Augmented Reality Relieves Phantom Limb Pain


Ortiz Catalan demonstrates the augmented virtual reality environment in his new Biomechatronics and Neurorehabilitation Laboratory at Chalmers. Photograph courtesy of Anna-Lena Lundqvist.

Max Ortiz Catalan, PhD, an assistant professor in the Department of Signals and Systems at Chalmers University of Technology (Chalmers), Gothenburg, Sweden, has developed a novel method of treating phantom limb pain using machine learning and augmented reality. This approach has been tested on 14 people with upper-limb amputations who have chronic phantom limb pain and who found no relief by other clinically available methods. The new treatment, invented by Ortiz Catalan several years ago and further developed with his multidisciplinary team since then, reduced the participants' pain by about 50 percent, reports a clinical study published in The Lancet.

Ortiz Catalan calls the new method phantom motor execution. It uses muscle signals from the residual limb to control augmented and virtual environments. Electric signals in the muscles are picked up by electrodes on the skin. Algorithms translate the signals into movements of a virtual arm in real time. The patients saw themselves on a screen with the virtual arm in place of their missing arm. Thus, the perceived phantom arm is brought to life by a virtual representation that the patients can see and control. This allows the patient to reactivate areas of the brain that were used to move the arm before it was amputated, which might be the reason that the phantom limb pain decreases. No other treatment for phantom limb pain generates such a reactivation of these areas of the brain with certainty, according to the study's authors. The research not only creates new opportunities for clinical treatment, but it also contributes to the understanding of what happens in the brain when phantom limb pain occurs.

The patients were treated with the new method for 12 sessions. At the last session, the intensity, frequency, and quality of pain had decreased by about 50 percent. The intrusion of pain in sleep and in activities of daily living was also reduced by half. In addition, two of the four patients who were on analgesics were able to reduce their doses by 81 percent and 33 percent.

"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 said. "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."

Ortiz Catalan said the research group will continue its work with a larger controlled clinical trial that includes people with lower-limb amputations. "The control group will be treated with one of the current treatment methods for phantom limb pain.... 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."

The technology for phantom motor execution is available in two modalities-an open-source research platform, and a clinically friendly version in the process of being commercialized by the Gothenburg-based company Integrum. The researchers said they believe that this technology could also be used for other patient groups who need to rehabilitate their movement capability, for example after experiencing a stroke, sustaining nerve damage, or injuring a hand.

Editor's note: This story was adapted from materials provided by Chalmers University of Technology.