Die Oberfläche des Gelenkknorpels: Struktur und Funktion
Articular cartilage surface structure and function
Nixon A J
DOI: 10.21836/PEM19930202
Jahr: 1993
Volume: 9
Ausgabe: 2
Seiten: 95-100
Hyaline articular consists of condrocyts and matrix composed of collagen fibres and a well hydrated ground substance made up of proteoglycans and glycoproteins. Normal, mature anicular cartilage is avascular, aneural and alymphatic, having sparsely scattered chondrocytes in an abundant extracellular matrix. The chondrocytes synthesise a matrix that is for cartilage function such as compressive stiffness, smooth gliding action, durability and load distribution. Collagens give cartilage tensile properties, whereas proteoglycans give compressive stiffness. Proteoglycans are the major macromolecule of the cartilage ground substance occupying the spaces between the collagen fibrils. They take several forms and consist of monomers formed by a protein core and glycosaminoglycan (GAG) side chains. Most (85 %) form large aggregates by non-covalent attachements to a hyaluronic acid filament. Attachement of the proteoglycan core protein to the hyaluronic molecule is stabilised by link protein. A unique interaction exists between chondrocytes and the surrounding matrix. This made be facilitated by a cilium from each chondrocyte, which extends into the matrix and acts as a "probe" sensing changes in the matrix composition. This information is relayed to cell organelles responsible for matrix synthesis. There is a bidirectional nutrition of the articular cartilage. The deeper layers are nourished by epiphyseal vessels. The surface layers of cartilage, however, rely on the synovial fluid and matrix water exchange for chondrocyte metabolism and waste exchange. Under physiological loads, cartilage can be compressed to 40 % of its original height. The expression of water and its subsequent return provide a "pumping action" for solutes to, and wastes from, the chondrocytes in the depths of the cartilage. The depth to which this diffusive nutritional gradient can extend is limited. Abnormalities in enchondral ossification in the depths of the articular-epiphyseal complex cartilage result in excessively thickened canilage that outgrows the limits of the diffusion gradient. The thick cartilage then becomes increasingly susceptible to mechanical injury and can cleft from subchondral bone, producing an OCD flap. There is a gradual decline in chondrocytes density with funher ageing. Cell population changes result in marked differences in the repair capacity following cartilage injury in young and older animals.