MMP9 and osteoarthritis: MMPs include collagenases (MMP-1, MMP-8, and MMP-13), stromelysins (MMP-3, MMP-7, MMP-10, and MMP-11), and gelatinases (MMP-2 and MMP-9), among which the gelatinase group rapidly increases its activity in an animal model of MIA-induced osteoarthritis, promoting matrix degradation of cartilage and subchondral bone [18,19,20].