Hyaline articular cartilage constitutes the principal workingcomponent of the synovial joints, and in adults it containsneither blood vessels nor nerves1. Cartilage provides diarthrodialjoints with a remarkably resilient and long-lasting glidingsurface, with a coefficient of friction approximately one fifththat of ice on ice. It is capable of self-renewal and self-lubricationand works well under a load. In short, it is an almost perfectmachine, with mechanical properties that are far better thanthose of the polished metal on high-density polyethylene thatis used in total joint-replacement systems.