The half-life of [ 3 H]hyaluronic acid in rabbit knee joints was estimated using two methods:(i) by following the [ 3 H]hyaluronan content of the synovial fluid after intra-articular injection and (ii) by following the 3 H 2 O radioactivity of plasma after intra-articular injection of [ 3 H]hyaluronan.For normal rabbits we obtained a half-life of 15.8 hours (method I) and 17.5 ± 1.0 hours (mean ± SEM, method II), respectively. The second method was used to estimate the kinetics of the hyaluronan elimination from normal, sham-operated, as well as from osteoarthritic rabbit knee joints (Colombo model of osteoarthritis). Four weeks after injury, during the developing phase of osteoarthritis, the half-life of hyaluronan rose significantly to 23.5 ± 2.1 hours and returned to normal levels (17.4 ± 2.7 hours) 12 weeks after the operation (osteoarthritis developed). At the stage of developed osteoarthritis, the clearance rates were considerably higher than in normal rabbits.

The volume of synovial fluid in human knee joints was determined by the dilution method through the intra-articular injection of 35 ml 0.5% hydroxyethyl starch in saline. In 15 control knees the mean synovial volume was 6.7 +/- 2.3 ml (mean +/- SD). In patients with latent gonarthrosis we found a mean intra-articular volume of 13.6 +/- 7.4 ml (n = 21) and in activated gonarthrosis 24.2 +/- 16.3 ml (n = 34). All 3 groups differ significantly. After entire aspiration of the effusion, we found yet 13.4 +/- 4.4 ml (n = 32) synovial fluid in the knee joint. Using the dilution method, we obtained a punctate from each knee joint. The punctates can be used for biochemical investigations. Since the dilution factors of the punctates are known, the concentrations of HWM parameters in the original synovial fluid can be calculated.

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