Fig. 1.

Schematic summary of arthritis pathogenesis. Pathological changes, such as swelling, synovial membrane outgrowth and inflammation (synovitis), are observed in both OA- and RA-affected joints. Although the inflammatory state is an important factor in the development of OA, it is not as critical as in RA, which is a typical inflammatory disease. In the synovial fluid, several inflammatory factors, such as cytokines, chemokines, macrophages, neutrophils, fibroblasts, chondrocytes and osteoblasts, can be found. Gradual cartilage degeneration, which is characteristic of OA progression, causes bone exposure and pain, while released cartilage fragments potentiate synovitis within the joint capsule