Identification of important interactions between subchondral bone ...
Identification of important interactions between subchondral bone ...
Identification of important interactions between subchondral bone ...
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CHAPTER 2: Introduction<br />
Cartilage is divided into different zones that have different chondrocyte phenotypes,<br />
compositions, structures, and biomechanical properties (fig. 7). From the articular cartilage<br />
surface and down to the <strong>subchondral</strong> <strong>bone</strong>, we find the superficial zone, the middle zone, the<br />
deep zone and the calcified cartilage zone (fig. 7A). Since the superficial zone is exposed to<br />
compression, tensile forces and diffusion, it has flattened chondrocytes and is rich in collagen<br />
fibres that are parallel arranged to the surface (fig. 7B). In the middle zone, chondrocytes have a<br />
spherical shape and are randomly distributed. The collagen fibres are arranged in an angulated<br />
manner at which the compression load is better dispersed. The deep zone is responsible for<br />
providing the greatest resistance to compressive forces. The collagen fibres are arranged in a<br />
radial disposition, with the highest proteoglycan content, and the lowest water concentration. The<br />
chondrocytes are still spherical, but are typically arranged in columnar orientation parallel to the<br />
collagen fibres. The tide mark distinguishes the deep zone from the calcified cartilage zone. The<br />
calcified layer plays an integral role in securing the cartilage to <strong>bone</strong> by anchoring the collagen<br />
fibrils <strong>of</strong> the deep zone to the <strong>subchondral</strong> <strong>bone</strong>. In the calcified zone, the cell population is<br />
scarce and chondrocytes are hypertrophic 57,58 .<br />
Fig. 7. Schematic illustration <strong>of</strong> the zones observed within<br />
articular cartilage. A) 3D view <strong>of</strong> articular cartilage divided in<br />
different zones. B) The arrangements <strong>of</strong> collagens in the different<br />
zones are illustrated in the boxes next to the cartilage zones. Adapted<br />
with modifications from Sah et al. 59 .<br />
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