Updated:04/29/2020 10:00 p.m.
For the first time, three people who had had an amputation of their arm can have the sensation of ‘touch’ through a prosthesis located in their limb that is controlled by the mind. A study published today in The New England Journal of Medicine presents three Swedish patients who have lived, for several years, with this new technology, one of the world‘s most integrated human-machine interfaces.
The breakthrough is unique: Patients have worn a mind-controlled prosthesis in their daily lives for seven years. In recent years, they have also had a new function: the sensation of touch in the prosthetic hand. This is a new concept for artificial limbs, which are called neuromusculoskeletal prostheses, since they are connected to the user’s nerves, muscles and skeleton.
“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,” he explains. Max Ortiz Catalan, associate professor at Chalmers University of Technology and study coordinator.
This researcher explains that the use of the prosthesis has been improved by integrating the “tactile sensory feedback” that patients use to mediate how difficult it is to grasp or squeeze an object. “Over time, the ability of patients to discern smaller changes in the intensity of the sensations it has gotten better », points Max Ortiz Catalan.
In his opinion, the most important finding of this study has been to demonstrate that this new type of prosthesis is a “clinically viable replacement for a lost arm”. It doesn’t matter, he continues, “how sophisticated the neural interface is, a real benefit to patients can only be provided 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 which can be controlled in a way using implanted electrodes, while transmitting sensations to the user in everyday life. “
Since the prostheses were implanted, patients have used them daily in all their professional and personal activities.
Ortiz stresses that this new concept of neuromusculoskeletal prostheses is unique, as it offers several different characteristics that have not been presented together in any other prosthetic technology in the world. For example, it has a direct connection with the nerves, muscles and skeleton of a person; he is mentally controlled and offers sensations; It is autonomous since all the necessary electronic components are contained within the prosthesis, so patients do not need to carry additional equipment or batteries, and it is safe and stable in the long term.
And how does the touch feel again? According to this researcher this has been possible thanks to the stimulation of the nerves that are connected to the biological hand before amputation. Force sensors located on the thumb of the prosthesis measure the contact and pressure applied to an object while holding it. This information is transmitted to the nerves of the patients that lead to their brains. In this way, patients can feel when they touch an object, its characteristics and how hard they press it, which is crucial to imitate a biological hand.
The ghost effect
People who lose an arm or a leg often experience ‘phantom’ sensations, as if the missing part of the body remains, even if not physically present. When force sensors on the prosthetic thumb react, the researcher notes, patients “feel” that the sensation comes from their ghost hand. Precisely in which part of the phantom hand varies between patients, depending on which nerves in the stump receive the signals. The lowest level of pressure can be compared to touching the skin with the tip of a pencil. As the pressure increases, the sensation becomes stronger and more and more “electric.”
The implementation of this new technology took place in the Sahlgrenska University Hospital. More than a million people worldwide suffer from limb loss and the ultimate goal of the research team, in collaboration with Integrum AB, is to develop a widely available product suitable for as many people as possible.
“Right now, patients in Sweden are participating in the clinical validation of this new prosthetic technology for arm amputation,” says Ortiz. We hope that this system will be available outside of Sweden in a couple of years, and we are also making considerable progress with similar technology for leg prostheses, which we plan to implant in a first patient later this year. ”