What type of cartilage repair are we attempting to attain?

Abstract

Articular cartilage allows active articulation of diarthrodial joints. This is made possible by a unique set of properties afforded by a very specialized macromolecular organization of an extensive extracellular matrix that is secreted by chondrocytes. Cells within the superficial layer of the cartilage secrete a special lubricant that, together with hyaluronic acid in the synovial fluid, creates an almost frictionless articulation. Articular cartilage is integrated with subchondral bone, the interface of which is partly calcified. Peripherally, cartilage gives way to the synovium, which not only lubricates the joint but also maintains an aseptic environment (cartilage is extremely sensitive to proteolysis induced by contaminant bacteria). With articular cartilage as an interface with subchondral bone, the forces of articulation, consequent upon skeletal movement, are carefully dissipated, thereby protecting the underlying bone from traumatic damage and abnormal excessive loading, which can create pathological changes such as sclerosis. Thus, articular cartilage plays an essential role in joint function. Whenever cartilage is damaged locally or more extensively as a consequence of injury or arthritis, it loses key functional properties, which promotes further pathological changes in surrounding cartilage and neighboring bone. Articulation is altered and opposing articulating surfaces are loaded differently, leading to further pathological changes in surrounding cartilage. During articular cartilage repair, the surgeon should seek to restore these special properties of cartilage while preventing or minimizing the onset of associated pathological changes in the remainder of the joint. Therefore, cartilage repair is not only about restoring functional properties but also about arresting the pathological changes of degenerative arthritis that result from altered loading due to damage to articular cartilage. The purposes of the present report are to better define articular cartilage, to describe its special structure at the macroscopic and molecular levels, to explain the special cellular and molecular processes that create and maintain …