Cartilage Biology: Essentials and Methods

Abstract

Articular cartilage is the clinically most relevant hyaline cartilage since frequently damaged by trauma or abuse but without any intrinsic potential to regenerate. It covers the ends of the bones and allows frictionless movement due to its stiff and elastic properties. The biomechanics and consecutive function of articular cartilage are determined by its composition and morphological organisation. Knowledge about the cartilage biology is essential to understand its function, potential, durability and vulnerability. This chapter explains the histological organisation and ultrastructural details of this tissue, which is dominated by extracellular matrix with a special arrangement of collagen and a high amount of proteoglycans that are produced by the chondrocytes embedded in between. The chondrocytes, even if capable to metabolise and regenerate the matrix, are not able to migrate through their dense environment. In case of tissue damage, this means that they may not approach the defect to fill gaps and regenerate degraded or lost tissue. Chondrocytes are specialised cells that persist under the hypoxic conditions of the dense matrix. Their special microenvironment and a sensory organ, the cilium, allow to detect changes in the mechanical conditions on which they react by matrix synthesis or, in contrary, by degradation. These initial changes and cartilage remodelling remain though unrecognised since the tissue is not innervated. Consequently, degradation is proceeding until reaction of the surrounding tissues in the joint cavity and finally causes pain in an advanced stage of degradation. Regeneration, which is possible in young patients, requires the development of the complex hyaline cartilage tissue which is described in this chapter.