MMP3 and synovitis: Studies have shown that MMP-3 is not directly involved in the progression of synovitis, but the products of decomposing cartilage matrix, such as cartilage oligomeric matrix protein and damage-associated molecule patterns, can recruit inflammatory cells, leading to synovitis (Foell et al., 2007; Huang et al., 2015; Haraden et al., 2019).