with baseline. CONCLUSIONS A 3-week hip-abductor muscle-strengthening protocol was effective in increasing muscle strength and decreasing pain and stride-to-stride knee-joint variability in individuals with PFPS. However, concomitant changes in peak knee genu valgum angle were not observed.