Three years ago, Michael Rix was taking 250 milligrams of codeine a day and waking up in the middle of the night due to extreme pain in his left hip.

Rix, who was 42 at the time, had taken up marathons and was training around his hometown of Sussex, England. He stubbornly ran through the pain, logging between 100 and 120 miles a week, even as it became more acute. Then he woke up one morning and found himself incapable of reaching down to put on his socks.

He paid a visit to orthopedic surgeon Kerry Acton at the Royal Surrey County Hospital in Guildford, and was told that severe osteoarthritis in his left hip meant that he would need a total hip replacement.

The diagnosis didn’t come as a shock — but he was surprised by what Acton said next.

“I was expecting him to say, after hip replacement, no more running nor more competition,” Rix recalled to Seeker over the phone. “But instead he asked me, what would you like to do? I said, in an ideal world, I’d love to get back to sport — maybe not a marathon, but triathlons. He said, ‘Yeah, we can do that.'”

Orthopedic surgeons are increasingly delivering promising news to patients who in previous years might not even have been considered candidates for joint replacement. Such surgeries were usually reserved for people over the age of 60, since the assumption was that the active lifestyles typical of younger people would inevitably break down the artificial joint and cause it to fail.

Today, several research fronts are revolutionizing knee and hip replacements to the point where the joints are practically becoming bionic, from 3-D printed implants to concept technologies that grow entire joints from stem cells.

The big trick behind these advances is recreating the durability of a natural joint in one that is manufactured, while also fooling the human body into believing that it’s home-grown.

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Rix received an implant called the Furlong Evolution, which features a special ceramic coating that mimics a natural mineral present in human bone. The material triggers a biological bond to form between the implant and the patient’s own bone, ensuring that the replacement lasts longer — hopefully for life.

Rix’s implant bonded so well that three months after his surgery, he beat out 105 fellow competitors to win a local sprint triathlon. Now 45, he has competed for Team Great Britain in the last two European and World Duathlon Championships, winning a silver medal in his age group at the 2015 Worlds in Adelaide.

“I have no pain,” said Rix, who had just returned home after a hilly, 10-mile run.

The complete lack of pain is a promising sign that Rix’s hip replacement could last a lifetime. But if it should wear out, a future option might be a biological replacement grown from his own stem cells.

Farshid Guilak, a professor of orthopedic surgery at Washington University School of Medicine in St. Louis, has been working on methods to coax stem cells to develop into new joint cartilage to repair joints. The aim is to someday form entirely new knee and hip joints from stem cells.

Guilak and his team have developed a specially woven “scaffolding” that is designed to fit over a person’s joint.

“We have a machine — it looks like a loom,” he explained. “It weaves 600 fibers into a 1-millimeter layer.”

The machine at at Washington University School of Medicine in St. Louis that weaves scaffold for building cartilage from stem cells. Courtesy: Farshid GuilakThe intricately woven scaffold is then seeded with stem cells taken from a patient’s own fat, which can be made to turn into cartilage cells using what Guilak called a “cocktail of proteins.” The idea is to implant it within the patient and have the stem cells develop into bone and cartilage cells in and around the scaffold. The body would naturally absorb the sheath and the patient would be left with a biologically grown joint.

“The scaffold is designed as a tough 3-D fabric,” Guilak said. “So it can withstand the pressures of the joint as the new, biological cartilage is forming in the body.”

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Guilak’s team is still working to perfect this new method of repairing knee joints.

“We have implanted these in large animals — dogs — and so far the technology is looking very promising,” he said. He and his team are hoping to eventually program the stem cells to release anti-inflammatory compounds at the joint when triggered by an antibiotic.

Others in this field are using donor grafts of bone and cartilage. A team led by Brett Crist, an orthopedist at the University of Missouri School of Medicine, is interested in using large, size-matched grafts of donor bone with beveled edges to fit over damaged joints. So far the tests have gone well in dogs.

“By using one large graft, we reduced the number of seams for a smoother functioning joint,” Crist said in a press statement. “Beveling the edges also created a better fitting repair that was less prone to cell death during implantation.”

3-D printing presents another way of ensuring a better fit when it comes to crafting artificial joints. A line of 3-D printed joints is already on the market and in use. ConforMIS knee implants are customized to each patient based on size and shape measurements taken from a CT scan of a person’s damaged knee.

“Hospitals have started to skew toward 3-D printing as a more viable and efficient model,” said Ben Holmes, CEO of Nanochon, a company that is working to improve 3-D knee replacement joint technology. “It produces better outcomes. You can make a more minimally invasive implant that has less of a long-term problem.”

Holmes, who has a PhD in mechanical engineering, is working with bioengineer Nathan Castro on developing biomaterials for 3-D printing that share the mechanical properties of bone and cartilage and encourage stem cell growth and repair. That way the human body is less likely to resist a new knee or hip joint when it’s introduced into the body.

The materials of Nanochon’s implant are made up of specially designed microstructures.

“The shapes we’re printing are inspired by biological systems,” Holmes explained. “By mimicking the combination of different biological architectures, you can trick stem cells into thinking they’re in a certain part of the body.”

With more than a million joint replacement surgeries being done annually in the United States alone, the bet is that there will be no shortage of new customers lining up to try these cutting-edge implants.

Rix believes the evidence is clear that younger, active people like himself can benefit from emerging orthopedic technologies. Since his triathlon victories, he has become something of a representative for younger joint replacement candidates and meets periodically with orthopedic surgeons to talk about his experience.

“After hearing my story they start to say, ‘You know what, maybe we should start seeing what we can do for our younger patients,'” Rix remarked. “There’s a shift of thinking underway where doctors are realizing the technology is there, and they can make a difference in their patients’ lives.”

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