IL6 and synovitis: Synovitis is characterized by the production of inflammatory cytokines, such as interleukin (IL)-1, IL-6, tumor necrosis factor (TNF)-α, and vascular endothelial growth factor (VEGF), infiltration of mononuclear cells, thickening of the synovial lining layer, and fibrosis that appears from the early stage of OA, and is associated with symptoms and structural progression including cartilage damage in OA [34].