Further studies on the anisotropic distribution of collagen in articular cartilage by μMRI.

To further study the anisotropic distribution of the collagen matrix in articular cartilage, microscopic magnetic resonance imaging experiments were carried out on articular cartilages from the central load-bearing area of three canine humeral heads at 13 μm resolution across the depth of tissue. Quantitative T2 images were acquired when the tissue blocks were rotated, relative to B0, along two orthogonal directions, both perpendicular to the normal axis of the articular surface. The T2 relaxation rate (R2) was modeled, by three fibril structural configurations (solid cone, funnel, and fan), to represent the anisotropy of the collagen fibrils in cartilage from the articular surface to the cartilage/bone interface. A set of complex and depth-dependent characteristics of collagen distribution was found in articular cartilage. In particular, there were two anisotropic components in the superficial zone and an asymmetrical component in the radial zone of cartilage. A complex model of the three-dimensional fibril architecture in articular cartilage is proposed, which has a leaf-like or layer-like structure in the radial zone, arises in a radial manner from the subchondral bone, spreads and arches passing the isotropic transitional zone, and exhibits two distinct anisotropic components (vertical and transverse) in the surface portion of the tissue.