BIOMECHANICS OF NORMAL HUMAN AND BOVINE MENISCUS

This interdisciplinary investigation is aimed at determining the ANISOTROPIC and INHOMOGENEOUS biomechanical properties of normal bovine and human meniscal tissue. Variations in these properties with orientation relative to the predominant collagen fiber directions, location within the meniscus, and between the medial and lateral menisci will be examined. The motivation for this study is the well documented SIGNIFICANT ROLE THAT THE MENISCI PLAY IN THE FUNCTION OF THE KNEE AND THE LIMITED INFORMATION AVAILABLE REGARDING THE MATERIAL PROPERTIES AND MECHANICAL FUNCTION OF NORMAL MENISCI. Finite element models will be developed using and anisotropic formulation of the biphasic theory to correspond with tissue structure and composition. Specific geometric configurations which accurately represent the experiments will be developed for the determination of tissue properties. Medial and lateral menisci from healthy, skeletally mature bovine and human knee joints will be used. The experimental tests to be employed are: 1) constant strain rate tensile tests, on specimens harvested parallel and perpendicular to the collagen fiber directions, to determine the tensile stress- strain behavior; 2) transient shear relaxation and steady-state dynamic shear tests, on disks oriented in three mutually perpendicular directions, to determine the anisotropic "flow- independent" shear properties; and 3) an "unconfined" compression test, on disk oriented in the same three mutually perpendicular directions, to determine the anisotropic equilibrium compressive properties and solid matrix permeability. A series of finite element models, with increasing geometric and material sophistication, will be constructed--starting with single phase transversely isotropic linearly elastic models and progressing to transversely isotropic linear biphasic theories use for soft hydrated tissue. These models will range from axisymmetric to full three-dimensional representations and will include nonlinearities such as the strain dependent permeability effect and the compressive shear stiffening effect.