OA prevalence (all cases). The National Arthritis Data Workgroup (NADW) used the best available data to estimate that in 2005, 27 million U.S. adults ages 18 years and older had one or more type of clinical OA.13 Most of what is known about the prevalence of symptomatic OA is from the Framingham OA Study (a study of knee and hand OA among adults in a suburb of Boston) and the Johnston County Osteoarthritis (JoCo OA) Project (a study of knee and hip OA among blacks and whites ages 45 years and older in Johnston County, North Carolina).12, 13 We did not identify any population-based data on OA of the spine.