CARTILAGE METABOLISM IN THE INJURED AND UNINJURED KNEE OF THE SAME PATIENT

Objective-To examine if unilateral knee injury affects the synovial fl uid concentrations of aggrecan fragments, cartilage oligomeric matrix protein (COMP) fragments, stromelysin-1, and tissue inhibitor of metal loproteinases-1 (TIMP-1) in the contralateral uninjured knee. Methods- Synovial fluids from the injured and uninjured knees were obtained at different times in a group of patients after unilateral knee trauma. S erum samples were obtained on the same occasion. Concentrations of agg recan fragments were determined by precipitation with Alcian Blue; tho se of COMP fragments, stromelysin-1, and TLMP-1 were measured by immun oassay. Concentrations were compared with those in a reference group o f 10 healthy volunteers. Results-Immediately after knee injury, concen trations of aggrecan fragments, COMP fragments, stromelysin-1 and TIMP -1 were increased in the synovial fluid of the injured knee. However, concentrations of aggrecan and COMP fragments, and stromelysin-1 incre ased also in the contralateral uninjured knee immediately after injury , but less than in the injured knee. Subsequently, the concentrations of all markers decreased in the synovial fluid of the injured knee, bu t remained unchanged in the uninjured knee. The concentration of aggre can fragments in the injured knee decreased to less than that in the u ninjured knee in the chronic phase. Serum concentrations of COMP were much smaller than those in synovial fluid. Conclusions-The increased c oncentrations of aggrecan and COMP fragments and stromelysin-1 in the joint fluid of the contralateral, uninjured knee following unilateral knee injury, compared with concentrations in healthy reference knees, suggest changes in joint metabolism in both unilateral knee injury. me chanisms for these changes are unclear. The low serum concentration of COMP makes it less likely that there is any significant 'exchange' of molecular markers between the knees. A further consequence of these f indings is that the contralateral knee cannot be recommended as the on ly control joint in studies of matrix metabolism in patients with unil ateral knee injury.