Throughout the United States, the rate of knee replacement operations has surged in recent years. Experts have speculated that the increased prevalence of knee pain or of symptomatic knee osteoarthritis (OA) is due to an aging and increasingly obese U.S. population, which in turn may be the cause for the increase in knee surgeries. However, formal assessments of the secular trend of knee pain and symptomatic knee OA have been lacking.

In the Annals of Internal Medicine, David T. Felson, MD, MPH, and colleagues addressed this void when they conducted a study examining whether a change in the prevalence of knee pain and symptomatic OA could be attributed to age, BMI, and radiographic knee OA. “It’s largely unknown if the increase in knee replacements was due to patients seeking the procedure more often,” explains Dr. Felson. “We also don’t have a great deal of data on the trends in knee OA.”

Key Findings

For their study, Dr. Felson and colleagues collected data from six National Health and Nutrition Examination Surveys (NHANES) conducted between 1971 and 2004 and from three examination periods in the Framingham Osteoarthritis (FOA) study between 1983 and 2005. “We wanted to see if the prevalence of knee OA had increased over time,” Dr. Felson says. In all samples studied, the age-adjusted prevalence of knee pain and symptomatic knee OA increased substantially over time. Between 1974 and 1994, the prevalence of knee pain—with adjustment for age and BMI—increased by about 65% among Caucasian and Mexican men and women and among African-American women in NHANES (Figure 1). In FOA, the age and BMI-adjusted prevalence of knee pain and symptomatic knee OA approximately doubled in women and tripled in men over a 20-year period (Figure 2). Among those with radiographic OA, the prevalence of knee pain tripled in women and more than quadrupled in men during this period.


“We recognize that age and weight are both risk factors for knee OA,” says Dr. Felson, “but with the FOA data, the prevalence of knee OA still increased substantially, even after adjusting for both factors. This suggests that some of the increasing prevalence is not explained by the aging population and their increasing weight. It could be due to a higher tendency of patients having trouble with and reporting pain. Another factor may be that middle- and older-age patients are developing knee pain as a result of participating in athletic activities that they typically would not have engaged in previously.”

Important Implications

The increased prevalence of knee pain may translate into higher demand for knee replacement, but the subjects analyzed in the study by Dr. Felson and colleagues were not followed to the point of knee replacement. “Unfortunately, it’s a hard topic to study,” Dr. Felson explains. “Information on disease prevalence is required over multiple decades, and researchers must use the same definitions in order to test whether prevalence has changed over time. That is a daunting challenge, but one that we need to take so that we can get a better idea of the real prevalence of knee OA and then tie this information to specific factors.”

Dr. Felson says clinicians should recognize that knee OA is a condition that will be encountered more frequently in the coming years. “Because many of these patients require knee replacements—and these surgeries make up an enormous sum of healthcare spending—physicians should become increasingly familiar with the multiple treatment options that are available,” says Dr. Felson. “It would behoove us to determine what nonsurgical therapies are effective in relieving pain so that we can hopefully delay the need for knee replacement surgery. Unfortunately, many physicians tend to prescribe analgesics or anti-inflammatory drugs and hope for the best. It’s important to be more proactive and consider other potentially effective therapies in the spectrum of available treatment options for knee OA.”

To gain a better understanding of the available treatment options for knee OA, Dr. Felson recommends that clinicians use resources and guidelines from trusted organizations, such as the American Association of Orthopaedic Surgeons and the American College of Rheumatology. “These associations offer helpful information about non-pharmacologic and pharmacologic therapies,” he says. “They’re a good starting point, but clinicians should remember that each patient is unique and will need to have treatments tailored to their specific condition. There are many effective options available, but the key is to work collaboratively with patients so that the right treatment is used as early as possible in the disease course.”