Amputees can regain a normal gait with the use of “smart” prosthetic legs; however, this is achieved via robotic sensors and algorithms that propel the limb forward at preset speeds.
Giving patients complete neurological system control over the limb would be a better approach, and an MIT research team claims to have achieved precisely that.
Researchers claim in the July 1 issue of the journal Nature Medicine that a fully normal walking gait, powered entirely by an individual’s neurological system, can be restored using an experimental surgical method paired with a state-of-the-art robotic limb.
According to researchers, the process re-connects muscles in the residual limb, giving patients precise, instantaneous feedback on the posture of their prosthetic limb during gait.
Seven patients who underwent this operation were able to walk more quickly, avoid obstacles, and climb stairs with considerably greater ease than those who had a standard amputation.
Hugh Herr, a senior researcher and co-director of MIT’s K. Lisa Yang Center for Bionics, stated, “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, not a robotic control algorithm.”
According to background notes from researchers, pairs of muscles alternately contract and extend control of most arm and leg movements.
The interaction of these paired muscles is disrupted in a typical below-the-knee amputation, which makes it challenging for the nervous system to follow and govern movement.
People with this form of amputation thus have difficulty controlling a prosthetic limb since they are unable to perceive the leg’s location in space precisely. To develop a walking stride and adapt to slopes and obstacles, they are dependent on robotic controllers and sensors.
Herr and colleagues developed agonist-antagonist myoneural interface (AMI) surgery to assist individuals in gaining complete neurological control over their prosthetic legs.
During AMI surgery, the two ends of the muscles are connected as opposed to just cutting off muscle pairs. In doing so, they are able to maintain dynamic communication inside what is left of the leg.
According to researchers, AMI surgery can be performed either at the original amputation or as a follow-up procedure.
According to a 2021 investigation conducted by Herr’s lab, the muscles of a leg that had undergone AMI surgery created electrical signals resembling those of an intact limb.
Subsequently, the researchers set out to determine how those electrical signals could be used to both command a prosthetic limb and obtain input from the limb regarding its position when walking.
In this manner, an amputee from an AMI procedure might operate a prosthetic leg and utilize the input to modify their stride when necessary autonomously.
The latest research demonstrates that sensory feedback does, in fact, result in a seamless, almost natural capacity to walk and negotiate obstacles.
Seven AMI amputees and seven patients who underwent conventional below-the-knee amputations were compared in the study.
Every participant used the same kind of bionic leg, a motorized ankle prosthesis with electrodes that can pick up electrical impulses from the leg’s main muscle groups.
These signals are sent to a robotic controller, which aids in the prosthesis’s computation of the ankle’s bending, torque application, and power delivery.
The amputees were assessed on their ability to walk on level ground, up a hill, down a ramp, up and down stairs, and cruise around a level area without running into anything.
