It's a question that has captivated sports fans and scientists.

Did a radical stem cell treatment help Gordie Howe recover from a stroke that left him paralyzed on his right side and almost ended his life last year?

A W5 documentary crew teamed up with a top Canadian scientist to find out, taking cameras inside the San Diego company that made Gordie's stem cells and the Mexican clinic where he received treatment.

"I think it's an interesting case. I think it can have a huge impact on people's perception of stem cell research,” says Dr. Duncan Stewart, the scientific director of Regenerative Medicine at the Ottawa Hospital Research Institute.

“I was interested to see what was actually done, what kind of stem cells were used. What really happened here,” he adds.

The Howe family also gave the W5 team unprecedented access to their 87-year old father who is undergoing rehabilitation in Lubbock, Texas. The family even allowed W5 to bring along an American stroke expert to assess Gordie, a man many describe as the greatest hockey player who has ever lived.

"This was an individual who had severe deficits after stroke and shortly after receiving a dose of stem cells had a substantial if not overnight recovery. And an opportunity to look into that a little bit more on my own is, is something I couldn’t resist, " says Dr. Steven Cramer, a neurologist at University of California Irvine.

Did it work?

By all accounts, Mr. Hockey is doing well. In home video he is on his feet, walking, even sweeping and vacuuming.

Gordie had a haemorrhagic stroke Oct. 26, 2014: a blood vessel burst in his brain, killing cells in the thalamus, an area of the brain that controls motor function.

He was unable to move his right arm or leg and as he worsened, doctors had nothing to offer him and only recommended palliative care, his sons Murray and Marty Howe said in an interview with W5.

With nothing to lose, they took him to the Santa Clarita clinic, run by Novastem, a company in Tijuana, Mexico to take part in an experimental stem cell study. A day after his treatment, he was up and walking.

"Absolutely mind blowing. I have been doing medicine for 28 years and I have never seen that in a stroke patient, especially some one going downhill like my dad was," says Murray, who is a radiologist in Toledo, Ohio.

"To me it is clear cut, you have a man on his death bed and he has a treatment and eight hours later he can walk and talk. You put two and two together. I don't see it as placebo effect, " he says.

"This for real," adds Marty, a former professional hockey player himself. "Gordie is a strong man, but I don't think that was it. It was definitely the stem cells that made this happen."

However Gordie's Lazarus-like recovery dubbed "the miracle in Mexico" by some in the media, worries North American scientists who argued here was no proof his therapy made him get better, and that hydration, even a natural rebound could be factors.

Some even called the therapy "snake oil" using “alleged” stem cells. The concern: all publicity and hype around the treatment combined with Gordie’s celebrity could encourage desperate patients to travel to stem cell clinics around the world, a practice called “stem cell tourism”.

By some reports there are now more than 700 clinics, mostly in developing countries. Some are offering stem cell therapies to “cure” a variety of ailments, charging between $20,000 and $50,000.

But in some cases, patients have returned with infections and other complications and with no improvement in their condition. The fear is that the Howe family’s account would send desperate patients abroad.

"One danger is that people will jump to conclusions this is a cure. A panacea and they will all try and book themselves the next flight out when they have this kind of problem to the nearest clinic that offers this service. This could be wasting money, at worst, they may not be getting a therapy that is not safe,” says Dr. Stewart.

But the Howe family says it isn’t promoting stem cell tourism and only made their story public after numerous media requests.

"We felt we had to tell everybody because the last press release, we said Mr. Hockey isn't doing well he is back in the hospital. We don't know how much longer he is going to be with us,” says Murray.

“Then suddenly he is raking and sweeping and goofing around in the back yard. And people ask ‘Why is he doing better?’ and so we decided that at some point, we had to explain what's going on."

Despite the controversy, Dr. Stewart sees Gordie Howe's story as an opportunity to ignite public interest and funding for proper stem cell research.

“We’re well positioned in Canada to do this. We have a lot of expertise in this area. We discovered stem cells. So I think we’re poised to do some very important trials including the kind of trial in the disease that Gordie Howe had in stroke,” says Dr. Stewart.

Scientists have been excited about stem cells since the first discoveries in the field were made in Canada in 1961 by James Till and Ernest McCulloch at the Ontario Cancer Institute in Toronto.

Stem cells have the capacity to become any cell in the body, including brain, blood or skin cells. The most potent type are found in embryos, but they also circulate in our blood and live in tissue like brain, fat and bone marrow and spring into action when we are injured to repair damaged cells.

There are studies underway all over the world to see if researchers can grow stem cells and give them to patients to treat a vast array of illnesses that have no cure, such as diabetes, dementia, spinal cord injuries and stroke.

Stemedica, the company that made the stem cells given to Gordie Howe, is sponsoring its own research: four safety stem cell studies in the United States for treating sun-damaged skin, heart attacks, heart failure and stroke.

They also plan to start more for Alzheimer's, Type 2 diabetes and traumatic brain injuries.

"We don't have all the answers yet obviously but we do have a very, very safe product that's now being pursued in a number of clinical trials in the United States and overseas," says Stemedica CEO Maynard Howe, who has no relation to the Gordie Howe family.

Travels to California, Mexico

Dr. Stewart met with Stemedica's scientists, reviewed their research and toured the company' manufacturing site. It’s an FDA-approved facility with products licenced to be sold for human research around the world.

The stem cells some labelled as snake oil are actually real, says Dr. Stewart.

"That was one of the things I was impressed about. The company has put a lot of effort and resources into their manufacturing procedures. And I think they’re producing a, a high quality stem cell product. So, that part I think is quite strong," he said.

The stem cells are “high quality” but how well do they work?

Dr. Stewart travelled with the W5 crew to Tijuana, Mexico to visit Santa Clarita. It’s a brand new clinic run by Novastem, a company licensed to use Stemedica stem cells.

In December, anesthesiologist Dr. Cesar Amescua injected neural stem cells derived from fetal tissue into Gordie's spine. They travel through the cerebrospinal fluid to the the regions of the brain damaged by stroke, he explains in a demonstration for W5 journalists.

In animal studies, the neural cells migrate to the injured areas and help repair the circuits of the brain. The hope is they will do the same in humans, but the researchers do not know for sure.

Gordie also received an intravenous infusion of up to 90 million mesenchymal stem cells grown from a donor. Scientists believe these cells are a body's workhorses, performing general repairs and reducing dangerous inflammation.

Gordie received his treatment for free, but others pay $30,000 to take part in the Mexican study.

It's called a patient-funded study and it is legal in Mexico, says Dr. Amescua.

The clinic offer no guarantees and doesn’t use the word “cure.”

Gordie had "an extraordinary response to a treatment but don't expect every patient will have the same result,” says Dr. Amescua.

“Some patients probably will get better, some won't,” says Dr. Amescua.

He has treated seven other stroke patients but he can’t disclose how they are doing due to the ongoing clinical study, and to protect patient privacy.

"It's in Mexico for a reason,” says Dr. Stewart, speaking about the Santa Clarita clinic.

“In Mexico there's much less regulation for stem cell delivery and I was told in the clinic, it's allowed by Mexican law, you can give stem as a therapeutic product if the doctor feels its warranted."

The clinic says it is conducting a “clinical trial,” but Dr. Stewart says the study lacks proper follow-up procedures that are required in Canada and the U.S.

Patients go home and are seen by their own doctors, if at all. Important brain scans, blood tests may never get done, he adds.

Because insufficient data is collected, scientists will probably never know “whether the therapy works or not,” says Dr. Stewart.

"My sense is they're well intentioned. I don't think they're very experienced or well trained in the principal of clinical trials."

The bottom line: Gordie’s case is intriguing, but it tells us very little.

“In medicine we know that the strangest things can happen. And one case is an anecdote, that’s all it is. It can never prove anything,” Dr. Stewart says.

How is Howe doing?

Since the treatment in December, Gordie has been undergoing therapy at home and in a clinic. We were allowed to film a session in late March.

During therapy, Gordie catches balls, climbs stairs and even dances with his therapist. The hockey star has dementia and a back injury, but he keeps up the pace for more than an hour.

Dr. Cramer examines Gordie after the session. The hockey star’s grip is strong and his ability to move his feet is near normal, he says.

Gordie even signs his autograph with his right hand which was paralyzed months earlier. He writes slowly but the famous name is legible.

Dr. Cramer concludes his recovery is "impressive."

"He had pretty much complete paralysis of all the muscles on the right side of his body and when I saw him today he had very mild motor deficits. He had near-complete range of motion of joints," explains Dr. Cramer.

"It is a remarkable degree of motor improvement for anybody with that severe severe of stroke and when you mix in the fact that it was towards the end of his ninth decade, it's all the more remarkable," he says.

Dr. Cramer also say Howe’s physio and occupational therapy could have played a role, or we may be witnessing a spontaneous improvement which occurs in some patients in the first three to six months after a stroke.

His recovery may even be due to what Dr. Cramer calls the "piss and vinegar gene," a fighting spirit or drive to survive and return to normal, which Gordie has in abundance.

It is possible that stems cells could have helped, too. The fact Gordie's recovery came so soon after receiving the stem cells is interesting.

“Some of the timing seems like a bit of a coincidence,” says Dr. Cramer

But Dr. Cramer is quite cautious. “You have to be very careful about drawing any firm conclusions from what we see here. However, what we see here has some exciting potential," he says. "If his improvement is in anyway attributable to these stem cells, it’s very exciting. It raises hope."

Dr. Cramer points to a Stanford University study which suggests two female stroke patients improved dramatically after receiving donated bone marrow stem cells. Both women were able move their arms and legs the day after their treatment, even though they had their stroke two years earlier and were severely disabled.

Another recent study presented at the European Stroke Organization Conference in Glasgow reported that in a preliminary study of 11 male stroke patients, human neural stem cells given as an injection directly into the brain improved function in some patients with no related side effects.

If anything, Gordie’s story is a wake-up call for accelerated research and money for more well-designed studies to answer urgent questions about stem cells and their potential to cure disease, says. Dr. Cramer.

"We don't know the risk and we don't know the benefits yet. So, good that you're excited about it, write your Senator or whatever the Canada thing is…and get these trials funded.

“I do not suggest to my patients to go outside of the U.S. and do what was done here," Dr. Cramer says, adding that he plans to start his own study with Stemedica stem cells.

Unfortunately, there are still not enough studies which leads to patient frustration and stem cell tourism.

“We get dozens of information requests each week from desperate people asking ‘How do they get into a trial?’” says James Price, CEO of the Canadian Stem Cell Foundation.

Aware of the growing demand for new therapies, the Canadian Stem Cell Foundation recently launched a campaign on behalf of scientists across Canada.

It is asking for more than $1.5 billion in corporate and government funding over the next decade “for safe clinical trials in Canada as soon as possible,” says Price.

“We get calls all the time from stroke victims and the thing is if we can get the trials, we can get the research done, I am positive it is going to show that this is a great help to the public,” says Marty.

In the meantime, the Howe children say they remain convinced the stem cell therapy their father received in Mexico improved his quality of life. Some have actually invested in the stem cell company.

Dr. Murray says Howe is also hoping to start trials with the stem cells to treat brain injuries at his hospital in Ohio.

What’s more, his family is hoping to bring their father to Mexico for another stem cell treatment this summer.

“Our lives are an open book. I mean our parents again have always taught us that, you know, we – we belong to the public. With my father we’ve tried to be as open as we can and as transparent in terms of his treatment and how he’s doing,” says Murray.