[Viscoelastic properties of normal human synovia and their relation to biomechanics]

The viscoelastic parameters of synovial fluid (SF) collected from donors with healthy joints were investigated in a shear rate range between D = 10(-3) to 10(+3) s-1. The rheological parameters obtained from these SF yielded a common Master-curve, which can be accepted as characteristic for healthy human FS: it shows high zero shear viscosity (6-60 Pa X s) and pronounced shear thinning with increasing shear rates. The shear module G, calculated from the first normal stress difference, shows a constant range with values between 1 and 5 Pa. The largest average relaxation times are observed in the range of 2 to 5 s, and they decrease linearly with increasing shear rate to values of 0.01 to 0.05 s. The above viscoelastic properties appear to be necessary for the formation of a fluid film to guarantee optimal joint lubrication and to protect the cartilage from mechanical damage.