New Research Shows Knee Osteoarthritis Prevalence Is Rising

Dr. Felson, a co-author who has expertise in OA clinical research, emphasizes, however, that despite controlling for BMI in the study, he believes weight remains an important risk factor.

“Earlier populations were really much thinner than our more recent and current populations,” he says. “I think weight is still an important factor [because] obesity is such a big risk factor for arthritis. I think it does probably explain some of the increase in prevalence even though we tried to adjust for that.”

However, Dr. Felson acknowledges the study raises important questions about other possible risk factors that remain largely unrecognized. The study paid close attention to one in particular: physical activity.

Physical Activity & Knee OA

Although the study did not look at physical activity or other potential risk factors, the finding that the prevalence of knee OA has doubled since early times even after controlling for BMI and age allowed the authors to hypothesize that perhaps physical activity is a risk factor.

“Our data suggest that rather than physical activity being bad for our joints, it actually may be good, particularly during the growing years when a person is developing cartilage and bone,” says Dr. Wallace.

Dr. Callahan

According to Dr. Wallace, although the common assumption is that knee OA is related to wear and tear of the joint (through age and weight), the study results suggest the opposite is possible. “If knee OA is simply a matter of wearing out your joints, then we’d expect the prevalence would have been going down since World War II because, if anything, physical activity declined in the 20th century,” he says. “So it doesn’t make sense that knee OA is solely due to wear and tear when the prevalence is going up at the same time that people are getting more sedentary.”

Dr. Felson agrees physical activity is part of the picture, but cautions that physical activity has lots of complicated effects on knee OA. “We don’t know anything about the different levels or types of physical activity in these earlier populations,” he says. “We know individuals in the early industrial populations were often manual laborers and not recreational athletes and that manual laborers get more knee OA than people who are sedentary. But that is probably due to injuries they sustain at work, and that joint injury becomes knee OA later.”

Leigh F. Callahan, PhD, the Mary Link Briggs Distinguished Professor of Medicine, associate director at the Thurston Arthritis Research Center, and director of the Osteoarthritis Action Alliance at the University of North Carolina, Chapel Hill, wrote an editorial looking at research on physical activity and osteoarthritis.⁴ The article emphasized the limited evidence to date on the preventive effects of physical activity on knee OA. “Currently, there are no conclusive data one way or another regarding increased physical activity being protective for OA,” she says.