Effect of physical activities on knee osteoarthritis in older adults

Regular exercise is recommended for middle-aged and older people, but the effect of exercise on the development of osteoarthritis (OA) in older people is unclear, especially if they are overweight.

Some studies have suggested that exercise has a protective effect, but few studies have been conducted where patients are asked about physical activity and followed to find out what develops. Meanwhile, obesity is a major risk factor for knee OA, and the question has been raised as to whether weight-bearing activity may be harmful to people who are overweight. A new study published in the February 2007 issue of Arthritis Care & Research examined the effects of physical activity over a long period in older adults, many of whom were overweight, and found that exercise neither protects against nor increases the risk of knee OA.

Led by David T. Felson of the Boston University School of Medicine in Boston, MA, researchers conducted a study of 1,279 subjects from the Framingham Offspring cohort, which consists of the offspring of the original Framingham cohort. Persons were questioned about recent physical activity they had engaged in on a regular basis, and between one and two years later (1993-1994) had knee X-rays. They were also asked questions about knee symptoms such as pain, aching or stiffness. Between 2002 and 2005 they were called back for a follow-up exam, during which they underwent the same knee X-rays and were asked the same questions about symptoms, but not about physical activity. They were also weighed initially and at follow-up, when X-rays were read by a bone and joint radiologist and a rheumatologist.

Analysis of the results showed no relationship between recreational walking, jogging or other self-reported activity and the development of knee OA. Even though the overweight patients had an increased risk of developing OA, physical activity did not contribute to this risk. Also, despite previous studies that suggested that exercise may prevent joint space loss, the study did not find this to be the case. "This suggests that in middle-aged and older adults who do not have OA, exercise does not protect against disease development," the authors state.

The study attempted to examine all the ways in which OA might appear by looking at X-rays that indicated the development of structural disease using a well-known index (the Kellgren and Lawrence scale), by looking at joint space loss, which is thought to indicate cartilage loss, and also by examining symptoms. The authors conclude: "Physical activity can be done safely without concerns that persons will develop OA as a consequence."

In another study in the same issue, researchers led by J.N. Belo of Erasmus Medical Center in Rotterdam, Netherlands published an overview of 37 studies appearing up to December 2003 to determine predictive factors of the progression of knee OA. As was the case with the Felson study, they found three studies showing no strong evidence that regular exercise was related to progression of knee OA; Other studies found that sex, knee pain, quadriceps strength and knee injury were also not associated with progression of knee OA. On the other hand, the presence of generalized OA and the level of hyaluronic acid (a protein found in joints) were predictive of progression of the disease.

In an accompanying editorial in the current issue Marian A. Minor of the University of Missouri in Columbia, MO notes that the Felson study helps to clarify the understanding of the relationship between knee OA and physical activity by using precise definitions of OA, using valid methods to assess prior physical activity, and evaluating the true incidence of the disease by eliminating patients who showed evidence of it on X-rays taken when the study began. "Taken together, these methods result in a useful and valid study that supports recommending regular moderate physical activity without undue fear that such activity may increase the risk for knee OA," the author states. Since physical activity does not appear to increase the risk of knee OA, the author wonders what variables may possibly play a role in its development and progression. She suggests that many studies fail to collect data about knee OA, such as age at onset, occupational and medical history, and response to medication and physical therapy, that may shed some light on the disease. Noting that future research should identify variables relevant to knee OA that make a difference in individual response, the author concludes: "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."