The value of serum cartilage oligomeric matrix protein (COMP) as a marker of disease progression was investigated in 81 hospital out-patients with clinical knee osteoarthritis (OA). Progressing patients were defined by a decrease of > or = 2 mm in joint space on X-ray or requiring knee surgery during the 5 yr of follow-up. Of the 57 patients for whom full data were available, 20 progressed and 37 did not progress. Serum COMP levels increased during the first year in those who progressed (mean 6.42 micrograms/ml) (S.D. 6.64) compared to those who did not progress [mean 0.07 microgram/ml (S.D. 4.99); P < 0.001]. Changes in COMP during the first year were related to baseline COMP (r = -0.672, P < 0.001) and weight-to-height ratio (r = 0.272, P = 0.47). After allowing for these variables, serum COMP increased during the first year in progressive patients by 5.04 micrograms/ml [95% confidence interval (CI): (2.61, 7.46)] more than in non-progressive patients. Discriminant analysis gave a sensitivity of 70% and specificity of 78% at a cut-off value of 3.17 micrograms/ml. Baseline serum COMP levels did not differ between the groups but were related to late phase scintigraphy scan abnormalities. These observations suggest that the changes in serum COMP may have prognostic significance and are consistent with a model of OA in which early signs of episodic clinical progression can be found in the cartilage as well as in subchondral bone.
Variations in chondrocyte TNF-R expression occur in OA cartilage in vivo. TNFalpha at concentrations produced by OA synovium in vitro, can degrade cartilage matrix. In most OA supernatants sTNF-R concentrations were insufficient to abrogate the effects of TNFalpha. Thus conditions exist in some OA knees for TNFalpha to contribute to focal loss of cartilage.
DXA may provide a safe, rapid and reliable means of assessing knee OA. Cross-sectional age-related subchondral tibial BMD loss is attenuated by knee OA.
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