Body fluid markers of cartilage changes in osteoarthritis.

Various markers of the metabolism of articular cartilage have been identified in synovial fluid, blood, and urine of patients with osteoarthritis (OA). The joint fluid level of a cartilage-derived molecule, or its fragment, can be used as a marker of the synthesis or catabolism of that molecule in the articular surfaces within that joint. In blood and urine, on the other hand, the level of a marker is useful in assessing systemic changes affecting the metabolism of a molecule in all the cartilages in the body. Quantification of specific markers in body fluids already has proved useful in identifying increased catabolic as well as anabolic activities in articular cartilage during preradiologic as well as later stages of OA. The markers also can be sued for monitoring the effect of drugs on cartilage matrix molecules and in differentiating among different subtypes of osteoarthritis. Markers should prove most useful in prospective studies aimed at identifying early changes in cartilage metabolism in humans at high risk for developing OA.