Einhorn drew bone marrow from the man's pelvic bone with a needle, condensed it to about four teaspoons of rich red liquid, and injected that into his ankle.
Four months later the ankle was healed. Einhorn, chairman of orthopedic surgery at Boston University Medical Center, credits "adult" stem cells in the marrow injection. He tried it because of published research from France.
Einhorn's experience isn't a rigorous study. But it's an example of many innovative therapies doctors are studying with adult stem cells. Those are stem cells typically taken from bone marrow and blood - not embryos.
For all the emotional debate that began about a decade ago on allowing the use of embryonic stem cells, it's adult stem cells that are in human testing today. An extensive review of stem cell projects and interviews with two dozen experts reveal a wide range of potential treatments.
Morley Safer reported for "60 Minutes" this summer on the rapidlywhere cells in the human body are manipulated into regrowing damaged tissues.
Researchers have created beating hearts, ears and bladders using stem cells. Biotech companies and the Pentagon have invested hundreds of millions of dollars in research that could profoundly change millions of lives.
Adult stem cells are being studied in people who suffer from multiple sclerosis, heart attacks and diabetes. Some early results suggest stem cells can help some patients avoid leg amputation. Recently, researchers reported that they restored vision to patients whose eyes were damaged by chemicals.
Apart from these efforts, transplants of adult stem cells have become a standard lifesaving therapy for perhaps hundreds of thousands of people with leukemia, lymphoma and other blood diseases.
"That's really one of the great success stories of stem cell biology that gives us all hope," says Dr. David Scadden of Harvard, who notes stem cells are also used to grow skin grafts.
"If we can recreate that success in other tissues, what can we possibly imagine for other people?"
That sort of promise has long been held out for embryonic stem cells, which were first isolated and grown in a lab dish in 1998. Controversy over their use surrounded the 2001 decision by former President George W. Bush to allow only restricted federal funding for studying them.
Proponents over the past decade have included former first lady Nancy Reagan and actors Michael J. Fox and the late Christopher Reeve. Opponents object that human embryos have to be destroyed to harvest the cells.
Embryonic cells may indeed be used someday to grow replacement tissue or therapeutic material for diseases like Parkinson's or diabetes. Just on Friday, a biotech company said it was going ahead with an initial safety study in spinal cord injury patients. Another is planning an initial study in eye disease patients later this year.
But in the near term, embryonic stem cells are more likely to pay off as lab tools, for learning about the roots of disease and screening potential drugs.
Observers say they're not surprised at the pace of progress.
As medical research goes, the roughly 10 years since the embryonic cells were discovered "is actually a very short amount of time," said Amy Rick, immediate past president of the Coalition for the Advancement of Medical Research. The group has pushed for embryonic stem cell research for about that long.
Hank Greely, a Stanford University law professor who works in bioethics and has followed stem cells since the 1990s, said: "Give it another five years and I'll be surprised if we don't have some substantial progress" beyond initial safety studies.
The Pro-Life Secretariat of the U.S. Conference of Catholic Bishops continues to oppose embryonic work. Deirdre McQuade, an official there, said that compared to adult stem cell research, work on embryonic cells is proving "fruitless."
Adult cells have been transplanted routinely for decades, first in bone marrow transplants and then in procedures that transfer just the cells. Doctors recover the cells from the marrow or bloodstream of a patient or a donor, and infuse them as part of the treatment for leukemia, lymphoma and other blood diseases. Tens of thousands of people are saved each year by such procedures, experts say.
But it is harnessing these cells for other diseases that has encouraged many scientists lately.
In June, for example, researchers reported they had restored vision to people whose eyes were damaged from caustic chemicals. Stem cells from each patient's healthy eye were grown and multiplied in the lab and transplanted into the damaged eye, where they grew into healthy corneal tissue.
A couple of months earlier, the Vatican announced it was funding adult stem cell research on the intestine at the University of Maryland. And on Friday, Italian doctors said they'd transplanted two windpipes injected with the recipients' own stem cells.
But these developments only hint at what's being explored in experiments across the United States.
Much of the work is early, and even as experts speak of its promise, they ask for patience and warn against clinics that aggressively market stem-cell cures without scientific backing.
Some of the new approaches, like the long-proven treatments, are based on the idea that stem cells can turn into other cells. Einhorn said the ankle-repair technique, for example, apparently works because of cells that turn into bone and blood vessels. But for other uses, scientists say they're harnessing the apparent abilities of adult stem cells to stimulate tissue repair, or to suppress the immune system.
"That gives adult stem cells really a very interesting and potent quality that embryonic stem cells don't have," says Rocky Tuan of the University of Pittsburgh.