Microrheology of human synovial fluid of arthritis patients studied by diffusing wave spectroscopy.

The viscoelastic properties of synovial fluid (SF) are critical to its functions of lubrication and shock-absorption of joints in human body; a change in the viscoelastic properties, even of only a few percents, is often concomitant with arthritis. In this work, the elastic modulus G '(f) and the viscous modulus G ''(f) of SF from patients suffering from three kinds of joint diseases, namely, osteoarthritis (OA), rheumatoid arthritis (RA), and gouty arthritis (GA), were determined as a function of frequency "f " (in the low frequency range from f ∼ 0.1 to 10 Hz) by Diffusing Wave Spectroscopy (DWS) and correlated with the white blood cell (WBC) count. A strong correlation was observed, showing a higher WBC count corresponding to lower elastic and viscous moduli, G ' and G ''; further details depend on inflammatory vs. non-inflammatory, and on the severity of inflammation. Different types of arthritis lead to different degrees of decreasing viscoelasticity. Identical measurements were carried out with a commercial visco-supplementation (or artificial SF) to serve as reference. In general, the reduction in both G ' and G '' was most severe in the case of GA and least severe in the case of OA. Besides, in all cases, the reduction in G ' was more prominent than the reduction in G '', indicating that in general, the deterioration in the elasticity of SF by inflammation is more severe than that in the viscosity. This simple method for quantitative physical characterization of synovial fluid may serve as a useful complementary metric to the conventional biochemical analysis in clinical diagnosis of arthritis.