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A pioneering surgical procedure provides amputees with bionic limbs that are controlled directly by the nervous system, enabling patients to sense the limb’s position in space.
Scientists demonstrated the success of the technique in a new study of seven people who received bionic legs, which was published Monday (July 1) in the journal Nature Medicine. Including these seven, about 60 people worldwide have undergone this type of procedure, which can be used to install either bionic legs or arms.
“This is the first prosthetic study in history to show a prosthetic leg under full neural modulation, exhibiting a biomimetic gait.” Hugh Herrco-author of the study and a professor of media arts and sciences at MIT, said in a STATEMENT. In other words, the synthetic prosthesis is able to supplement the lost function of the missing limb and thereby produce a natural gait.
“No one has been able to show this level of brain control that produces a natural gait, where the human nervous system controls the movement, not a robotic control algorithm,” Herr said.
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The operation itself, known as agonist-antagonist myoneural interface (AMI), involves reattaching the muscles in the patient’s remaining limb after a below-knee amputation, in the case where the patient is receiving a bionic leg.
Electrical signals from central nervous system, which transmit instructions for movement, can then pass between these muscles and be detected by electrodes in a newly installed prosthetic limb. Signals are received by a robotic controller in the prosthesis that enables it to control the patient’s gait or gait. Signals about the position and movement of the patient’s prosthesis are then fed back to the nervous system.
In a series of experiments described in the new paper, seven patients who underwent AMI surgery were able to walk faster than people who received the same type of prosthetic limb but who had traditional amputations. Some of the patients could even walk at the same pace as people without amputation. They could also avoid obstacles and climb stairs more naturally than patients who underwent traditional amputations.
Current technology for prosthetic limbs already enables amputees to achieve a natural walking gait, according to the team that performed the surgery. However, these prosthetic limbs rely on robotic sensors and controllers to actually move in a predetermined algorithmic pattern, the team said. AMI, in contrast, enables limbs to respond dynamically to signals from the body.
“The approach we’re taking is trying to fully connect the human brain with electromechanics,” Herr said.
Patients who underwent AMI also experienced less pain and muscle atrophy, the scientists reported.
AMI can also be used for people who have an arm amputation, the team said, and the surgery can be done either during the patient’s original amputation or at a later date.
“This work represents another step in demonstrating what is possible in terms of restoring function in patients suffering from severe limb damage.” Dr. Matthew Cartyco-author of the study and an associate professor of surgery at Harvard Medical School, said in the statement.
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