Osteoarthritis, or OA as it is commonly called, is the most common joint disease affecting middle-age and older people. It is characterized by progressive damage to the joint cartilage-the cushioning material at the end of long bones-and causes changes in the structures around the joint. These changes can include fluid accumulation, bony overgrowth, and loosening and weakness of muscles and tendons, all of which may limit movement and cause pain and swelling.
Knee osteoarthritis is a common form of osteoarthritis and is caused by cartilage breakdown in the knee joint. Factors that increase the risk of knee osteoarthritis include being overweight, age, injury or stress to the joints, and family history.
Researchers at Northwestern University and Feinberg School of Medicine in Chicago, Il, the University of Pittsburgh, and Brown University in Providence, R.I., analyzed data on physical activity levels in adults with or at risk for knee OA and their quality of life measurements using results from the Osteoarthritis Initiative (called OAI), a nationwide research study sponsored by the National Institutes of Health. The OAI includes questionnaire, laboratory tests and imaging results from more than 4,700 adults with or at risk for knee OA. The researchers wanted to determine if increased physical activity in OA patients would correlate to better Quality-Adjusted Life Years, or QALYs. QALYs are a measure of health outcomes based on both quality of life and survival duration a particular medical intervention would add to the patient's life. Cost effectiveness for any treatment can then be determined by the cost needed to improve QALYs by one.
"Because physical activity conveys many health benefits, the Department of Health and Human Services published physical activity guidelines in 2008 for all Americans including those with osteoarthritis," explains Kai Sun, MD; medical resident and research trainee; Northwestern Feinberg School of Medicine; and lead investigator in the study. "The guidelines recommend 150 minutes of moderate to vigorous activity a week performed in bouts lasting at least 10 minutes. The objective of our study was to investigate if meeting the 2008 DHHS physical activity guidelines translated into better QALYs among adults with or at risk for knee OA, and to postulate whether interventions to increase physical activity could be cost effective."
Physical activity levels in these participants were measured for one week using accelerometers, and participants fell into three groups: those meeting national physical activity guidelines, insufficiently active, and inactive. Participants meeting guidelines had 150 or more minutes per week of moderate to vigorous physical activity in bouts of 10 or more minutes. Participants who were insufficiently active had some moderate to vigorous activity, but less than 150 minutes per week, and inactive participants had no bouts of moderate to vigorous activity lasting more than 10 minutes per week. Data were stratified by gender and body-mass index. Various socioeconomic and health factors like smoking, age, education levels, co-existing diseases, and knee OA symptoms were also taken into account. Physical activity was monitored at the beginning of the study (OAI 48-month follow-up visit). Health-related utility scores used to calculate QALYs were measured at the beginning of the study and then again two years later (OAI 72-month follow-up visit).
The researchers found a significant graded relationship between higher levels of physical activity and QALYs. Over the course of two years, those who met physical activity guidelines had QALYs that were 0.11 higher than those who were inactive, and even those who were insufficiently active had QALYs that were 0.058 higher than those who were inactive after adjusting for socioeconomic and health factors. These numbers represent about 10 to 20 additional days of perfect health over a year. Interventions to encourage adults to increase their physical activity level even if guidelines are not fully met could potentially translate to better quality of life, added years of healthy life, and thereby lower overall health care costs, the study's authors concluded. They estimated that medical intervention costing $1,450 or less that resulted in increased moderate to vigorous physical activity in those with or at risk for knee OA would be cost-effective, using a $50,000 cut-off for additional cost per QALYs gained.
"Regular physical activity improves health and reduces mortality in the general population. Furthermore, physical activity promotes arthritis-specific health benefits including improving symptoms, function and psychosocial outcomes, as well as reduced disability," says Dr. Sun. "Despite these benefits, the majority of adults in the U.S. do not attain the recommended amounts of physical activity. The costs associated with the treatment of inactivity-related diseases and injuries, lost productivity and diminished quality of life poses an economic burden. Therefore, promoting physical activity is an important component in promoting overall health, addressing the epidemic of obesity and other chronic illnesses, and reducing health care costs in the long term."