The influence of hip abductor muscle performance on dynamic postural stability in females with patellofemoral pain.

Hip abductors play an important role in maintaining trunk and pelvis stability during unipedal tasks. The purpose of the study was to compare postural stability between individuals with patellofemoral pain (PFP) and pain-free controls. A secondary purpose was to evaluate the effect of a hip stabilizing brace on postural stability. Twenty females with PFP (27.3±6.3 years) and 19 controls (26.1±4.5 years) participated. Each subject performed a unipedal step-down balance task with the stance leg on a force platform from which center of pressure (COP) excursion was recorded. Quantitative COP excursion patterns (mean and peak displacements) were used as measures of postural stability. For subjects with PFP, postural stability also was quantified following the application of a hip stabilizing brace. Hip abductor strength was significantly lower in PFP group compared to the control group (1.39±0.4 vs. 1.62±0.26 N/kg-BW, p=0.046). Peak and mean medial-lateral COP displacements during the balance task were greater in the PFP group (39.8±6.7 vs. 24.3±3.8 mm, p<0.001; 24.7±16.3 vs. 13.5±4.4 mm, p=0.005). Application of the hip stabilizing brace reduced the peak and mean COP displacement (39.8±6.7 vs. 24.7±4.7 mm, p<0.001; 24.7±16.3 vs. 16.8±15.1 mm, p=0.02). Our results demonstrate that females with PFP exhibit impaired medial-lateral postural stability when compared to control subjects. Application of a hip stabilizing brace significantly improved stability to a level comparable to the controls.