Basic Science and Articular Cartilage Healing
Articular cartilage has no blood supply and no nerve supply. Chondrocytes (articular cartilage cells) obtain their nutrition from the synovial fluid while the underlying bone provides nutrition to the deeper layers. Chondrocytes function to produce the extracellular matrix and work hard to produce proteoglycans. Collagen fibres turn over less rapidly than the proteoglycans and this process means that articular cartilage is capable of responding to mechanical changes.
Repair, therefore, can be stimulated by mechanical input such as load bearing and this may result in increased matrix and collagen production.
However, sudden overload or damage can cause breakdown of the articular cartilage with death of the cells and loss of the extracellular matrix. Processes that affect the bone underlying the articular cartilage may lead to stiffness of the bone and thereby alteration of the shock absorbing property and possibly result in overload on the articular surface and degeneration.
When articular cartilage tries to heal it is not possible for the normal healing process from blood vessels to occur and in addition chondrocytes are restricted from migration as they are held within the cartilage. Repair processes can however occur when the cartilage damage is deep enough to affect the subchondral bone as this allows for invasion of cells.