Symptomatic Knee Osteoarthritis Has Increased Greatly

Knee pain associated with osteoarthritis has increased dramatically over the last few decades independent of age and body mass index (BMI), though radiographic osteoarthritis has not increased, a new study finds. The study, carried out by researchers at Boston University Medical School and Brigham and Women’s Hospital, was published online this week in Annals of Internal Medicine.

The researchers set out to test the assumption that the recent increase in knee replacements is the result of an aging and increasingly obese US population. They conducted a cross-sectional study using data from six NHANES (National Health and Nutritional Examination Survey) surveys taken between 1971 and 2004 and from three examination periods in the FOA (Framingham Osteoarthritis) Study between 1983 and 2005. The NHANES participants included were whites and African Americans between the age of 60 and 74, and the FOA participants included were mostly white and all over the age of 70.

The NHANES participants provided information on pain in or around the knees most days. The FOA participants provided information about knee pain and had bilateral weight-bearing anteroposterior knee radiography to gauge the prevalence of radiographic knee osteoarthritis. By comparing findings over time, the researchers determined that the age- and BMI-adjusted prevalence of knee pain increased about 65% in the NHANES data from 1974 to 1999 among non-Hispanic white and Mexican-American men and women and among African-American women. The FOA data found that the age- and BMI-adjusted prevalence of knee pain and symptomatic knee osteoarthritis doubled in women and tripled in men over 20 years. However, there was no similar trend found in the prevalence of radiographic knee osteoarthritis in the FOA participants.

Differences in sampling of FOA study participants over time and birth cohort effects are possible explanations for increased reporting of knee pain. Differences in cohort membership over time may also have played a role. Nonetheless, the results indicate that the prevalence of knee pain has increased a great deal over two decades, independent of age and BMI, but radiographic osteoarthritis has not increased.