@Clairdelune - I think the article explains how chondrocytes, a part of cartilage, repairs and nourishes this tissue. But, for some reason, the cartilage becomes so damaged that chondrocytes can no longer repair the damage. And the joints become more and more diseased.
Research in stem cell transplants, as the article says, is used in cases of a severe injury. Maybe this works well on a younger person, but I've heard that more research is needed on stem cell transplants to repair cartilage damaged by arthritis. It is not being used at this time.