Affiliations: [a] Division of Mechanics, Chalmers University of Technology, S-41296 Gothenburg, Sweden | [b] Department of Rheumatology, Sahlgren Hospital, 413 45 Gothenburg, Sweden | [c] Department of Orthopaedic, Sahlgren Huspital, 413 45 Gothenburg, Sweden
Note: [] Accepted by: Editor T.C. Laurent
Abstract: For the first time it is clearly exhibited that synovial fluid (SF) is thixotropic. Although rio hysteresis loops were observed for SF, not even at high shear rates, thixotropy may be exhibited by measuring the rate of recovery after extensive shearing. The rebuilding of the structure in a small-amplitude oscillatory state following the high-shear-rate state reveals the thixotropic behaviour. Five different viscoelastic parameters for various synovial fluids (SF) were obtained using oscillatory rheometry. It was also shown that for SF in the low frequency range, corresponding to a knee joint almost at rest, the shear loss modulus G″ is greater than the shear storage modulus G′, since the system is allowed to dissipate energy at rest. However, with movement, G′ increases and eventually becomes greater than G″ at a characteristic frequency above which the system has insufficient time to dissipate energy and hence responds as an elastic body. This functional behaviour, characteristic for normal SF, broke down in the SF of rheumatoid arthritis. It was also absent in the SF of knee joints with meniscus lesions and ligament defects.
Keywords: synovial fluid, thixotropy, rheumatic disease, zero shear viscosity, relaxation time, phase lag, dynamic moduli, meniscus lesion, linear viscoelastic behaviour
DOI: 10.3233/BIR-1990-27504
Journal: Biorheology, vol. 27, no. 5, pp. 659-674, 1990
