[Present status and perspective of articular cartilage regeneration]

Because the capacity of articular cartilage for repair is limited, defects are a major clinical problem, and there is at present no satisfactory clinical technique to regenerate cartilage defects. Current clinical practice involves the bone stimulation technique, which breaks subchondral bone to facilitate cartilage repair from bone marrow derived cells and cytokines. This consists of multiple perforations, abrasions, and micro-fractures. However, with this procedure, cartilage defects are repaired with fibrocartilage, which is known to be biochemically and biomechanically different from normal hyaline cartilage and degeneration occurs in the reparative tissue. Autologous chondrocyte implantation (ACI) for repair of human articular cartilage was reported in 1994, and approved by the USA Food and Drug Association in 1997. This procedure has been performed for more than 20000 people all over the world, but its effectiveness is still controversial. Mosaic plasty was explored in the 1990s. Using this procedure, we can repair defects with hyaline cartilage, but the donor site morbidity is unsolved. To explore a new method for cartilage repair, we transplanted autologous culture-expanded bone marrow mesenchymal cells into articular cartilage defects. Clinical symptoms were improred but the repair cartilage was not hyaline cartilage. Further improvement is required. Many investigations have been made in the search for better means of repair, including gene transduction and the addition of growth factors during cell culture. In addition to bone marrow mesenchymal cells, synovial cells, adipocytes, muscle cells, etc. have been evaluated.