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A bionic leg driven by the body’s nervous system restores a natural walking gait much more effectively than other prosthetic limbs, a clinical trial led by Massachusetts Institute of Technology has shown.
The technique, unveiled in the journal Nature Medicine, is the latest advance in neurotechnology. The fast-moving field promises huge benefits for people with disabilities, including brain-computer interfaces that help to restore movement in patients with spinal cord injuries.
The MIT team developed a surgical procedure to reconnect severed muscles and nerves, which then generate electrical signals. These are detected by electrodes placed on the skin and used to control a prosthetic leg.
The technology significantly improved patients’ walking speeds, as well as their ability to climb stairs and avoid obstacles, the research team said in the study, published on Monday.
Hugh Herr, the project leader, called the trial “the first in history that shows a leg prosthesis under full neural modulation . . . No one has been able to show this level of brain control that produces a natural gait, where the human nervous system is controlling the movement, [rather than] a robotic control algorithm.”
The surgery, known as agonist-antagonist myoneural interface (AMI), reconnects muscle fibres left behind in the remaining tissue, which work together in an intact limb but are severed after a standard amputation.
Restoration of dynamic interaction between muscles gives amputees back some proprioception — the ability to sense the position and movement of limbs — in the prosthetic leg. When they think about moving the missing parts of their lower leg, such as calf and ankle, skin-mounted electrodes transmit the neural signals to electronic receivers on their prosthetic limb, which moves accordingly.
“What happens is almost miraculous,” said Herr, whose own lower legs were amputated in 1982 when he suffered severe frostbite after a mountaineering accident. “Patients can walk at normal speeds almost without thinking about it.”
The clinical trial featured 14 participants with below-the-knee amputations in one leg — seven underwent AMI while the others formed a control group that had conventional surgery. All were fitted with high-tech prosthetic limbs with powered ankle and movement sensors.
The AMI group could on average walk 41 per cent faster than the controls, matching the speed of people without amputations and navigating much more easily around obstacles and on stairs.
The procedure may give the best results when carried out at the same time as an amputation, but AMI also worked well in patients who had lost their limbs a long time ago, the researchers said.
Herr believes he has sufficient traces of muscle left to benefit from the procedure more than 40 years after his amputations.
“I am thinking of doing it with both my legs,” he said.
MIT has patented the AMI technology and Herr aims to have commercial versions of the product available in about five years.
He said the broader aim of his lab was “rebuilding human bodies” with components that people could control themselves rather than relying on ever more sophisticated robotic devices that did not feel like part of their own bodies.
Herr added: “The approach we’re taking is trying to comprehensively connect the brain of the human to the electro-mechanics.”