Hip and knee frontal plane biomechanics in people with medial compartment knee osteoarthritis
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Objectives: To investigate differences between hip abductor muscle strength, hip and knee adduction moments and knee joint alignment in people with moderate/severe and mild medial compartment knee osteoarthritis (OA), and people without OA, and identify variables explaining variance in knee adduction moment in participants with OA. Background: It has been suggested that weakness of hip abductor muscles may lead to displacement of the centre of mass of body away from the stance limb during gait, resulting in increased knee adduction moment, a predictor of disease progression. Methods: Participants with medial compartment knee OA were divided into moderate/severe (n=23) and mild OA groups (n=15) based on radiographic grading. Control subjects were recruited to match participants in the moderate/severe group for age and gender (n=23). Hip abductor and adductor muscle isometric strength was measured using the Biodex dynamometer. Gait speed and hip and knee peak adduction moments and percentage of the stance phase where these occurred were obtained using a three dimensional motion analysis system and two force platforms. Knee alignment and severity of OA were measured from radiographs. Statistics: Univariate analysis of variance (ANOVA) was performed to determine group differences. Stepwise linear regression analysis was performed to identify the variables which contribute to variation in knee adduction moment. Results: Moderate/severe OA group participants had higher body mass index (BMI) than the mild OA and control group (p=0.01) and greater varus alignment compared to the control group (p<0.01). There was no difference between the mean hip abductor and adductor muscle strength and hip and knee adduction moments among the three groups. Peak hip (p=0.02) and knee adduction moments (p<0.05) occurred later in stance phase of gait in the moderate/severe OA group as compared to control group. Knee joint alignment (26%), hip abductor muscle isometric strength (20%), gait speed (16%) and hip adduction moment (11%) explained 73% of variance in the knee adduction moment in the participants with OA. Conclusion: Findings from this study do not support the theory that weakness of the hip abductor muscles contributes to higher knee adduction moments.