MMP13 and synovitis: Synovitis ointment reduces the expression of SDF-1, CXCR4, MMP-9, and MMP-13 in rats with KOA, decreases the increase of knee joint diameter, alleviates KOA injury, inhibits the expression of PLOD2, COL1A1, TIMP1, and TGF-β mRNA to prevent osteoblast fibrosis, and finally promotes knee joint recovery.