According to our results, MMP-9 level is higher in patients with RA than in patients with osteoarthritis, both in plasma (19.26 ± 7.54 vs. 14.57 ± 3.11 ng/mL) and synovial fluid (16.17 ± 12.25 vs. 0.75 ± 0.53 ng/mL). Here, MMP9 is linked to osteoarthritis.