THE USE OF THE PSEUDOPLASTIC PROPERTIES OF PATHOLOGICAL SYNOVIAL-FLUID AS AN AID TO DIAGNOSIS

The rheological properties of synovial fluids from osteoarthritic and rheumatoid arthritic knee joints were determined, using simple shear i n a Wells and Brookefield cone and plate viscometer. The now curves ob tained were then treated mathematically using the Ostwald Power Law eq uation (which has been used by some researchers in the past) to simpli fy the data for the clinician. Two mathematical constants n (Newtonian index) and k (Viscosity index) were determined. There were shown to b e significant differences between the two disease types, with n values significantly lower and k values significantly higher for osteoarthri tic fluids compared with rheumatoid arthritic samples. For fresh synov ial fluid samples there was a 93.3% successful disease classification which dropped to 86.7% for frozen fluids. To test the wider applicabil ity of this test, it was applied to three other studies, producing a s uccessful disease classification of 81.6% for the combined results. In addition the Pseudoplastic Ratio method was performed to determine th e degree of pseudoplasticity of both osteoarthritic and rheumatoid art hritic fluid samples. Results revealed that osteoarthritic fluids exhi bited a significantly greater degree of pseudoplasticity compared with rheumatoid arthritic fluids. However this difference in pseudoplastic behaviour was only evident on the shear rate ramp up (85.0% correct d isease classification) and not on the shear rate ramp down. Thus it is proposed that the Ostwald Power Law equation, possibly in conjunction with the ratio method, could form the basis of a diagnostic test to a id in clinical decision making, which is easily carried out, requires 1.0 ml sample volume and requires a standard procedure applied to each fluid tested.