Clinical Context

Among older adults, knee osteoarthritis (OA) is the leading cause of functional limitation, such as difficulty walking and climbing stairs. To reduce these functional limitations, clinicians recommend physical activity.

However, it is unclear whether walking, as opposed to other physical activities, can protect against development of functional limitation in patients with knee OA. The goal of this study by White and colleagues was to evaluate the association of daily walking, measured in number of steps, with incident functional limitation 2 years later in people with or at risk for knee OA.

Study Synopsis and Perspective

Patients with knee OA can gain significant benefits and avoid physical function limitations by simply walking more, Daniel K. White, PT, ScD, and colleagues report in Arthritis Care & Research.

"As clinicians, we should be promoting walking in our patients with knee OA. We should have them measure their physical activity with a pedometer, much like people measure their weight with a scale. Those starting on a walking program should get to a target of at least 3000 steps/day and ultimately try to reach 6000 steps/day. This is well below the popular anecdote of 10,000 steps/day, which may be good news to those starting out. It doesn't take much to get to 3000 steps/day," Dr. White told Medscape Medical News. He is research assistant professor, Department of Physical Therapy & Athletic Training, Boston University College of Health and Rehabilitation Sciences, Massachusetts.

Long-Term Study Documents Benefits of Walking in Patients With Knee OA

The researchers measured daily steps taken by 1788 people with or at risk for knee OA who were part of the Multicenter Osteoarthritis Study, a large multicenter longitudinal cohort study of community-dwelling adults. Mean age was 67 years, mean body mass index was 31 kg/m², and 60% of participants were women.

The researchers measured the number of steps patients walked with an ankle monitor for 7 days. They measured functional limitation at baseline and again 2 years later. The researchers defined functional limitation as a walking speed of less than 1.0 m/s or Western Ontario and McMaster Universities Arthritis Index (WOMAC) physical function score of 28 or greater out of 68.

The authors reported, "Among study participants who did not develop slow walking at the two-year follow-up (<1.0 m/s), 80% walked at least 5300 steps/day." The minimum for preventing functional decline was between 3250 and 3700 steps/day. Walking an additional 1000 steps each day was associated with a 16% to 18% reduction in incident functional limitation 2 years later.

"Our findings add to [the] notion that walking is good for people with knee OA. Specifically, walking that occurs during unstructured activities, a few steps here and there, add up and do seem to make a difference in terms of prevention of functional limitation in this patient population. I hope that these findings will lead to clinicians encouraging their patients to use a pedometer to measure their physical activity and work towards the 3000 then 6000 steps/day goal," Dr. White said.

Results Mirror Those of Preclinical OA Studies

Giuseppe Musumeci, PhD, research professor of human anatomy, Department of Bio-Medical Science, University of Catania, Italy, told Medscape Medical News that the result from Dr. White and colleagues' study mirror those his team observed using rat models of knee OA. Dr. Musumeci was not involved in the current study.

"Although the diagnosis of OA was only based on radiologic and clinical features, and the use of StepWatch Activity Monitor could have some limitations, I think that the results are reliable, since they mirror the molecular and histopathologic findings. Unstructured physical activity is an easy and affordable way treat OA, especially for older patients, in whom comorbidity and metabolic diseases are also common. Structured physical activity adapted to age, OA, and comorbidity also could be helpful. Physical activity stimulates the expression of lubricin, a lubricant molecule of synovial fluid that is important for cartilage trophism and that contributes to the delay of OA development," Dr. Musumeci said.

More Walking Might Reduce Healthcare Costs Associated With Knee OA

According to Dr. White, data from the National Health and Nutrition Examination Survey showed that 80% of patients with OA have some limitation in movement and that 11% of adults with knee OA need assistance with personal care.

"Our findings strongly suggest that walking does work to prevent the onset of problems with physical functioning in the future in people with knee osteoarthritis," Dr. White said.

Dorothy D. Dunlop, PhD, professor of medicine and preventive medicine at Northwestern University Feinberg School of Medicine, Chicago, Illinois, said, "This paper provides additional evidence of benefits from being physically active for adults with arthritis. A key finding is that the more these adults walked, the smaller was the chance for subsequent functional problems. The benefit from walking demonstrated by this paper is good news, since walking is easy to weave into daily routines and has no cost." Dr. Dunlop was not involved in the study.

The authors concluded, "Clinicians and policy makers can consider these goals as preliminary levels of physical activity to recommend to people with or at high risk of knee OA. These steps/day thresholds merit further evaluation as improving daily walking may be an inexpensive means of minimizing functional limitations in knee OA."

"The public health message is adults should be as physically active as possible, including people with arthritis," Dr. Dunlop told Medscape Medical News. "This paper provides additional evidence of benefits from being physically active for adults with arthritis. A key finding is the more these adults walked, the smaller was the chance for subsequent functional problems. Even an increase as small as 1000 steps/day reduced the chance for developing functional problems."

Dr. Musumeci added, "I think that we can suggest to our patients to improve their physical activity, and 6000 steps/day could be a good goal. Preventing and delaying OA development could definitely reduce the cost of hospitalization and surgical intervention."

The authors, Dr. Musumeci, and Dr. Dunlop have disclosed no relevant financial relationships.

Arthritis Care Res. Published online June 12, 2014. Abstract

Clinical Implications

• In a prospective cohort study, more walking was associated with less risk for functional limitation from knee OA during a 2-year period.
• The findings of this prospective cohort study suggest that clinicians should promote walking in patients with knee OA and measurement of physical activity with use of a pedometer.

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