Within the body three subtypes of cartilage can be distinguished: hyaline cartilage, elastic cartilage and fibrocartilage. Hyaline cartilage is the predominant subtype and is mainly located in articular joints and in less extent in the nasal septum and cricoid. Elastic cartilage can be found in the outer ear and in parts of the respiratory tract. The menisci and intervertebral discs are made from the third subtype: fibrocartilage. Hyaline cartilage in joints, further refered to as articular cartilage, is a highly specialized tissue that ensures low-friction movement of articulating bones, whilst transmitting load. The only cell-type present in articular cartilage is the chondrocyte, which only composes less than 5% of the total tissue volume. Water (up to 80% wet weight) is the predominant molecule in cartilage, followed by different collagens (10-20% wet weight) and the group of GAG (GlycosAminoGlycan, 4-7% wet weight) 181. From the latter two groups, collagen type II and aggrecan are the most prominent respectively. A simplified reflection of the cartilage structure and function would be as follows. The collagen molecules form a tightly woven network in which the GAG are contained (Figure I-1 next page). In solution, the GAG is negatively charged and creates an osmotic pressure via attraction of positive counter-ions. This osmotic pressure, together with repulsive forces of the negatively charged GAG, result in a swelling pressure within the matrix that accounts for the excellent capabilities of cartilage to absorb and transmit forces during joint movement and loading. Several smaller molecules also play a crucial role in the extracellular matrix of articular cartilage: decorin, anchorin, collagen type VI, IX and XI. Articular cartilage lacks blood vessels; chondrocytes receive oxygen and nutrients through diffusion from the synovium and the underlying bone. Articular cartilage can be divided in four zones with respect to the architecture 68, 181, 213 (Figure I-2, next page). The superficial zone comprises approximately 10% of the cartilage and is characterized by a high cell density, flattened chondrocytes and thin collagen fibers that are oriented tangential to the articular surface. The middle zone or intermediate zone has randomly orientated collagen fibers and chondrocytes with a more spherical configuration.

Nederlandse Orthopaedische Vereniging (NOV), Dutch Arthritis Association (Reumafonds), Stichting dr. A.A. van Puyvelde Fonds, Ortomed BV, Isotis OrthoBiologics, Stryker Nederland BV, Endo Plus Nederland, Smith & Nephew, DePuy / Johnson&Johnson, Mathys Orthopaedics, Bauerfeind, Somas Chirurgische Techniek, Penders Orthopedische Schoentechniek BV, Van Wijk Orthopedische Schoentechniek BV, Harlan Nederland BV, Jongenengel Orthopedisch Centrum, Stichting Annafonds
J.A.N. Verhaar (Jan)
Erasmus University Rotterdam
hdl.handle.net/1765/39804
Erasmus MC: University Medical Center Rotterdam

Mandl, E. (2004, December). Advances in cartilage tissue engineering : in vitro . Retrieved from http://hdl.handle.net/1765/39804