Composition of joint fluid in patients undergoing total knee replacement and revision arthroplasty: correlation with flow properties. 
The protein, phospholipid and hyaluronic acid (HA) contents of joint fluid samples were determined in specimens obtained from patients undergoing total knee arthroplasty (TKA) and revision TKA.  It was hypothesized that these components would vary widely among patients undergoing TKA, and that the composition of joint fluid in patients undergoing revision would differ from that in patients undergoing revision.  It was further hypothesized that HA concentration and molecular weight would principally determine the flow properties previously reported.  Biochemical assays were used to assess protein and phospholipid content, and size exclusion chromatography was used to determine HA concentration and molecular weight.  Sixty samples were included in the study.  HA, protein, and phospholipid concentrations all varied widely in patients undergoing index TKA and revision TKA.  HA concentration was lower in patients undergoing revision arthroplasty due to wear-related failure compared to patients undergoing the index procedure (0.9 +/- 0.4 mg/ml versus 1.3 +/- 0.5 mg/ml, mean +/- standard deviation, p = 0.04).  Other components were not different between the groups.  Flow properties at high shear rates were correlated with HA concentration and, to a lesser extent, HA molecular weight, but neither protein nor phospholipid concentration.  The composition of joint fluid is highly variable in the context of arthroplasty.  Much of the variation in flow properties, especially at high shear rate, is explained by large variation in HA concentration and small variation in HA molecular weight.  The variation in composition and lower HA concentration in joints necessitating revision may relate to variation in arthroplasty lubrication leading to highly variable wear rates and clinical outcomes.