Each Pound of Weight Lost May Reduce Knee Load per Step Fourfold

Laurie Barclay, MD

July 01, 2005

July 1, 2005 — For each pound of weight lost, the knee will experience a fourfold reduction in load during daily activities, according to the results of a study published in the July issue of Arthritis & Rheumatism. The authors suggest that this may be clinically meaningful in overweight and obese older adults with knee osteoarthritis (OA).

"The most important modifiable risk factor for the development and progression of OA is obesity," write Stephen P. Messier, PhD, from Wake Forest University in Winston-Salem, North Carolina, and colleagues. "Weight loss reduces the risk of symptomatic knee OA, and for obese patients with knee OA, weight loss and exercise are recommended by both the American College of Rheumatology and the European League Against Rheumatism."

Following an 18-month clinical trial of diet and exercise, 142 sedentary, overweight, and obese older adults with radiographic evidence of knee OA were evaluated to determine the relationship between weight loss and knee-joint forces during walking. Three-dimensional gait analysis determined peak knee-joint forces and peak internal knee-joint moments.

Follow-up body mass was directly associated with peak follow-up values of compressive force ( P = .001), resultant force ( P = .002), abduction moment ( P = .03), and medial rotation moment ( P = .02). Weight reduction of 9.8 N (1 kg) was associated with reductions of 40.6 N in compressive forces and of 38.7 N in resultant forces. Each weight-loss unit was therefore associated with an approximately four-unit reduction in knee-joint forces, and 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.

"Our results indicate that each pound of weight lost will result in a fourfold reduction in the load exerted on the knee per step during daily activities," the authors write. "Accumulated over thousands of steps per day, a reduction of this magnitude would appear to be clinically meaningful."

The authors suggest that weight loss may improve subtalar motion and reduce demand on proximal muscles to provide stability.

"A critical question that remains is whether this relationship holds true in an experimental longitudinal study, and whether such an approach results in a slowing of disease progression," the authors conclude.

The National Institutes of Health supported this study.

Arthritis Rheum. 2005;52:2026-2032

Reviewed by Gary D. Vogin, MD

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