Cartilage as the cricoid cartilage and carina. Cartilage is composed of specialized cells called chondrocytes that produce a large amount of collagenous extracellular matrix, abundant ground substance that is rich in proteoglycan and elastin fibers. Cartilage is classified in three types, "elastic cartilage", "hyaline cartilage" and "fibrocartilage", which differ in relative amounts of collagen and proteoglycan. Cartilage does not contain blood vessels (it is avascular) or nerves (it is aneural). Nutrition is supplied to the chondrocytes by diffusion. The compression of the articular cartilage or flexion of the elastic cartilage generates fluid flow, which assists diffusion of nutrients to the chondrocytes.
Articular cartilage repair to maintain a higher activity level that traditional joint replacements would not allow. Advances in tissue preservation and surgical technique are quickly growing this surgery in popularity. Aiming to obtain the best possible results, scientists have striven to replace damaged articular cartilage with healthy articular cartilage. Previous repair procedures, however, always generated fibrocartilage or, at best, a combination of hyaline and fibrocartilage repair tissue. Autologous chondrocyte implantation (ACI) procedures are cell-based repairs that aim to achieve a repair consisting of healthy articular cartilage. ACI articular cartilage repair procedures take place in three stages. First, cartilage cells are extracted arthroscopically from