Study finds AR helps reduce phantom limb pain in people with amputations

By Heather Mack
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For people who have had an amputation, the phantom pain they experience in the missing limbs is as real as any other pain. However, treating pain at a source that is no longer there has long baffled scientists, and many existing therapies, including the use of implantable nerve stimulators or medications, offer no relief for many phantom pain sufferers.

But a new study shows augmented reality may be a viable option to treat this puzzling phenomenon. Through a mix of myoelectric sensors, artificial intelligence and virtual reality, patients are able to visualize the arm as real again, thus allowing them to reactivate areas of the brain that were used before and, somehow, reducing chronic pain.

At the Chalmers University of Technology in Sweden, a clinical trial using machine learning and augmented reality alleviated a significant level of phantom limb pain in 14 patients with amputated arms. Patients reported having no relief with any other treatments, but after 12 sessions with the AR system saw a reduction in pain by approximately 50 percent. 

“We selected the most difficult cases from several clinics,” Dr. Max Ortiz Catalan, who developed the AR system, said in a statement. “We wanted to focus on patients with chronic phantom limb pain who had not responded to any treatments. Four of the patients were constantly medicated, and the others were not receiving any treatment at all because nothing they tried had helped them. They had been experiencing phantom limb pain for an average of 10 years.”

The AR system, called phantom motor execution, consists of using muscle signals from the amputated limb to control augmented and virtual environments. Electrodes are placed on the skin to detect signals in the muscles that controlled the now-missing limb, and artificial intelligence algorithms then translate the signals into movements of a virtual arm in real-time. A virtual arm is superimposed on the screen, resulting in the perceived phantom arm as being “brought to life.”

Along with the pain reduction, patients also reported a lessening of intrusion of pain in sleep and daily activities, and two of the four patients who were on analgesics were able to reduce their doses by 81 percent and 33 percent, the researchers found.

The study, which was published in the Lancet, was carried out in collaboration with three hospitals in Sweden and one in Slovenia. Ortiz Catalan said it could open up the door to future clinical treatment opportunities as well as shed light on what’s going on in the brain during phantom pain episodes.  

“The results are very encouraging, especially considering that these patients had tried up to four different treatment methods in the past with no satisfactory results,” Ortiz Catalan stated. “In our study, we also saw that the pain continuously decreased all the way through to the last treatment. The fact that the pain reduction did not plateau suggests that further improvement could be achieved with more sessions.”

The AR technology is available in two modalities – an open source research platform and a clinically friendly version that is being commercialized by Integrum, a Gothenburg-based company. The researchers believe the technology could also be applied to other neurological conditions that require movement rehabilitation, such as a stroke. For now, the team will look to scale up the study for amputees.

“Our joint project was incredibly rewarding, and we now intend to go further with a larger controlled clinical trial,” said Ortiz Catalan. “The control group will be treated with one of the current treatment methods for phantom limb pain. This time we will also include leg amputees. More than 30 patients from several different countries will participate, and we will offer more treatment sessions to see if we can make the pain go away completely.”