A long-term study of the effects of weight loss on knee osteoarthritis in overweight and obese patients suggests that losing a pound results in a 4-pound reduction in knee-joint load for each step.

Osteoarthritis, a complex, degenerative joint disease with several established risk factors, is the leading cause of disability in the United States. For osteoarthritis of the knee, the most important modifiable risk factor is obesity. Weight loss and exercise to reduce the painful and incapacitating symptoms of knee osteoarthritis is recommended by both the American College of Rheumatology and the European League Against Rheumatism.

The researchers set out to investigate the specific, direct relationship between weight loss and knee-joint stress while walking. Their findings indicate that moderate weight loss results in knee-joint load reduction of a cumulative amount with considerable clinical implications.

Conducted over an 18-month period, the study focused on 142 overweight and obese adults with radiographic evidence of knee osteoarthritis. Ranging in age from 60 to 89, the subjects were mostly female (74 percent) and white (75 percent); all were considered sedentary. Each subject's weight and body mass index (BMI), as well as scores on standard scales of function and pain, were obtained at baseline (start of study) and again at 6-months and at 18-months. At baseline and both follow-up visits, each subject also underwent gait analysis and a battery of biomechanical tests to assess changes in knee-joint forces, both compressive and resultant, and moments, both abduction and rotation. Over the course of the study, all participants followed a prescribed weight loss plan, some through diet only, some through exercise only, and some through a combination of healthy living habits.

At the study's culmination, participants experienced average weight loss of 2 percent and lowered their BMI by 3 percent. After adjusting for baseline body mass and baseline knee-joint force, researchers found a significant association between weight loss and reduction in compressive knee-joint loads. In fact, the force reduction was 4-times greater than the actual weight reduction. In other words, their findings indicated that, for every 1 pound of weight lost, there is a 4-pound reduction in the load exerted on the knee for each step taken during daily activities.

"The accumulated reduction in knee load for a 1-pound loss in weight would be more than 4,800 pounds per mile walked," notes Stephen P. Messier, the leading author of the study. "For people losing 10 pounds, each knee would be subjected to 48,000 pounds less in compressive load per mile walked. Although there are no longitudinal studies indicating that weight loss in humans slows the progression of knee osteoarthritis, a reduction of this magnitude would appear to be clinically relevant."

Supporting the positive impact of weight loss on knee osteoarthritis, this compelling study suggests the need for further research into the potential of weight loss, whether achieved through diet alone or in tandem with exercise, to slow, and perhaps even prevent, the crippling outcome of osteoarthritis.
References:
1. Stephen P. Messier, et al. Weight Loss Reduces Knee-Joint Loads in Overweight and Obese Older Adults With Knee Osteoarthritis. Arthritis & Rheumatism, Volume 52 Issue 7, Pages 2026 - 2032. DOI 10.1002/art.21139.