The researcher says it wouldn't make the joint like new, but it would roll back the clock, so that the painfully arthritic knees of a 70-year-old might become more like the pretty-good knees of a 60-year-old.

More research is needed to see if Forteo would be effective in humans, and safe. Osteoporosis patients get a warning of one possible risk. Studies of Forteo in rats have found the drug increases the risk of a rare bone cancer, osteoscarcoma. But studies of other animals, including primates, have not confirmed the rat finding. Still, to be on the safe side, Forteo is not prescribed for people with a history of cancer.