Regular physical activity may strenghten knee cartilage

Osteoarthritis (OA) is the leading cause of disability among adults. As the population ages, increased intervention efforts are vital to controlling the individual and public health toll of this chronic, crippling joint disease. Along with early diagnosis, moderate exercise is one of the most effective ways to reduce pain and improve function in patients with OA of the knee and hip. Yet, more than 60 percent of U.S. adults with arthritis fail to meet the minimum recommendations for physical activity.

Based on the "wear and tear" nature of OA, the commonly held belief is that exercise will not strengthen joint cartilage and may even aggravate cartilage loss. Until recently, investigators were unable to put that belief to the test. Radiographs, the standard measure of OA's progression, made it impossible to assess cartilage before severe cartilage damage had occurred. Advances in magnetic resonance imaging (MRI) now make it possible to study cartilage changes earlier in the course of OA. Two researchers in Sweden, Leif Dahlberg, M.D., Ph.D., and Ewa M. Roos, P.T., Ph.D., used a novel MRI technique to determine the impact of moderate exercise on the knee cartilage of subjects at high risk for developing OA--middle-aged men and women with a history of surgery for a degenerative meniscus tear. In the November 2005 issue of Arthritis & Rheumatism (http://www.interscience.wiley.com/journal/arthritis), they share evidence to support the therapeutic value of exercise for OA patients, for improving not only joint symptoms and function, but also the quality of knee cartilage.

Working with the Department of Orthopedics at Malm� and Lund University Hospitals and the medical faculty of Lund University, Drs. Dahlberg and Roos recruited 29 men and 16 women, between the ages of 35 and 50, who had undergone meniscus repair within the past 3 to 5 years. Subjects were randomly assigned to either an exercise group or a control group. The exercise group was enrolled in a supervised program of aerobic and weight-bearing moves, for 1 hour, 3 times weekly for 4 months. At the study's onset and follow-up, subjects from both groups underwent MRI scans to evaluate knee cartilage. The technique used focused specifically on the cartilage's glycosaminoglycan (GAG) content, a key component of cartilage strength and elasticity. Subjects also answered a series of questions about their knee pain and stiffness, as well as their general activity level. Of the original 45 subjects, 30--16 in the exercise group and 14 in the control group--completed the trial and all post-trial assessments.

In the exercise group, many subjects reported gains in physical activity and functional performance tests compared with subjects in the control group. Improvements in tests of aerobic capacity and stamina affirmed the self-reported changes. What's more, MRI measures of the GAG content showed a strong correlation with the increased physical training of the subjects who had regularly participated in moderate, supervised exercise.

"This study shows compositional changes in adult joint cartilage as a result of increased exercise, which confirms the observations made in prior animal studies but has not been previously shown in humans," notes Dr. Dahlberg. "The changes imply that human cartilage responds to physiologic loading in a way similar to that exhibited by muscle and bone, and that previously established positive symptomatic effects of exercise in patients with OA may occur in parallel or even be caused by improved cartilage properties."

As Drs. Dahlberg and Roos acknowledge, the study does have limitations--its small sample size and narrow focus on meniscectomized knee joints--and makes no claims for predicting the long-term effects of exercise on cartilage. The conclusion, however, remains worthy of serious consideration: "Exercise may have important implications for disease prevention in patients at risk of developing knee OA."