Studying the Natural History of the Knee Joint.

By the time the orthopaedic surgeon sees a patient with symptomatic knee osteoarthritis, the disease has already progressed to an advanced stage. As a result, studying the full natural history of the knee is especially difficult. A few large longitudinal cohorts, the Osteoarthritis Initiative and Multicenter Osteoarthritis Study in particular, provide the bulk of the data for most extant studies. In this review, we report on the current state of knowledge regarding the study of the natural history of the knee, including the difficulties of natural history research, the tools used to assess knee osteoarthritis, the major longitudinal studies in knee osteoarthritis, and the ability of early interventions to modify natural history. In addition, we will preview what is possible using artificial intelligence and newer large longitudinal cohorts.