Weight loss results in fourfold reduction of knee stress in OA patients

Beth Kapes

July 22, 2005

July 22, 2005

Winston-Salem, NC - With every pound of weight lost, there is a direct correlation in the reduction of pressure exerted on the knee per step during daily activities in overweight and obese older adults with knee osteoarthritis (OA) [ 1 ]. New data by US researchers, reported in the July 2005 issue of Arthritis & Rheumatism, show that in adults with knee OA who averaged a body weight loss of 5%, every pound netted a 4-lb reduction in pressure exerted on the knee and an 18% improvement in function.

"It seems intuitive that if you lose weight, the stress on your knees will be less, but it's never been proven. What surprised us was the potential benefit you get from every unit of weight lost," says lead researcher Dr Stephen Messier (Wake Forest University, Winston-Salem, NC). "This is another piece of the puzzle saying that moderate exercise and modest weight loss really has a positive effect on function and pain, and we now know it has an impact on the stress of the joint as well."


Weight loss beneficial

The researchers were inspired to conduct the current study by the results of the Arthritis, Diet, and Activity Promotion Trial (ADAPT) [2], also headed by Messier. That study, conducted in 316 overweight and obese, sedentary older adults with knee OA, proved that moderate weight loss combined with exercise offered the most benefit, with function improving 24% and with a significant improvement in mobility, as previously reported by rheuma wire . "While the ADAPT study looked at each entity separately, including exercise, weight loss, and the combination of the two, it was clear that the diet-and-exercise group performed best over the 18-month period," Messier says.

Messier et al's current study explored the relationship between change in body weight and change in knee-joint loads during gait in an attempt to clarify the pathophysiologic processes involved.

"Weight loss causes changes in many internal mechanics—we know it has an effect on function and pain, but now we'd like to find out why," Messier says. "We have preliminary data from this same study that also show a decrease in inflammation [as a result of weight loss], but is this the part of the mechanism that causes OA?"


Study completes gait analysis to prove theory

Messier et al investigated a subset of 142 subjects from the original 316 who participated in ADAPT. The sedentary, overweight, and obese older adults with symptomatic knee OA underwent biomechanics testing similar to that in ADAPT.

Study participants were tested at baseline and at six-month and 18-month follow-up visits. By using the Lafayette Model 63501 photoelectric control system (Lafayette Instrument Co, IN), they walked a 7.3-meter course six times with a freely chosen walking speed in an identical make and model of athletic shoe. The primary outcomes were the peak values of nine knee-joint kinetic variables, comprising compressive, anteroposterior shear, and resultant forces, and peak values of six internal knee moments, comprising flexion, extension, abduction, adduction, medial rotation, and lateral rotation, the authors note.

Of the 142 participants, baseline complete data on biomechanics were obtained from 134 (94%); 116 had complete data from at least one biomechanics follow-up visit (either six and/or 18 months). The mean ¿ SEM body mass and body mass index (BMI) of the cohort at baseline were 93.2¿1.3 kg and 34.0¿0.4 kg/m ¿, respectively, with mean ¿ SEM values at follow-up being 90.8¿1.4 kg and 33.0¿0.4 kg/m ¿, respectively. The study subjects lost 2.6% of their body mass and lowered their BMI by 3.0%.

The significant relationship between weight loss and reduction in compressive knee-joint loads indicates that the force reduction was larger than the actual weight reduction, the researchers comment. Results showed a significant direct association between follow-up body mass and peak follow-up values of compressive force (p=0.001), resultant force (p=0.002), abduction moment (p=0.03), and medial-rotation moment (p=0.02).

Weight reduction of 9.8 N (1 kg) caused reductions of 40.6 N and 38.7 N in compressive and resultant forces, with each weight-loss unit equaling a ~4-unit reduction in knee-joint forces. The same amount of weight loss also caused 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 researchers conclude. "Accumulated over thousands of steps per day, a reduction of this magnitude would appear to be clinically meaningful."


But does it lead to a slowing of the disease process?

"Our studies prove that modest weight loss and moderate exercise should be the cornerstone for treatment [of OA of the knee]," Messier tells rheuma wire .

"What we're very encouraged with is that these noninvasive ways of treating knee OA are proving to be effective. This has become even more important over the past year due to the recent evidence linking [nonsteroidal anti-inflammatory drugs] to an increased risk of heart disease," says Messier.

"The one discouraging point is that no intervention that we are aware of, including our own, has shown to decrease or halt the disease process," Messier points out. "While this study accomplished only a 5% weight loss, we're thinking that if you can achieve a more intensive weight loss, there will be a greater decline in inflammation and stress on the knee joint, and this may lead to a slowing of the disease process and the survival of cartilage."


Sources

  1. Messier SP, Gutekunst DJ, Davis C, DeVita P. Weight loss reduces knee-joint loads in overweight and obese older adults with knee osteoarthritis. Arthritis Rheum 2005; 52: 2026-32.

  2. Messier SP, Loeser RF, Miller GD, et al. Exercise and dietary weight loss in obese older adults with knee osteoarthritis; the Arthritis, Diet, and Activity Promotion Trial. Arthritis Rheum 2004; 50: 1501-10.

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