Purpose: Hip muscle weakness may result in impaired frontal plane pelvic control during gait, leading to greater medial compartment loading, as measured by the knee adduction moment, in persons with knee osteoarthritis (OA). The purpose of this study was to evaluate the influence of an 8-week home-based strengthening program for the hip abductor muscles on hip muscle strength and the external knee adduction moment during gait in individuals with medial knee OA compared to an asymptomatic control group. Secondary objectives were to determine if hip abductor strengthening exercises would improve physical function and knee symptoms in this sample of people with knee OA.

Method: Forty participants with knee OA were age and gender-matched with an asymptomatic control group. Three-dimensional gait analysis was performed to obtain peak knee adduction moments in the first 50% of stance phase. Isokinetic concentric strength of the hip abductor muscles was measured using a Biodex Isokinetic Dynamometer. Functional performance was evaluated using the Five-Times-Sit-to-Stand test. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) provided an assessment of knee pain. Following initial testing, participants with knee OA were instructed in a home program of hip abductor strengthening exercises. All participants were re-evaluated after 8 weeks.

Results: There was no significant difference in isokinetic hip abductor muscle strength between groups at baseline or at follow-up. An improvement in hip abductor strength occurred in the OA group following the intervention (p = 0.036). The OA group had higher peak knee adduction moments than the control group (p = 0.006), but there was no change in the knee adduction moment over time in either group (p > 0.05). The OA group performed the sit-to-stand test more slowly than the control group (p = 0.001). At final testing, functional performance on the sit-to-stand test had improved in the OA group compared to the control group (p = 0.021). The OA group showed a trend towards decreased knee pain (p = 0.05).

Conclusion: An 8-week home program of hip abductor muscle strengthening did not reduce knee joint loading, but improved function, in a group of participants with medial knee OA.