The CHECK study, based in the Netherlands, aims to assess the symptoms of early osteoarthritis and identify the underlying mechanisms and progression of the condition. Participants aged 45 to 65 years were recruited from hospitals across the Netherlands, including those in Amsterdam, Rotterdam, and Utrecht. The study includes individuals who visited the hospital for knee and hip pain, divided into an annual visiting group (with more serious symptoms) and a variable visiting group (with milder symptoms). The annual visiting group is followed up each year, while the variable visiting group is assessed at years 0, 2, 5, 8, and 10.