The orientation of collagen fibrils in normal articular cartilage, as expounded in the classic arcade model of Benninghoff. Collagen fibers arise from the subchondral bone where they are radially oriented, curve over to lie parallel to the cartilage surface in the superficial tangential layer, and then descend back to the underlying bone. The tangential layer is generally less than thick, while the majority of the full thickness of the cartilage ( or so) is occupied by the transitional and radial zones.
A contemporary view of collagen organization in cartilage based on cryofracture SEM imaging of cartilage in three mutually orthogonal planes, one of which is determined by the local split-line direction (reproduced from Jeffrey et al.). The collagen fibers arise from the bone and curve over to form a lamellar network in the tangential zone but do not descend back to the bone.
PS-OCT retardance images of equine cartilage as a function of the incident beam polar angle. The lack of banding in the upper image (corresponding to a vertical incident beam) suggests that the collagen fibers are oriented close to the vertical also, as confirmed by the appearance of stronger banding (i.e., birefringence) for angles of incidence away from the vertical (middle and lower curves). Reproduced from Ugryumova et al. 2006 with permission.
Fiber polar angles at various points around the sagittal ridge of the equine third metacarpophalangeal joint, as determined by applying Eq. (2) to birefringence values extacted from image sets similar to Fig. 3. Reproduced from Ugryumova et al. 2006 with permission.
Schematic representation of 3D structure of cartilage fibers in the equine third metacarpophalangeal joint as derived from multiangled PS-OCT measurements. Reproduced from Ugryumova et al. 2009 with permission.
Illustrating the morphological appearance of normal (upper row), diseased (low row), and intermediate (middle row) of SHG (left column) and TPEF (right column) images of equine cartilage. (Reproduced from Mansfield et al. 2008 with permission).
Total SHG intensity vs polarization angle for normal (upper row), diseased (lower row), and intermediate (middle row) samples of equine cartilage (Reproduced from Mansfield et al. 2008).
Schematic showing the relationship between a collagen fibril (oriented along the -axis), the applied electric field , and the FA of the birefringent material lying between the fibril and the incident laser beam. The incident electric field vector subtends an angle to the fibrillar long axis. The birefringence SA subtends an angle (for completeness, not necessarily equal to zero) to the -axis.
Simulated versions of Fig. 7 using Eqs. (6) and (7) with parameters , , , and equivalent to a quarter-wave plate at depth (upper graph) and (lower graph).
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