Scientists have bridged the gap between prosthetics and the human body, allowing users’ nervous and skeletal systems to control their replacement limbs. The breakthrough, which has stood up to years of daily use, has restored around 80% of daily hand and finger movement to a Swedish amputee and may have even relieved the phantom pain she’s experienced since her accident nearly 20 years ago.
The team led by Max Ortiz Catalan, a neuromusculoskeletal engineer and head of neural prosthetics research at Australia’s Bionics Institute, has published the results in Science Translational Medicine. The study describes how a man with an above-elbow amputation can use his thoughts to control every finger of a robotic arm attached to his remaining upper limb. The researchers used a “targeted muscle reinnervation” technique to obtain more electrical signals from the muscles to prompt the robotic limb’s movements. They also used a titanium fixture that they anchored into the remaining bone, making it more comfortable than socket attachments commonly worn.
Previously, other prosthetics have picked up muscle signals by running electrodes on or within the skin, which is not practical for daily use. But to make their system work, the researchers dissected the bundle of nerve fibers that carry signals from the brain to the muscles of the upper arm. They then rerouted some nerve fibers to new muscle targets in the arm, including muscle tissue grafted from the leg. They also anchored electrodes to the bones of the arm and wrist and wired these up to the robotic arm. A processor inside the prosthetic then translates the muscle signals into movement commands for the robotic arm and fingers.
When the arm moves, the robot sends a signal to the nerves and skeleton in the remaining part of the arm, stimulating the muscles and skin of the remaining limb to generate the sensation of touch. The process is called teleoperation. The system also includes another feature designed to address phantom pain. When the patient’s bionic limb touches her remaining hand or elbow, the system will generate a corresponding stimulus to prevent phantom pain and restore the sense of “proprioception” that a normal limb provides.
This approach to skeletal integration, developed by the Italian prosthetics company Prensilia, is a significant leap over traditional socket attachments that are only anchored to the socket of the missing limb. It eliminates the need for a prosthetic socket, which can lead to discomfort and problems with attachment and removal. This system is a prototype, and the researchers hope to develop a more durable version for commercial use. Other researchers are also working on intuitive, intelligent prosthetic limbs that can tap into the brain or nerves to let an amputee think about moving their fingers and see those movements executed by their robotic arm. But it will be a while before such systems are ready for widespread use and even longer before they reach the level of performance that could help many users.
