Earlier Onset Knee Osteoarthritis Impacts Healthcare System

Chicago—New data highlight the increasing number of people in the United States newly diagnosed with knee osteoarthritis (OA), particularly younger people, and the additional burden it is estimated this will place on the US healthcare system due to the increased need for total knee replacements, among other factors. A study presented in an oral abstract session and at a news conference at the ACR meeting showed that physician-diagnosed symptomatic knee OA occurred on average 16 years earlier in life in 2010 compared with the early 1990s. Based on this dramatic shift and current trend toward younger age at diagnosis, the study estimated that nearly 6.5 million people from the United States between 35 and 84 years of age will be diagnosed with knee OA within the next 10 years. Of these, more than half are expected to occur in persons 45 to 64 years of age. “Policymakers and planners can use our estimates to prepare for the expected future burden on the US healthcare system resulting from the earlier age of diagnosis of symptomatic knee osteoarthritis,” said Elena Losina, PhD, associate professor of orthopedic surgery at Harvard Medical School and codirector of the Orthopedics and Arthritis Center for Outcomes Research at Brigham and Women’s Hospital in Boston, who presented the results at the meeting. In the study, investigators estimated and compared the age-stratified 10-year incidence of symptomatic physician-diagnosed knee OA in the 1990s and 2010 by using a validated computer simulation model of the natural history of knee OA called the Osteoarthritis Policy Model, which Dr. Losina helped develop. The researchers used the model to simulate the onset and progression of knee OA in persons with demographic characteristics similar to the US-based population from 25 years of age until death. Data were derived from the published literature for the 1990s symptomatic knee OA incidence and from the National Health Interview Survey 2007-2008 for the 2010 incidence. To project the number of incident cases of knee OA in the US population over a 10-year period, the researchers coupled model output and the Centers for Disease Control and Prevention estimates from each time period. They then compared the ages of onset of knee OA and 10-year cumulative incidence of knee OA for the 2 time periods. The study found that the mean age of physician-diagnosed knee OA fell from 72 years in the 1990s to 56 years in 2010. In 2010, persons between 35 and 84 years of age were expected to incur >6 million incident cases of symptomatic knee OA over the next 10 years, with the majority (59%) of these persons aged 45 to 64 years. The trend toward earlier diagnosis of symptomatic knee OA was highlighted by estimates that showed a greater 10-year cumulative incidence of knee OA expected in persons 45 to 54 years of age at baseline in 2010 compared with those in the same age group at baseline in the early 1990s. The study found that for persons 45 to 54 years of age in the early 1990s, an estimated 412,214 incident cases of knee OA were expected over the next 10 years compared with 2,108,881 incident cases expected over the next 10 years for the same-aged persons in 2010. This represents a 10-year cumulative incidence of 1.5% versus 4.8%, respectively. Compared with the younger cohort, the projected number of 10-year incident cases among those 65 to 74 years of age at baseline decreased slightly between the 1990s and 2010s (from 1,169,615 to 882,997 cases). According to Dr. Losina, the trend toward younger age at diagnosis of knee OA may reflect the increased prevalence in recent years of obesity and knee injuries. She also said that patients’ demands for earlier and more aggressive treatment may contribute to earlier presentation for care. “Our findings present strong evidence in support of directing resources toward modifying risk factors for knee OA and increasing awareness of the disease in younger US adults,” she said.