Anisotropic viscoelastic shear properties of bovine meniscus.

The objectives of this study were to determine the viscoelastic shear properties of bovine menisci and to examine those variations with respect to the structural organization of the tissue. Disc shaped meniscal specimens were subjected to: (1) oscillatory shear deformation over a physiological range of frequencies (1-100 rads per second), and (2) shear deformation in the range of infinitesimal strains (0.005-0.05 rad). The dynamic shear modulus and the transient shear stress relaxation function were determined from the experiments. The dynamic shear modulus was measured at 3 levels of compressive strain (7%, 10%, 13%). Directional variations in shear properties were examined by testing axially, radially, and circumferentially oriented specimens. The experiment showed that meniscal tissue exhibits intrinsic viscoelastic behavior in shear that depends on frequency, shear strain, and compressive strain. Shear anisotropy is evident and is dependent upon compression. At low compressive strains (< or = 10%), the circumferentially oriented specimens were found to be stiffer in shear than the axially and radially oriented specimens. At high compressive strains (> 10%), no statistically significant difference was found between the circumferentially and axially oriented specimens. These results suggest that the anisotropic shear properties of the meniscus are related to the collagen fiber orientation within the meniscus.