INCREASED CONCENTRATIONS OF BONE SIALOPROTEIN IN JOINT FLUID AFTER KNEE INJURY

Objective-To detect evidence for localised changes in bone matrix meta bolism after joint trauma and in post-traumatic osteoarthritis by quan tification of bone sialoprotein in joint fluid and serum after knee in jury in a cross sectional study. Methods-Samples of knee joint fluid a nd serum were obtained from volunteers with normal knees (n = 19), pat ients with rupture of the anterior cruciate ligament isolated or combi ned with tear of a meniscus (n = 114), and patients with isolated meni scus lesions (n = 80). Concentrations of bone sialoprotein were determ ined by ELISA. Concentrations of other markers of joint tissue metabol ism in these samples were determined in previous investigations. Resul ts-The median concentration of bone sialoprotein in joint fluid from h ealthy volunteers was 122 ng ml(-1) (range 41 to 183). Concentrations of bone sialoprotein were increased in both injury compared with the r eference (median for cruciate ligament injury 146 ng ml(-1), range 72 to 339; median for meniscus injury 166 ng ml(-1), range 75 to 376). Af ter injury, bone sialoprotein increased quickly and remained increased for six months. Bone sialoprotein in joint fluid was increased only i n samples from joints with normal or nearly normal (fibrillated) carti lage, and was within reference range in joints with radiographic signs of osteoarthritis. Bone sialoprotein concentrations in joints with cr uciate ligament injury were positively correlated with levels of aggre can and cartilage oligomeric matrix protein fragments, and with levels of stromelysin-l and tissue inhibitor of metalloproteinase-l. The rat ios between the concentrations of bone sialoprotein in joint fluid and serum were >1 in the majority of the cruciate ligament injury cases. Conclusions-The release of significant amounts of bone sialoprotein in to joint fluid in connection with acute joint trauma may be associated with injury to, and active remodelling of, the cartilage bone interfa ce and subchondral bone. The findings are consistent with dramatic shi fts in cartilage, bone, and synovial metabolism following joint injury . Bone sialoprotein concentrations in synovial fluid may be a useful m arker of subchondral injury following joint injury.