Articular cartilage lies at the end of bones at the joint. It is very smooth (its coefficient of friction is less than one-third of ice on ice) highly compressible and resilient.
Articular cartilage derives its powers from its very organized and efficiently constructed microanatomy. At the base, horizontal fibers are firmly adherent to the subchondral bone. Above that layer, large, negatively charged macromolecules attract and bind water. This hydration gives the cartilage springiness needed for shock absorbency. Finally, the top layer of the cartilage has another set of tangentially oriented collagen fibers. These serve as a 'skin' to protect the cartilage from sheering forces.
Breakdown of articular cartilage leads to osteoarthritis