Synovial fluid glycosaminoglycan concentration does not correlate with severity of chondropathy or predict progression of osteoarthritis in a canine cruciate deficiency model

Objective. Considerable interest exists today in biochemical or immunochemi cal tests for monitoring the progression of osteoarthritis (OA), It has bee n suggested that measurements made on synovial fluid (SF) will more accurat ely reflect the magnitude of cartilage destruction in an index joint than t hose performed on serum. However, we have shown that the synovitis that occ urs in OA affects the rate of protein clearance from the joint. We tested t he hypothesis that if adjusted for clearance rate, the SF concentration of cartilage proteoglycans (PG) estimates severity of chondropathy and predict s progression of cartilage damage more accurately than if clearance is not taken into account. Methods. Clearance:of radioiodinated serum albumin (RISA), a surrogate for the clearance of PG, was measured in 19 adult dogs at baseline and again 16 weeks and 32 weeks after anterior cruciate ligament transection (ACLT). Se verity of chondropathy was determined arthroscopically after 16 weeks of in stability and at postmortem 32 weeks after ACLT. Results. Adjustment for the RISA clearance rate showed that the SF PG conce ntration markedly under estimated the quantity of PG released from the OA c artilage. Regardless of whether the concentration was adjusted for clearanc e, no correlation existed between the SF PG level and the severity of chond ropathy. Further, the SF concentration of PG 16 weeks after ACLT failed to predict severity of cartilage damage at postmortem. Conclusion. SF concentration of a cartilage derived molecule is unlikely to predict the course of cartilage damage in an OA joint over time or in resp onse to treatment with a potential disease modifying OA drug.