Foot prostheses that give feedback

Tiredness, unsteadiness or even phantom pain: leg prostheses help people back into everyday life after an amputation, but can also cause problems. There is a simple reason for this: ordinary prostheses do not transmit neuronal signals to the patient’s brain. So they do not receive any information about movements or contact with the ground. Now, an international research team comprising Freiburg microsystems engineer Prof. Dr. Thomas Stieglitz and headed by  Prof. Dr. Stanisa Raspopovic, Professor of Neuroengineering at ETH Zürich, has studied this challenge in relation to neuroprosthetics. To do this, they implanted electrodes in the thighs of amputees, so as to stimulate the nerves and thus produce communications between the brain, the leg and the prosthesis. The scientists have published their results in the journal Nature Medicine.

The researchers studied two people whose legs were amputated above the knee. They implanted four electrodes each in the tibial nerve. The nerve was stimulated to deliver signals about knee movement and ground contact of the sole of the foot derived from technical sensors like a sensorized shoe sole. The subjects were able to increase the speed at which they walked, and felt more confident; their emotional and physical tiredness was reduced, and they had fewer phantom pains.

This latest study follows on from a discovery from 2012: at that time, Stieglitz’s team introduced electrodes that helped provide amputees with a sensitive replacement hand. Combined with the LifeHand 2 prosthesis, the electrodes gave the patients an artificial sense of touch and enabled them to control the movements of the hand. Until now, all fundamental research that has taken place around the world has used implanted electrodes, where the cables are passed out through the skin. The next step is a completely implantable system. Then the scientists will be able to conduct large-scale studies on the clinical benefits of neuroprostheses that can recreate sensory feedback. Later they hope to bring the product onto the market once it has been fully-developed and licensed. Realistically, this will take up to ten years because of the regulations concerning medical devices in Europe, however these results are already seen as promising.

Original publication:

Francesco Maria Petrini, Marko Bumbasirevic, Giacomo Valle, Vladimir Ilic, Pavle Mijović, Paul Čvančara, Federica Barberi, Natalija Katic, Dario Bortolotti, David Andreu, Knut Lechler, Aleksandar Lesic, Sanja Mazic, Bogdan Mijović, David Guiraud, Thomas Stieglitz, Ásgeir Alexandersson, Silvestro Micera, Stanisa Raspopovic (2019): Sensory feedback restoration in leg amputees improves walking speed, metabolic cost and phantom pain. In: Nature Medicine.

Watch a video on Thomas Stieglitz’s research into prostheses