Autonomy at your fingertips

Christine Azevedo and her colleagues at Inria have worked miracles to restore functional use of the hands and wrists of people with tetraplegia.¹ have achieved thanks to selective neural electrostimulation. When science advances with its hand on its heart.

It's been over two years since Maxime last held a glass of beer in one hand or reeled in his fishing rod. Soon, he'll be eagerly turning the pages of his novel, and will be able to use the catheter he uses to evacuate his urine. For Maxime is quadriplegic. For a few weeks now, he has been taking part in the neural electrostimulation trial led by researcher Christine Azevedo, head of the Camin team, and is rediscovering with them gestures that have become impossible since his accident.

Thanks to orthopedic surgeon Jacques Teissier's team at Montpellier's Clinique Saint Jean, scientists implanted two small electrodes wrapped around his nerves in his arm. These are epi-neural electrodes," explains the researcher. They will send electrical stimulation to the nerves, which will then activate the muscles of the hand and wrist to generate movement." The process may look simple, but it's the fruit of ten years' research.

Left behind

It all began when the American company that developed the Freehand system in the 2000s decided to cease trading. " The system consisted of implanting electrodes in the forearm muscles, connected to an implant that enabled the hand to be opened and closed by moving the shoulder, for example", explains the researcher. From one day to the next, the 250 tetraplegic patients fitted with the implant find themselves left out in the cold. Some of them had been operated on by Jacques Teissier and are being monitored by Charles Fattal, head physician at the Bouffard-Vercelli functional rehabilitation center in Perpignan. Together with Christine Azevedo and two Inria researchers, David Andreu and David Guiraud, they form the quintet behind a new neural electrostimulation method.

"One of the shortcomings of the Freehand system was to implant an electrode in each of the eight muscles of the forearm. We wanted something less invasive," she recalls. As part of the team, David Guiraud had already worked on neural stimulation to restore walking in paraplegics" ( read : A giant step forward for prostheses). Adapted to the upper limbs, this technique can activate all forearm muscles by implanting just two electrodes: one on the radial nerve and the other on the median. Problem: since these nerves control all the muscles, how do you specify the stimulation to generate only the chosen movement?

28 days...

"The challenge was to activate sub-sections of the nerve to obtain useful gestures," confirms Christine Azevedo. The special feature of the epi-neural electrodes manufactured by the German company Cortec is that they wrap around the nerve to provide various points of contact. After an initial phase of successful experimentation on rabbits, nine orthopedic surgery patients agreed to let the team take advantage of their arm surgery to implant the electrodes, test them and remove them before they woke up. "We saw that activating different contacts around the nerve generated very specific movements: closing all the fingers, extending the wrist..."

It's 2020, and the Camin team and its partners are preparing phase 3 of the project, which will be called Agilis and then Agilstim: implanting neural electrodes in four patients for 28 days. In the meantime, the covid exploded and only two patients took part in the trial, with two more to follow in 2023. To enable them to trigger the movement themselves, the electrodes are connected by two cables to a stimulator located outside their body. "Patients control it using different types of commands: buttons they press with their elbow or head, a sensor located on the shoulder which transforms movements or muscle contraction into a signal, a voice command..."

On the fingers of one hand

For 28 days, researchers and patients meet three or four times a week to test the device. First, the stimulator must be set up to observe which muscles are activated by each of the electrode's contact points, as the configuration of the nerves differs from one patient to another. Then come the sessions aimed at producing specific movements: five imposed tasks and five tasks chosen by the patients themselves. "The first wanted to brush his teeth on his own and, above all, operate a door handle because he'd been stuck before. Another wanted to be able to sign documents or plug in a USB stick. Not everyone puts the same meaning into these gestures, but what's at stake is a form of autonomy. And they all succeeded! "These are very powerful moments. Scientifically, we enjoy ourselves, but at the heart of it all is the human element," Christine Azevedo emphasizes.

By 2025, four new patients will be implanted. Montpellier-based start-up Neurinnov, launched in 2018 by David Andreu and David Guiraud to enhance and bring to fruition their research into selective neural stimulation, is working on the development of an implantable stimulator in patients' bodies this time. In 2026, new trials will be carried out to validate this implant and move towards CE marking and market launch. For Maxime, the 28 days have now passed and the electrodes have been removed from his arm, but he knows that the years separating him from permanent implantation of this device can now be counted on the fingers of one hand.

1. *Lirmm (UM, CNRS, Inria, UPVD, UPVM)
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