Prosthetic Hand Touch Sensation Functions in Real-World Users

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Photograph courtesy of Johan Bodell/Chalmers University of Technology.

For the first time, people with arm amputations can experience sensations of touch in a mind-controlled arm prosthesis that they use in everyday life. A study published April 30 in theNew England Journal of Medicine reports on three Swedish patients who have lived with the new technology for several years.

The patients have each used a mind-controlled neuromusculoskeletal prosthesis in their everyday life for up to seven years, and for the last few years, they also had sensations of touch in the prosthetic hand.

The implant system for the touch-sensitive prosthesis, e-OPRA, is based on the Osseointegrated Prosthesis for the Rehabilitation of Amputees (OPRA) system. The e-OPRA system sends signals in both directions between the prosthesis and the brain, just like in a biological arm.

The research was led by Max Ortiz Catalan, PhD, an associate professor at Chalmers University of Technology, in collaboration with Sahlgrenska University Hospital, University of Gothenburg, and Integrum AB, all in Gothenburg, Sweden. Researchers at Medical University of Vienna and the Massachusetts Institute of Technology were also involved. Integrum AB created the OPRA system.

"Our study shows that a prosthetic hand attached to the bone and controlled by electrodes implanted in nerves and muscles can operate much more precisely than conventional prosthetic hands," said Ortiz Catalan. "We further improved the use of the prosthesis by integrating tactile sensory feedback that the patients use to mediate how hard to grab or squeeze an object. Over time, the ability of the patients to discern smaller changes in the intensity of sensations has improved.

"The most important contribution of this study was to demonstrate that this new type of prosthesis is a clinically viable replacement for a lost arm. No matter how sophisticated a neural interface becomes, it can only deliver real benefit to patients if the connection between the patient and the prosthesis is safe and reliable in the long term. Our results are the product of many years of work, and now we can finally present the first bionic arm prosthesis that can be reliably controlled using implanted electrodes, while also conveying sensations to the user in everyday life."

The prosthesis is self-contained; all electronics needed are contained within the prosthesis, so patients do not need to carry additional equipment or batteries, and it has shown to be safe and stable in the long term. The technology has been used without interruption by patients during their everyday activities, without supervision from the researchers, and it is not restricted to confined or controlled environments.

Force sensors located in the thumb of the prosthesis measure contact and pressure applied to an object while grasping. This information is transmitted to the patients' nerves leading to their brains. Patients can thus feel when they are touching an object, its characteristics, and how hard they are pressing it, which is crucial for imitating a biological hand.

"Currently, the sensors are not the obstacle for restoring sensation," said Ortiz Catalan. "The challenge is creating neural interfaces that can seamlessly transmit large amounts of artificially collected information to the nervous system, in a way that the user can experience sensations naturally and effortlessly."

"Right now, patients in Sweden are participating in the clinical validation of this new prosthetic technology for arm amputation," Ortiz Catalan said. "We expect this system to become available outside Sweden within a couple of years, and we are also making considerable progress with a similar technology for leg prostheses, which we plan to implant in a first patient later this year."

The neuromusculoskeletal implant can connect to any commercially available arm prosthesis, allowing them to operate more effectively.

To see video of the devices in use, visit https://youtu.be/Oaf4NZCFeTM.

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