Most of the work to date on the relationship between aging changes at the cellular level and the development of OA has focused on the articular cartilage. Given the similarities between chondrocytes and meniscal cells these studies probably also relate to aging in the meniscus but more studies need to be done in that specific tissue. Normally there is little to no cell turnover in adult articular cartilage52 and so chondrocytes are thought to be long-lived cells and as such can accumulate age-related changes over many years. In many tissues, senescent cells can be replaced by differentiation of cells from a local pool of progenitor cells but in adult articular cartilage it is not clear if such a pool exists. Recent studies have challenged the notion that cartilage does not contain progenitor cells but these studies were performed with either bovine tissue from very young animals53 or OA tissue54, the latter of which might have included cells from other tissues such as the synovium or bone marrow which can make their way to the cartilage when it is severely damaged. Even if there is a local pool of progenitor cells, they do not appear to be capable of replacing senescent, damaged, or dead cells in the articular cartilage.