Prosthetic limb controlled by thought

The act of walking may not seem like a feat of agility, balance, strength and brainpower. But lose a leg, as Zac Vawter of Washington state did after a motorcycle accident in 2009, and you will appreciate the myriad calculations that go into putting one foot in front of the other.

Taking on the challenge, a team of software and biomedical engineers, neuroscientists, surgeons and prosthetists has designed a prosthetic limb that can reproduce a full repertoire of ambulatory tricks by communicating with Vawter's brain.

A report published on Wednesday in the New England Journal of Medicine describes how the team fit Vawter with a prosthetic leg that has learned - with the help of a computer and some electrodes - to read his intentions from a bundle of nerves that end above his missing knee.

For those who have lost a leg or part of one due to injury or disease, Vawter and his robotic leg offer the hope that future prosthetics might return the feel of a natural gait, kicking a soccer ball or climbing into a car without hoisting an inert artificial limb into the vehicle.

Vawter's prosthetic is a marvel of 21st-century engineering. But it is Vawter's ability to control the prosthetic with his thoughts that makes the latest case remarkable. If he wants his artificial toes to curl toward him or his artificial ankle to shift so he can walk down a ramp, all he has to do is imagine such movements.

The work was done at the Rehabilitation Institute of Chicago under a US$8 million grant from the US Army.

"We want to restore full capabilities" to people who have lost a lower limb, said Levi Hargrove, lead author of the new report.