RADIAL TIE FIBERS INFLUENCE THE TENSILE PROPERTIES OF THE BOVINE MEDIAL MENISCUS

Although collagen fibers are arranged predominantly in the circumferen tial direction in the knee meniscus, there is evidence for radially or iented fibers within human menisci. A bovine medial meniscus model was used to study the hypothesis that radial fibers alter the radial tens ile properties of the meniscus. The architecture of the collagen netwo rk and tensile properties of the bovine medial meniscus were examined; attention was given to large ''radial tie fibers'' and their regional variation. Menisci were sectioned serially into slices 400 mu m thick . Polarized light microscopy showed that the distribution of radial ti e fibers varied greatly among the anterior, central, and posterior reg ions. These radial tie fibers were larger and more frequent in the pos terior region. Radial fibers persisted over many adjacent sections wit h similar architecture, which led to our hypothesis that they may be a rranged in continuous sheets in which the morphology varies by region. Radially oriented specimens for tensile testing were grouped accordin g to the number of radial tie fibers (full, partial, and no fiber) and region (anterior, central, and posterior). Uniaxial tensile testing w as performed on a testing machine at a strain rate of 0.00017 sec(-1) until failure. The tensile modulus, ultimate tensile stress, and ultim ate tensile strain determined. The presence of radial tie fibers in th e specimen had a significant effect on the tensile modulus and ultimat e tensile stress. Specimens containing full radial tie fibers were sti ffest and failed at the lowest strains; in specimens from the posterio r region, the tensile modulus was 392%, the ultimate tensile stress wa s 314%, and the ultimate tensile strain was 68% that of the specimens with no radial fibers. In no-fiber specimens, the tensile modulus in t he posterior region was 225% of the modulus in the anterior region, an d the ultimate tensile strain in the posterior region was 68% that of the strain in the anterior region. The abundance of radial tie fibers in the posterior region seems to contribute to the increased stiffness of this region. The preferential stiffening of the posterior region b y these radial fibrous sheets may be well suited to the manner in whic h the bovine medial meniscus functions in load-bearing.