Radial tie fibers influence the tensile properties of the bovine medial meniscus

Abstract

Although collagen fibers are arranged predominantly in the circumferential direction in the knee meniscus, there is evidence for radially oriented fibers within human menisci. A bovine medial meniscus model was used to study the hypothesis that radial fibers alter the radial tensile properties of the meniscus. The architecture of the collagen network 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 microns thick. Polarized light microscopy showed that the distribution of radial tie fibers varied greatly among the anterior, central, and posterior regions. These radial tie fibers were larger and more frequent in the posterior region. Radial fibers persisted over many adjacent sections with similar architecture, which led to our hypothesis that they may be arranged in continuous sheets in which the morphology varies by region. Radially oriented specimens for tensile testing were grouped according to the number of radial tie fibers (full, partial, and no fiber) and region (anterior, central, and posterior). Uniaxial tensile testing was performed on a testing machine at a strain rate of 0.00017 sec-1 until failure. The tensile modulus, ultimate tensile stress, and ultimate tensile strain were determined. The presence of radial tie fibers in the specimen had a significant effect on the tensile modulus and ultimate tensile stress. Specimens containing full radial tie fibers were stiffest and failed at the lowest strains; in specimens from the posterior region, the tensile modulus was 392%, the ultimate tensile stress was 314%, and the ultimate tensile strain was 68% that of the specimens with no radial fibers. In no-fiber specimens, the tensile modulus in the posterior region was 225% of the modulus in the anterior region, and 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 by these radial fibrous sheets may be well suited to the manner in which the bovine medial meniscus functions in load-bearing.

Compressive moduli of the human medial meniscus in the axial and radial directions at equilibrium and at a physiological strain rate

“…The modulus values in their study were in the range of 15-60 MPa, found from studies which tested bovine and human menisci in tension. 8,21,22 Because the compressive moduli in our study at 12% strain are several orders of magnitudes smaller, they may provide a more accurate contact pressure distribution. The moduli values used in a knee joint model should be based on whether standing or walking is of interest, because these values differ greatly (Tables 1 and 2).…”

“…Our compressive moduli are orders of magnitude smaller than the tensile moduli in the same direction. 8,21,22 This large disparity is likely important in tibiofemoral joint models.…”

Thickness of the Meniscal Lamellar Layer: Correlation with Indentation Stiffness and Comparison of Normal and Abnormally Thick Layers by Using Multiparametric Ultrashort Echo Time MR Imaging

“…MR hardware.-A 3-T MR imager (Signa HDx; GE Healthcare, Milwaukee, Electron microscopy imaging studies (14) revealed three distinct layers in meniscal cross section (Fig 1): a superficial network that covers the femoral and tibial surfaces by a meshwork of very thin fibrils (30 nm); a lamellar layer beneath the superficial network, represented by a layer of lamellae of collagen fibrils (150-200 mm); and a central main portion, composed of predominantly circular-oriented bundles of collagen fibrils with occasional radial-tie fibers (15). By using UTE MR images, the anatomic structure of the menisci, including the lamellar layers and radial-tie fibers, were made visible (4).…”

Regional Effects of Enzymatic Digestion on Knee Meniscus Cell Yield and Phenotype for Tissue Engineering

“…The inner portion of the meniscus is similar to hyaline cartilage in that it contains the majority of sulfated GAGs and collagen type II (Col 2), whereas the middle and outer meniscus regions contain a higher proportion of collagen type I (Col 1). [29][30][31][32][33] The morphology of meniscus cells also becomes progressively more fibroblast-like peripherally in the meniscus, with the inner region cells more rounded and chondrocyte like and the outer cells containing more cellular processes. 34 In addition to morphology, regional cell phenotypic differences are observed; cells in the outer meniscus show high gene expression for Col 1, while cells from the inner region display high gene expression for Col 2 and aggrecan (AGC).…”