Zac Vawter controls bionic leg with his thoughts By Tom Leonard In New York In a major medical breakthrough, American doctors have developed a bionic leg that is controlled by its wearer's thoughts. Zac Vawter lost his right leg in a motorcycle accident but now he just has to think and his artificial limb will rotate, walk or even climb stairs. Mr Vawter, a software engineer from Seattle, lost his leg just above the knee four years ago and has since become the test pilot for pioneering technology which could transform life for thousands of amputees. Mind control: Zac Vawter has been given a new type of bionic leg that reacts based on brainwaves meaning that he controls his foot with his thoughts Moving on: Vawter, a software engineer from Seattle, lost his leg just above the knee four years ago in a motorcycle accident The bionic leg works by harnessing nerves that formerly regulated the limb's movement. When Mr Vawter thinks he wants to move his leg, the brain signal travels down his spinal cord and is picked up by electrodes in the bionic limb. Two of the severed nerves in his leg were "rewired" into his hamstring, the muscle at the back of his leg. They in turn communicate with sensors inside the prosthetic leg socket which send a message to a computer. The computer can then work out how the patient is intending to move and help him. Mr Vawter can bend his knee, extend his leg, rotate his ankle and walk normally. Unlike existing robotic legs, the bionic one allows a normal, smooth gait no matter what the incline. Totally new: When Mr Vawter thinks he wants to move his leg, the brain signal travels down his spinal cord and is picked up by electrodes in the bionic limb Independence: The bionic leg works by harnessing nerves that formerly regulated the limb¿s movement The biggest improvement over standard prosthetic legs is when he climbs stairs, he says. Ordinary artificial legs have to be pulled along after the healthy leg takes each step. But the thought-controlled leg he can walk foot-over-foot so that - apart from the whirr of the motor - anyone watching wouldn't know he was wearing a prosthesis. "It makes a phenomenal difference," said Mr Vawter, who only wears the bionic leg occasionally as it is a prototype. He accepts there are some things he still can't do that he once enjoyed, such as running and jumping up to shoot a ball through a basketball hoop.Its developers say they now need to make the bionic limb lighter and less noisy. Range of movement: Vawter can bend his knee, extend his leg, rotate his ankle and walk normally Scientists have already developed a thought-controlled bionic arm but a leg was far more challenging as the small motors must be powerful enough to allow someone to stand up and propel themselves forward. The study by the Rehabilitation Institute of Chicago was funded by the US Army but its leader, Levi Hargrove, said benefits could go far beyond amputees. He wants to restore "full ability" to all patients, not just otherwise able-bodied war veterans. For the elderly, "this could mean the difference between living in their home longer and having to go to a nursing home," he said. Its eventual cost has yet to be determined but the Chicago team say a version of their leg could be available to more than a million American amputees within three to five years.