UT Dallas researchers use virtual reality to help amputees with phantom limb pain

For a month, Dean Peterson put on virtual reality glasses every morning and night to help him sleep. Once a heavy sleeper, he had not slept well since his lower left leg was amputated in 2005.

The carpenter and former Navy medic tossed and turned in bed, kept awake by pain where his lower leg should be. The feeling known as phantom pain was manageable with the distractions of the day, but the stillness of the night made it hard to ignore.

Sometimes the brain sends signals to a missing limb, causing sensations such as itching or cramping, but there is no way for the amputee to relieve this feeling. Researchers at the University of Texas at Dallas developed the software to help people with limb loss trick their brains into believing the missing limb is still there and can be moved without discomfort.

Looking at the VR screen, Peterson saw himself using both legs, which he used to play for games like popping virtual bubbles with his feet or tapping colorful moving circles.

After a few weeks of using the technology called the Mixed Reality System for Managing Phantom Pain, or Mr. MAPP, Peterson noticed he was falling asleep faster. It worked so well that he didn’t want to return the technology at the end of his studies.

“I fall asleep easier now than I used to,” Peterson said. “I’ve already told them to sign me up when they’re ready for the next phase of testing.”

Mr. MAPP is a modern take on mirror therapy, a tool that has been used for decades to help amputees visualize their missing limbs and minimize the pain that occurs when the brain tries to relay nerve signals to part of the limb to send a body that is no longer there. According to the Cleveland Clinic, an estimated 80% of them suffer from phantom limb pain.

Balakrishnan Prabhakaran and his team at UT Dallas are still tinkering with the device, but the computer science professor said Mr. MAPP has the potential to offer amputees an even more realistic therapy option that could reduce the need for medical painkillers.

Prabhakaran worked with the Veterans Affairs North Texas Health Care System to develop the therapy and pilot it in 12 patients at the Dallas VA Medical Center. For four weeks, patients used a laptop, camera and VR headset to create a 3D model of their missing limb.

The software contains three exercises that require the leg to perform different movements. These exercises come in the form of games, and the software tracks the number of successfully completed tasks, like popping bubbles or pressing pedals.

One of the games plays a sound each time the patient hits a virtual colored circle on the floor.

“That’s part of the motivation for this one. You push a button on the floor and it makes a little sound, and that’s really fun,” Peterson said.

Peterson and the other study participants gave the UT Dallas team extensive feedback on what worked and what didn’t. He found that playing the game in shorts and barefoot was more effective because he saw “flesh and blood,” which made the games feel more real.

Mr. MAPP is easy to use, Peterson said, despite never trying a VR system before. The biggest challenge was keeping his pup off the machine during his exercises.

Researchers are still working on some bugs in the software and trying to make it as appealing as possible. Yu Yen Chung, a computer science Ph.D. Candidate working on the project redesigned the camera setup to allow patients to see themselves in first-person rather than having to look at themselves as if in a mirror.

Being able to look down and see both legs can help the body communicate better with the brain, Chung said. First-person perspective has not yet been rolled out to patients, although the team intends to test it soon.

Despite the excitement surrounding the technology’s success, Peterson said he was cautious about telling other amputees in the close-knit limb-loss community about his participation in the study for fear of spurring their hopes.

While there are other treatments for phantom limb pain, ranging from mirror therapy to prescription pain relievers to spinal surgery, the results have been mixed and can even be dangerous. Peterson has previously tried mirror box therapy but found no relief.

For some people, the pain can be debilitating.

“It’s something very real, just like, let’s say, hitting your finger with a hammer and experiencing that kind of pain. Phantom limb pain can be as real as any of these painful sensations for certain individuals without the mechanism or ability to do anything about it,” said Jared Howell, director of the Center for Prosthetic and Orthopedic Care at Baylor College of Medicine.

Highly addictive opioid medications, sometimes prescribed to relieve phantom limb pain, can come at a high cost. A February study of more than 2,000 below-knee amputees found that nearly 55% were taking opioids at the time of their surgery, and nearly 45% had been found to have used opioids for a long time.

“The opioid crisis is really a threat,” Prabhakaran said. “The problem with the way the drug works is that it rewires your brain. And in this case, we’re not rewiring our brains. We trick the brain, but we don’t wire it in a way that’s harmful.”

One patient in the study reported that he stopped taking medication for the pain after using Mr. MAPP. Whenever he felt the urge to take the drugs, he would go and play the game, Prabhakaran said.

“We felt really, really good because so many people are getting addicted in the opioid crisis,” Prabhakaran said. “If we can do something about this crisis, then we should do it.”

UT Dallas and Veterans Affairs secured a provisional patent for Mr. MAPP with hopes of completing the full patent trial in late winter or early spring of 2023. The team is already working to find a partner to license the technology and bring it to market as early as next year.