I've heard there's a way to regrow torn cartilage in the knee. Are they using stem cells to do this?

Not yet. Researchers at Johns Hopkins have tried using stem cells to grow into tissue that's like cartilage. They are testing a method injecting fluid filled with stem cells into the joint. The liquid hardens into a stable gel when placed under a special light. Stem cells inside the gel start to multiply and form new cartilage. So far only animals have been used in these studies.

In the meantime, doctors have found two other ways to get cartilage to repair itself. The first is called microfracture. Surgeons use a blunt awl (a tool for making small holes) to poke a few tiny holes in the bone under the cartilage. This causes new tissue, mainly scar tissue, to grow and fill in the holes.

The second is autologous chondrocyte implantation. Normal, healthy cartilage cells are taken out of the knee. They are sent to a special lab where more cells are grown from the original cells. The new batch of cells are put into the joint surface where the damage is located.