A novel magnetic resonance imaging (MRI) technique employed in a new study suggests that human articular cartilage is capable of adapting to physical load, and that modest exercise improves knee cartilage glycosaminoglycan (GAG) content in patients at risk for developing osteoarthritis (OA).

The new findings, which appear in the November 2005 issue of Arthritis & Rheumatism,¹ demonstrate for the first time in humans that moderate levels of physical activity can lead to improvements in GAG content.

"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," conclude Leif Dahlberg, MD, PhD, an orthopaedist at Malmö University Hospital, and Ewa M. Roos, PT, PhD, of Lund University, both in Sweden.

Along with improving GAG content, exercise also improved joint pain and symptoms, the study showed.

The Swedish researchers looked at the effects of 4 months of moderate exercise on the knee cartilage of 29 men and 16 women aged 35 to 50 who had undergone meniscus repair within the past 3 to 5 years. The exercise group was enrolled in a supervised program of aerobic and weight-bearing exercise for 1 hour, three times a week, for 4 months. No intervention was used in the control group.

At baseline and follow-up, subjects from both groups underwent MRI scans to evaluate knee cartilage. The technique used focused specifically on GAG content. Patients also answered questions about their knee pain and stiffness and general activity level.           

In the exercise group, many patients showed gains in physical activity and functional performance tests compared with their counterparts in the control group. These improvements were affirmed by self-reported changes. MRI measures of patients' GAG content showed a strong correlation between improved GAG levels and the increased physical training in the exercise group.

"Moderate, supervised exercise improves knee-cartilage GAG content in patients at risk of OA [and] improvements in pain and function are observed in parallel with [this] structural improvement," the study authors write. "Exercise may have important implications for disease prevention in patients at risk of developing knee OA."

Study limited by MRI readings, without direct measurements

"This is an interesting article that has good, supportive findings as to the chemical and scientific basis for why we support exercise to help people with arthritis," says Brian Donley, MD, vice chairman of the department of orthopaedic surgery at the Cleveland Clinic Foundation in Cleveland, Ohio.

Dr. Donley points out however that the new study does have some limitations, including the small sample size. "The actual GAG findings are all inferred from MRI readings, as opposed to a direct measurement," he says. "Nonetheless, it's a nice step forward to show some basic science supporting why exercise helps people with arthritis."

Reference

1. Roos EM, Dahlberg L. Positive effects of moderate exercise on glycosaminoglycan content in knee cartilage: a four-month, randomized, controlled trial in patients at risk of osteoarthritis. Arthritis Rheum. 2005;52:3507-3514.