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

Abstract

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.

Figures

Figure 1

Retroreflective marker placement used for kinematic data collection.

Figure 2

The 2 hip-abductor muscle-strengthening exercises performed by the patellofemoral pain syndrome group. A, B, In the first exercise, the patient moves the involved leg outward, keeping the knee straight. C, D, In the second exercise, the patient moves the involved leg back to a 45° angle, keeping the knee straight and the pelvis stable.

Figure 3

Representative example of reduced stride-to-stride knee-joint variability of movement patterns for a patient with patellofemoral pain syndrome before (A) and after (B) the 3-week rehabilitation protocol. The thin lines represent the 10 individual footfalls over the stance phase of running gait, and the thick, dark line is the ensemble average. Note how the overall patterns for the ensemble averages are similar, thus contributing to no measured differences in peak knee genu valgum angle.