The Next Step in Prosthetics

Assistive technologies have come a long way in recent years, offering individuals with a variety of disabilities previously unattainable levels of independence and an improved quality of life. Technologies that assist with mobility impairments, in particular, have rapidly increased in sophistication. Gone are the days when basic wheelchairs and crutches were the only options. Today, advanced mobility aids such as powered exoskeletons, smart wheelchairs, and custom prosthetics are transforming lives. These innovations enable individuals to navigate complex environments, engage in physical activities, and perform tasks that were once out of reach.

The integration of artificial intelligence into these devices has further enhanced their functionality. Consider prosthetic legs, for example. Intelligent algorithms have been used to provide real-time adjustments and personalized support that makes walking seem much more natural. However, there is still a lot of work yet to be done. As it presently stands, these systems rely on controllers that run predefined algorithms that are not ideal for every individual and situation. Accordingly, they can be a bit awkward to use at times.

The dream has long been to fully integrate prosthetic limbs with the user’s nervous system to give them total and natural control over them. We may not be all the way there just yet, but the work of a team led by researchers at MIT has brought us much closer. They have developed a neuroprosthetic interface and surgical procedure that ties a prosthetic leg directly into the wearer’s nervous system. It was demonstrated that this technique enabled users to walk much more naturally, and also gave them a greater ability to avoid obstacles and climb stairs than if they were using a traditional prosthetic leg.

Under normal walking conditions, our brains receive feedback from pairs of muscles that are in push-pull relationships. This feedback gives us a sense of where our legs are positioned in three-dimensional space. Without this feedback, which is not present after most amputations, normal walking becomes very difficult. To overcome this problem, the team utilized an approach in which pairs of muscles are attached to each other, rather than being severed, as would typically be done in an amputation. This allows for the normal feedback signals to be produced in the residual limb.

Of course the limb is still missing, so those phantom signals are of little use. For this reason, the researchers designed a neuroprosthetic interface that can be implanted into the remaining portion of the limb to tap into the electrical signals generated by the muscles. This information was then fed into a prosthetic leg to control it. The result is that the user of the system feels normal feedback while walking, and the artificial limb reacts to their intentions as if it were a natural limb.

A study was conducted to assess how well the team’s approach worked under real-world conditions. Seven individuals that had the new surgery were outfitted with a prosthetic leg, while seven others that did not have the surgery were given the same type of prosthetic leg. They were then asked to walk, climb stairs, avoid obstacles, and several other common tasks. The results showed that those that had had the surgery could walk faster and more naturally, and also that they had better coordination.

Interestingly, these positive results were achieved despite the fact that the individuals who have the surgery only receive about 20 percent of the sensory feedback that those without an amputation would receive. This hints at the possibility of further improving the system in the future via better surgical techniques.