The newly developed bionic knee can help people with over-knee amputations walk and climb more easily than traditional prosthetics can.
The new prosthesis, described in Journal Science on July 10, connects to the user’s legs via a titanium rod attached to the femur and an electrode permanently implanted into the leg muscles. In addition to improving athletic ability, prostheses helped users feel a greater sense of ownership and agency than prosthetic limbs, the researchers said.
“The tissue-integrated prosthesis – fixed to the bone and directly controlled by the nervous system – is not merely a separate, lifeless device, but a system carefully integrated into human physiology,” in the statement. “It’s not just a tool that humans employ, but rather an integral part of the self.”
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Traditional prosthetic legs adhere to the user’s residual limbs with sockets, but new bionic prostheses interface directly with muscles and bones. In doing so, we can utilize the surgical approach to amputation that was recently developed by Herr and colleagues. In this new approach, the surgeon reconnects pairs of muscles that stretch and contract against each other, such as residual hamstrings and quadriceps, which stretch and contract against each other, allowing them to communicate with each other. Traditional knee amputations make controlling the prosthesis more difficult because these muscles are not reconnected.
The new study also introduced a technique to integrate the system into the residual femur at the site of cutting. This technique provides greater stability and load bearing than traditional prostheses.
“All parts work together to get information in and out of the body and mechanically get better interfaces with the devices,” said Tony Shu, a biomechatronics researcher who conducted the research during MIT graduate students, in a statement. “We don’t use sockets, but instead load skeletons directly, which are part of the body that is supposed to load. This can be uncomfortable and frequently lead to skin infections.”
In a new study, two previously undergone conventional knee amputations have undergone surgery to receive both muscle connection procedures and osteointegration implants. In this study, these people were compared to eight people who had muscle surgery but had neither bone implants, and had either. All study participants used the same driven knee prosthesis, although connected in a variety of ways to tasks such as climbing stairs, stepping on obstacles, and correcting bionic knees.
Those who received the combined system performed better on almost all tasks than those who only had surgery to connect to the muscle, the team found. They also performed much better than those who used traditional prosthetics.
Additionally, two participants who underwent both muscle surgery and implants showed a greater increase in the meaning of ownership, or the ability to intentionally control the device after completing the agency or study task.
“No matter how sophisticated a robotic prosthesis AI system is, it will feel like a tool to the user, just like an external device,” Herr says. “But this organizationally integrated approach means that when you ask a human user what their body is, the more they integrate it, the more prosthetics are actually part of the self.”
Prosthetics are not available commercially yet. Herr said in a statement that clinical trials for Food and Drug Administration approval could take around five years.
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