• Stephen P Messier, David J Gutekunst, Cralen Davis, and Paul DeVita.
• Snow Biomechanics Laboratory, Department of Health and Exercise Science, Wake Forest University, Winston-Salem, North Carolina 27109, USA. messier@wfu.edu
• Arthritis Rheum. 2005 Jul 1; 52 (7): 2026-32.

ObjectiveTo 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.MethodsData 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).ResultsThere 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 9.8 N (1 kg) was associated with reductions of 40.6 N and 38.7 N in compressive and resultant forces, respectively. Thus, each weight-loss unit was associated with an approximately 4-unit reduction in knee-joint forces. In addition, a reduction in body weight of 9.8 N (1 kg) was associated with a 1.4% reduction (0.496 Nm) in knee abduction moment.ConclusionOur 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.

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