Fig. 1

The inflammatory microenvironment of articular cartilage induced in OA. Chronic inflammation is an important pathological feature of OA and is a major factor in the destruction of cartilage; it also leads to persistent inflammation of the chondrocytes. Phagocytic clearance of chondrocyte degradation products, deceased chondrocytes, and chondrocyte-derived exosomes by synovial macrophages exacerbates the synovial inflammatory response. Inflammatory synovial cells generate pro-inflammatory factors, further intensifying chondrocyte degradation and establishing a vicious spiral. The activation of immune cells within the synovial membrane, such as B cells, T cells, and macrophages, increase the inflammatory level. Additionally, both synovium and cartilage produce anti-inflammatory cytokines to help modulate the inflammatory milieu