Dr. Joel Baumgartner readily admits that it may be years before any insurance company pays for this treatment.

And that's a point of pride for the family physician in Sartell, Minn. "I would say yes, I'm a pioneer," he said.

Baumgartner, 39, is one of a small but growing number of doctors who are offering stem cell therapy for common medical conditions -- even though experts say such treatments have yet to be proven safe and effective.

On the website of his clinic, Rejuv Medical, Baumgartner advertises stem cell therapy as an alternative to surgery for knee pain, back pain and other orthopedic problems, inviting patients to "Unleash the power of your own stem cells!"

In other parts of the country, some clinics are offering stem cells as "anti-aging" therapies, or for serious diseases such as multiple sclerosis and Parkinson's disease, said Leigh Turner, a medical ethicist at the University of Minnesota who is tracking the trend.

"They're on the Internet making a whole series of claims," Turner said. "It looks to me like there's been a rush out of the laboratory into the clinic, and it's happened earlier than it should have."

The problem, says Paul Knoepfler, a stem cell researcher at the University of California, Davis, is that "the science is just not there."

The trend has triggered a simmering debate in the medical field and at least one federal court case over who should decide when a treatment that basically uses a patient's own cells is ready for prime time.

In medicine, almost everyone agrees that stem cells are one of the most exciting areas of research. The cells are the chameleons of the body, with the ability to turn into various types of human tissue. An international race is on to find ways to harness those cells to cure disease and heal injuries.

"We're working on it," said Dr. Rafael Sierra, an orthopedic surgeon and researcher at the Mayo Clinic's Center for Regenerative Medicine. But in general, he said, it's "certainly not ready to be done on patients yet." There are too many unanswered questions, he said, including how to make sure stem cells do what they're supposed to do, without causing harm.

But Baumgartner and other doctors say the evidence is encouraging enough already to offer the treatment as an option to patients, much like other elective procedures.

"Health care is becoming what's best for the patient, not what insurance covers," Baumgartner said. "If they decide this is something they want, why should this be something they can't have?"

'I wanted to be the guinea pig'

Baumgartner started offering the stem cell therapy in May, using a method developed by a Colorado clinic and its company, Regenerative Sciences. The company has been locked in a four-year court battle with the U.S. Food and Drug Administration, which won an injunction in July to stop Regenerative from selling an unapproved drug made with stem cells. The company has vowed to appeal.

The legal battle, however, did not apply to the treatments at Baumgartner's clinic, which offers "same-day" procedures that, he and others say, aren't regulated by the FDA.

Baumgartner spent several weeks training in Colorado to learn the technique. So far, he said, he's given the treatment to "seven or eight" patients, including a clinic employee. The charge per patient: about $4,000 for the stem cells alone, he said.

Ernie Rodriguez of Baraboo, Wis., knew the treatment was experimental. But, he said, "I wanted to be the guinea pig." At 59, he said, he had been living with "bone-on-bone" pain for more than four years and had been told he'd need a partial knee replacement.

After reading about the stem cell treatment online, he made an appointment at Baumgartner's clinic in early June.

The treatment typically spans three days, according to Baumgartner. First day: blood draws and preliminary injections. Second day: They take bone marrow from the hip, put it in a centrifuge to separate the stem cells and inject those cells into the damaged joint. Third day: More injections, including a natural solution that acts like a fertilizer, Baumgartner says. Afterwards, the patient wears a brace for weeks or months to help with the healing.

Two months after his procedure, Rodriguez said, "I can get up and it doesn't hurt. I can jump up and it doesn't hurt." The price? "About $7,000," he said. "But I tell you what, I would do it again."

'A lot of case studies'

Baumgartner says he's careful not to overpromise the benefits of stem cells, and his website includes the caution that the "clinical effectiveness has not yet been established."

Still, he says, "I'd say there's a lot of proof." Not traditional clinical trials, he said, but "a lot of case studies" by Regenerative Sciences, the company that developed the treatment.

The stem cell therapy has been performed on about 1,500 patients so far, according to Dr. Chris Centeno, founder of Regenerative Sciences. Seven clinics (including Baumgartner's) have been trained to provide it across the country.

Centeno and his colleagues have published a number of studies showing that the treatment shows promise, including one report on 135 knee patients, in which about 60 percent reported improvement. Some of the published studies, however, are on only one patient or just a handful. In 2011, a study of six patients concluded simply that "the results ... support the hypothesis" that stem cells "may be an alternative" to surgery.

Many stem cell researchers say that while the treatment is promising, the evidence is thin.

"That's I think one of the big criticisms," said Knoepfler, of the University of California, Davis. "There's just none of that robust clinical trial data." He notes that such studies are difficult and expensive, but without them, the proof is missing.

The International Society for Stem Cell Research has warned that it's "very concerned that stem cell therapies are being sold around the world." In its "Patient Handbook on Stem Cell Therapies," it cautions that the treatments "are nearly all new and experimental" and may not work.

To Knoepfler, who does research on stem cells and cancer, there's an even bigger concern: safety. "If you take aspirin and you have a bad reaction, you just stop taking it and it goes away," he said. "But stem cells are alive." Once injected, he said, they can grow or drift to other parts of the body. "It's a little scary."

Centeno, meanwhile, has published several follow-up studies showing no increase in cancer among his stem cell patients.

Still, a number of orthopedic surgeons predict it will be years before stem cell therapy becomes routine.

"I think we live in an impatient society where people want answers sooner than that," said Dr. Allan Mishra, of Menlo Park, Calif., a spokesman for the American Academy of Orthopaedic Surgeons. That's one reason, he said, that famous athletes such as Kobe Bryant have turned to alternative treatments, sometimes overseas.

"I do think [stem cells] will provide some of those answers." Mishra said. "We are not there just yet."

Maura Lerner • 612-673-7384