JRA is the most common chronic inflammatory arthropathy in childhood. It is characterized by arthritis that persists for a minimum of 6 consecutive weeks in one or more joints, commencing before the age of 16 years. The knee joint is the most commonly affected joint. The knee is primarily a hinge joint that is protected anteriorly and posteriorly by muscles with special ligamentous attachments to the capsule. The knee is formed by the femoral and tibial condylar articulations. The tibiofibular articulation , though often considered a part of the knee, is in fact not a portion of the true knee joint. The exact etiology of JRA is unclear. Genetic factors have been suggested, especially association with 2 genetic risk factors, HLA and protein tyrosine phosphatase non-receptor 22 (PTPN22) genes, have been unequivocally confirmed as JRA susceptibility genes in multiple populations. The most well-established genetic factors for JRA are the HLA genes.