COMP and synovitis: In an animal experiment on osteoarthritis of the guinea pig knee, Kanwat et al. injected allogeneic PRP into the knee cavity of the affected limb and showed that synovitis was significantly improved and knee synovial fluid COMP levels were significantly reduced in a short-term analysis, but the beneficial effects of PRP observed in the short-term were not reproduced in long-term observations [31].