Osteoarthritis (OA), one of the most common rheumatic disorders, is characterized by cartilage breakdown and by synovial inflammation that is directly linked to clinical symptoms such as joint swelling, synovitis and inflammatory pain. The gold-standard method for detecting synovitis is histological analysis of samples obtained by biopsy, but the noninvasive imaging techniques MRI and ultrasonography might also perform well. The inflammation of the synovial membrane that occurs in both the early and late phases of OA is associated with alterations in the adjacent cartilage that are similar to those seen in rheumatoid arthritis. Catabolic and proinflammatory mediators such as cytokines, nitric oxide, prostaglandin E2 and neuropeptides are produced by the inflamed synovium and alter the balance of cartilage matrix degradation and repair, leading to excess production of the proteolytic enzymes responsible for cartilage breakdown. Cartilage alteration in turn amplifies synovial inflammation, creating a vicious circle. As synovitis is associated with clinical symptoms and also reflects joint degradation in OA, synovium-targeted therapy could help alleviate the symptoms of the disease and perhaps also prevent structural progression.
Substantial synovial inflammation can occur in early-stage osteoarthritis (OA), end-stage OA, or both
Synovitis triggers several symptoms and clinical signs of OA
OA synovitis can be assessed by MRI, ultrasonography and arthroscopy; however, the gold-standard method for detecting OA synovitis is histological analysis of biopsy-obtained samples
Synovial inflammation can predict cartilage breakdown in OA
OA synovitis perpetuates the processes of cartilage degradation
The OA synovium releases several soluble mediators that could hold promise as biomarkers or therapeutic targets
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The authors declare no competing financial interests.
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Sellam, J., Berenbaum, F. The role of synovitis in pathophysiology and clinical symptoms of osteoarthritis. Nat Rev Rheumatol 6, 625–635 (2010). https://doi.org/10.1038/nrrheum.2010.159
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