Calcified cartilage zone

Figure 11.9 Schematic of articular cartilage structure showing the superficial, middle and deep zones, the tidemark boundary between the noncalcified and calcified cartilage layer, and the subchondral bone that underlies the articular cartilage.

Figure 10.1 Cross-sectional schematic of articular cartilage. The tissue consists of the superficial, middle/transitional, and deep zones with a distinct tidemark of calcified cartilage and the underlying subchondral bone (from top to bottom). Both cellular organization and collagen-fiber orientation are shown with respect to the zonal structure of cartilage.

Oegema Jr., T.R., Carpenter, R.J., Hofmeister, F., Thompson Jr., R.C., 1997. The interaction of the zone of calcified cartilage and subchondral bone in osteoarthritis. Microscopy Research and Technique 37, 324-332. 

In the deep zone, type II collagen is ubiquitous and is oriented perpendicular to the cartilage surface. Although articular cartilage is unmineralized in its surface layers it contains a layer of calcified tissue adjacent to the subchondral bone. 

The overall structure of articular cartilage is analogous to a jelly-filled balloon. The PG-rich middle zone is osmotically pressurized, with fluid restrained from exiting the tissue by the dense coUagen network of the superficial zone and the calcified structure of the deep bone. The interaction between the mechanical loading forces and osmotic forces yields the complex material properties of articular cartilage. 

Allan, K. S., Pilliar, R. M., Wang, J., Grynpas, M. D., and Kandel, R. A. 2007. Formation of biphasic constructs containing cartilage with a calcified zone interface. Tissue Eng. 13 167-177. 

---