BOSTON—Exercise neither protects against nor increases the risk of knee osteoarthritis (OA) in older, overweight adults, according to study of 1279 subjects from the Framingham Offspring cohort that appears in the February 2007 issue of Arthritis Care &  Research.¹
 
David T. Felson, MD, MPH, of the Boston University School of Medicine, in Massachusetts, and colleagues report that prior physical activity (including walking, jogging, or other self-reported activity) did not increase the risk of developing knee OA over the course of a 9-year study. By comparing x-rays taken at baseline and at the end of the study, they also found that physical activity was not chondroprotective.

 "Walking for exercise and other recreational activities in older persons without knee OA do not affect these individuals' risk for developing OA, even if they are overweight," Dr. Felson concludes. In addition, "there is no measurable protective effect of recommended weight-bearing exercise on OA."

As a result of these findings, "physical activity can be done safely without concerns that persons will develop knee OA as a consequence," according to Dr. Felson.

Another study in the same issue of the journal seems to validate these findings by showing that regular sports activities are not related to the progression of knee OA.²

Study participants were questioned about their recent, regular physical activity, and underwent knee radiographs between 1 and 2 years later. They also answered questions about knee symptoms such as pain, aching, or stiffness and underwent a follow-up exam 9 years later that included knee x-rays and the same questions about symptoms; they were not questioned about physical activity at this follow-up. Using the Kellgren and Lawrence scale, researchers analyzed x-rays by looking at joint space loss, and they also examined symptoms. Participants were weighed initially and at follow-up.

Overweight patients did have an increased risk of developing OA, but physical activity did not mediate this risk, the study showed. Additionally, joint space loss was not affected by exercise, according to the radiographs.

In the second study, Janneke N. Belo, MD, MSc, of Erasmus Medical Center, in Rotterdam, The Netherlands, and colleagues reviewed 37 studies to determine predictive factors of the progression of knee OA. They found three studies showing no strong evidence that regular exercise was related to progression of knee OA. Sex, knee pain, quadriceps strength, and knee injury were not shown to be associated with progression either. Presence of generalized OA and the level of hyaluronic acid were, however, associated, according to this study.

New study supports current exercise recommendations

In an editorial accompanying the new studies,³ Marian A. Minor, PT, PhD, of the University of Missouri, in Columbia, calls Dr. Felson's study "a step toward evidence-based recommendations regarding exercise and the risk of knee OA."

The new study "supports recommending regular moderate physical activity without undue fear that such activity may increase the risk for knee OA," she notes. "In addition to improving the usefulness of knee OA research, our ultimate aim must be to produce evidence that assists clinical decision-making and individualized recommendations regarding safety and effectiveness of interventions, including physical activity."

First, do no harm

"There is no question about the benefits of regular physical activity from the standpoint of general health, life expectancy, well being, high blood pressure, and obesity," said Kenneth D. Brandt, MD, professor emeritus of medicine and orthopaedic surgery at Indiana University School of Medicine, in Indianapolis.

"Aerobic exercise has been shown in a number of studies to be beneficial for knee OA from a symptom standpoint," he said. "It decreases pain, and the question of whether it may be harmful or helpful relates in part to weakness around the quadriceps, which some have suggested may be a risk factor for development of knee OA," Dr. Brandt told CIAOMed.

"Exercise doesn't make it better or worse for the knee," he said. "The benefits of conditioning and fitness are overwhelming and that's more important then knee pain," he added. "Physical activity doesn't aggravate your arthritis, so you should exercise for general health. The vast majority of patients with knee OA can exercise, exercise safely, and feel better without harming the knee,"
Dr. Felson's new study does have limitations, he pointed out. For example, there was no magnetic resonance imaging exam at baseline, and participants were only asked about physical activity at the study's inception so there was no way to determine what their habits were 9 years later.

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References

1. Felson DT, Niu J, Clancy M, et al. Effect of recreational physical activities on the development of knee osteoarthritis in older adults of different weights: the Framingham Study. Arthritis Care Res. 2007;57:000-000.
2. Belo JN, Berger MY, Reijman M, et al. Prognostic factors of progression of osteoarthritis of the knee: systematic review of observational studies. Arthritis Care Res. 2007;57:000-000.
3. Minor MM. Physical activity and knee osteoarthritis: answers and questions. Arthritis Care Res. 2007;57:000-000.