[Time-dependent flow behavior and fibrinogen content of synovial fluid]

Normal bovine synovial fluid and synovial effusions in human non-inflammatory joint diseases do not show any decrease of viscosity for a long period of time during imposed shear loading, as is required for thixotropy. This observation is based on two different methods of measurement; the "hysteresis loop" method and the recording of the shear stress-time curve. Inflammatory synovial fluids--particularly from patients with rheumatoid arthritis and a high concentration of fibrinogen--form a visible gel after 6 to 20 hours of rest. Those gels show a hysteresis loop typical for thixotropy and a decrease of viscosity with the duration of shear loading. Due to the shearing in the rheometer precipitation occurs and fibrin clots appear. The appearance of fibrin clots induced by mechanical shear loading not known until now, can be discussed with regard to its possible participation in the symptom of morning stiffness, in the formation of rice bodies and in the destruction of joint cartilage in rheumatoid arthritis.