Cutting-edge prosthetic technology helps amputees achieve a more natural walking pattern, but falls short in allowing users full control over their prosthetic limb via their nerves. Instead, they rely on robotic sensors and controllers programmed with predefined walking algorithms.
Introducing a Groundbreaking Solution
The latest surgical approach and neuroprosthetic interface devised by researchers at MIT and Brigham and Women’s Hospital have successfully enabled individuals with below-knee amputations to walk in a more natural manner. Through this innovative surgical procedure, which reconnects muscles in the residual limb, patients can now receive crucial “proprioceptive” feedback regarding their prosthetic limb’s position in space.
Improving Mobility and Comfort
Seven patients who underwent this surgery demonstrated enhanced walking speed, improved obstacle avoidance, and more natural stair-climbing abilities compared to those with conventional amputations.
“This groundbreaking study is the first to exhibit a leg prosthesis that operates under full neural modulation, resulting in the emergence of a biomimetic gait. This level of brain control, where the human nervous system directs movement rather than a robotic algorithm, has never been achieved before,” explained Hugh Herr, a leading expert in bionics at MIT.
Moreover, individuals experienced reduced discomfort and muscle wastage following the agonist-antagonist myoneural interface (AMI) surgery, which has benefited around 60 patients worldwide, including those with arm amputations.
Lead author Hyungeun Song from MIT’s Media Lab highlighted the study’s publication in Nature Medicine.
Enhanced Sensory Feedback
During a standard below-knee amputation, the interaction between paired muscles responsible for limb movements is disrupted. This impedes the nervous system from accurately detecting muscle position and contraction rate, crucial for efficient limb control.
Individuals with such amputations often struggle to control their artificial limb due to an inability to precisely sense its location. Consequently, they heavily rely on robotic limb controllers integrated into the prosthesis.
In an effort to enable a natural gait driven by the nervous system, Herr and his team developed the AMI surgery. This method preserves the natural muscle interactions by linking muscle ends, allowing dynamic communication within the residual limb. The procedure could be performed during the initial amputation or as a subsequent revision.
“Through the AMI amputation technique, we aim to establish physiological connections between native agonist and antagonist muscles. This enhances the user’s phantom limb mobility with natural proprioception and range of motion,” Herr elaborated.
Transformative Results
In a recent study, patients who underwent the AMI surgery exhibited more precise control over their amputated limb muscles, producing signals akin to those of their intact limb.
Expanding on these findings, researchers explored whether these electrical signals could command a prosthetic limb while providing position feedback. This sensory input empowered wearers to adjust their gait voluntarily, culminating in a smooth and near-natural walking experience, as observed in the recent Nature Medicine publication.
Restoring Mobility and Confidence
Individuals with the AMI neuroprosthetic interface surpassed their traditionally amputated counterparts in various tasks, showcasing improved walking speed, obstacle negotiation, and natural movement coordination between prosthetic and intact limbs.
Notably, these natural behaviors emerged despite the AMI’s sensory feedback being less than 20% of what an individual without an amputation would typically receive.
“Our research highlights the remarkable potential of even a marginal increase in neural feedback from the amputated limb to significantly enhance bionic neural control. This allows direct neural regulation of walking speed, terrain adaptation, and obstacle avoidance,” emphasized Song.
This collaborative effort signifies a noteworthy stride in restoring function for severe limb injury patients, shaping the future of patient care, according to Matthew Carty, a co-author and surgeon at Brigham and Women’s Hospital and Harvard Medical School.
Empowering User Control
Achieving neural control through the user’s limb marks a vital step toward Herr’s objective of reconstructing human bodies, aiming to bridge the gap between sophisticated robotic controllers and the user’s sensory connection to the limb.
“Our approach focuses on establishing a comprehensive connection between the user’s brain and the limb’s electromechanics, fostering a sense of embodiment with the prosthesis and enhancing overall functionality,” Herr noted.
The study received support from the MIT K. Lisa Yang Center for Bionics, the National Institute of Neurological Disorders and Stroke, the Neurosurgery Research Education Foundation Medical Research Fellowship, and the Eunice Kennedy Shriver National Institute of Child Health and Human Development.
