Weight loss reduces knee‐joint loads in overweight and obese older adults with knee osteoarthritis

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Abstract
Objective: To determine the relationship between change in body mass and knee‐joint moments and forces during walking in overweight and obese older adults with knee osteoarthritis (OA) following an 18‐month clinical trial of diet and exercise.Methods: Data were obtained from 142 sedentary, overweight, and obese older adults with self‐reported disability and radiographic evidence of knee OA who underwent 3‐dimensional gait analysis. Gait kinetic outcome variables included peak knee‐joint forces and peak internal knee‐joint moments. Mixed regression models were created to predict followup kinetic values, using followup body mass as the primary explanatory variable. Baseline body mass was used as a covariate, and thus followup body mass was a surrogate measure for change in body mass (i.e., weight loss).Results: There was a significant direct association between followup body mass and peak followup values of compressive force (P = 0.001), resultant force (P = 0.002), abduction moment (P = 0.03), and medial rotation moment (P = 0.02). A weight reduction of 9.8N (1 kg) was associated with reductions of 40.6N and 38.7N in compressive and resultant forces, respectively. Thus, each weight‐loss unit was associated with an ∼4‐unit reduction in knee‐joint forces. In addition, a reduction in body weight of 9.8N (1 kg) was associated with a 1.4% reduction (0.496 Nm) in knee abduction moment.Conclusion: Our results indicate that each pound of weight lost will result in a 4‐fold reduction in the load exerted on the knee per step during daily activities. Accumulated over thousands of steps per day, a reduction of this magnitude would appear to be clinically meaningful.