An interview from the Scientist: "Cartilage is a firm, yet elastic, connective tissue that cushions joints and minimizes friction between bones. It is made up mostly of a matrix of collagen and proteoglycans and lacks nerve cells or blood vessels. In fact, cartilage contains only one cell type, the chondrocyte. A joint injury is often followed by progressive degeneration of cartilage, but there is hope that stem cells injected into damaged cartilage can help repair it. University Hospital Basel tissue engineer Ivan Martin discusses a recent study that sheds light on the mysterious process of cartilage regeneration by tracking labeled, implanted cells using a conventional MRI scanner ... [For treating cartilage injury] there is a very promising, relatively new technique - the use of autologous cartilage cells, or chondrocytes, which are expanded ex vivo and injected into the defective area. Even more recently, people have considered using mesenchymal stem cells, which are the progenitors of chondrocytes. ... We cannot just continue injecting cells and looking two years down the road to see if there is a change or not in the clinical results. We need to have control over the treatment we apply in order to understand the mechanisms of action and to be able to predict with better reproducibility the clinical outcome. This [MRI-based] technique would possibly contribute or provide the technical means to address this important scientific question."