The following report by medical editor Marilyn Brooks first aired on Channel 4 Action News at 5 p.m. on Feb. 2, 2006.

---

Researchers say a new approach to cartilage repair may one day lead to a treatment for everything from sports injuries to crippling arthritis and osteoarthritis.

They're 12-week-old rats -- and they're special. Twenty-four weeks ago, they had knee joint damage -- but not anymore. It was repaired by genetically engineered muscle-derived stem cells.

"This is why we are so excited -- because not only do we have a treatment, a potential treatment, but a treatment that can survive a very long time," said Dr. Johnny Huard, director of the Growth and Development Lab at Children's Hospital.

One day, Huard's research may help athletes, because muscle stem cells can turn into any tissue and become bone cells, cartilage, even heart cells.

For their study, researchers took muscle-derived stem cells from rats, genetically modified them to express bone muscle morphogenetic protein -- or BMP -- and used it to treat the rat's damaged knee cartilage.

"We found that those cells can repair the articular cartilage, but we have a long term persistence. We found that those cartilages we're making can survive and can remain there for up to 24 weeks," said Huard.

Since the stem cells come from the patient's own muscle, doctors say there's no worry of rejection.

The research will take at least three years, maybe more. And it may seem hard to believe, but the very process that is now helping tiny creatures get around without pain may very well, in the future, help millions of people get around without pain.

That means damaged cartilage in amateur and professional athletes may get a second chance.

"The goal would be to take a muscle biopsy from those athletes, isolate those cells and use them to repair their own cartilage," said Huard.

Huard's research can't help Jerome Bettis now, but in the future:

"Maybe after he does that [retires from football], he will come and we will tune him up," said Dr. Freddie Fu, chairmen of Orthopedic Sports Medicine.

Researchers say it's going to take a couple of years to begin human trials.