An international team of researchers, led by the ETU Zurich and Lausanne-based start-up company SensArs, have developed an interface to connect a leg prosthesis with the residual nerves present in the user’s thigh, thus providing sensory feedback. The sensors gave prosthetic leg wearers a sensation of flexing and landing their legs, giving them the ability to walk more quickly and confidently.
In the study conducted in collaboration with the University of Belgrade, the scientists tested this neurofeedback system with two volunteers who have an above-knee leg amputation and use a leg prosthesis.
The solution benefited the amputees in various ways, as the researchers reported in the latest issue of the journal Nature Medicine. “This proof-of-concept study shows how beneficial it is to the health of leg amputees to have a prosthesis that works with neural implants to restore sensory feedback,” said Stanisa Raspopovic, a Professor at the Institute of Robotics and Intelligent Systems at ETH Zurich.
To provide the nervous system with sensory information, the scientists attached tactile sensors to the sole of the prosthetic foot, and collected the data on knee movement provided by the prosthesis’s electronic knee joint.
For the three-month trial, surgeons placed tiny electrodes in each volunteer’s thigh and connected them to the residual leg nerves.
“The goal of the surgery was to introduce electrodes in the right places inside the nerve to allow the restoration of lifelike sensory feedback, and to allow the stability of the electrodes,” said Marko Bumbasirevic, Professor and orthopedic microsurgeon at the Clinical Centre of Serbia in Belgrade, the clinician responsible for the electrode implant. The electrodes were developed by scientists from the University of Freiburg, and the prosthesis came from the prosthetic company Össur; both were actively involved in the project.
The researchers developed algorithms to translate sensor information into impulses of current, which were delivered to the residual nerve. The signals from the residual nerves are conveyed to the person’s brain, which is thus able to sense the prosthesis and helps the user to adjust their gait accordingly.
The two men in the trial then went through a series of tests, alternating trials with or without neural feedback. When connected, the men had a much easier time walking and breathed more naturally. For the first month they tested the best way to stimulate their nerves to generate the most realistic sensations. “They described it as close to lifelike,” said Raspopovic.
Subsequent trials outdoors found the men being able to walk faster and with greater confidence in their limbs.
Also, the volunteers significantly reduced their incidence of phantom limb pain. One man’s phantom limb pain went away completely, and the other’s fell substantially.