Osteoarthritic synovial fluid rheology and correlations with protein concentration.

BACKGROUND Osteoarthritis is a common, localized joint disease that causes pain, stiffness and reduced mobility. Osteoarthritis is particularly common in the knees. The effects of osteoarthritis on the rheology of synovial fluid in the knees are not fully understood and consequently require further study. OBJECTIVE The purpose of this study is to investigate the effects of protein content on synovial fluid shear rheology. A secondary study outcome will include study of the temperature dependence of synovial fluid behaviour. METHODS 38 osteoarthritic synovial fluid samples were studied under shear flow. Shear properties were correlated with protein concentration. Viscosupplement was used as a comparison and to verify measurement reliability. The effects of temperature were investigated at 20, 29 and 37°C. RESULTS Shear rheological properties were found to vary widely between samples, however all samples demonstrated clear non-Newtonian shear thinning behaviour. In general viscoelastic properties were lower in osteoarthritic samples than previously studied healthy synovial fluid. A moderate correlation was observed between synovial fluid dynamic moduli at a frequency of 2.5 Hz and protein concentration. Temperature was found to affect the rheology of osteoarthritic synovial fluid and was fitted with the Arrhenius model. CONCLUSIONS Increased protein concentration has been correlated with decreased shear rheological parameters. Temperature dependence of synovial fluid was also demonstrated and modelled for use in Part 2 of this article.