Our rapidly developing ability to interface neurons and electronics offers amputees much more functional prostheses (though it is still a long and winding road). Here are some encouraging recent developments:

● A newer technology pioneered at Helsinki University Hospital and Imperial College London enables improved compatibility between a prosthesis and the remaining portion of the amputee’s limb. One current problem is that the connections between the prosthesis and the muscle that gives the commands (the myoelectric interface) can grow weaker due to external factors like sweating.

Currently existing systems require adjustments or other measures from the user, but Yeung and his team developed a fully automated system that learns during normal use and thus adapts to varying conditions.

“In this system, the user and the system learn from each other simultaneously. This has potential benefits in improving the convenience and robustness of robotic prostheses,” Yeung says.

Aalto University, “A new type of hand prosthesis learns from the user, and the user learns from the prosthesis” at Medical XPress (March 18, 2022) The paper is open access.

● There’s new research interest in the four in every ten thousand babies who are born missing a limb. Would they be best off to adjust to a prosthesis as early as possible? Not much information is available but now Limbitless Solutions at Wolfson Children’s Hospital of Jacksonville, Florida, is looking at how the brain responds:

The four-month clinical trial will examine if Limbitless’ prosthetic — paired with its custom training video game — will impact the motor control center of the brain. Researchers will closely monitor any changes in the signals the brain sends to the muscle groups that direct the bionics’ movement.

They will do this using advanced functional magnetic resonance imaging (MRI) techniques before and after prosthetic use and training. Additionally, researchers will use a method known as tractography — where MRI scans visualize the nerve pathways — to identify new or more robust pathways resulting from the training.

The study is unique because it combines advanced imaging techniques with novel prosthetics and video-game-based training to evaluate motor cortex engagement.

Wolfson Children’s Hospital, “New clinical research will test brain’s ability to adapt to advanced bionic limbs” at Fernandina Observer (March 19, 2022)

● Another recent development is prosthetic software that can distinguish a user’s intention by the way muscles move, but that requires decoding the signals the brain is sending through the nerves:

The problem is that users usually have to contract their muscles in specific combinations of patterns to generate hand or wrist motions. These patterns are often counterintuitive, time consuming and frustrating…

What’s needed is a way to measure and decode nerve signals so that they can be used to intuitively control prosthetic arm, hand and finger movement.

Now Diu Khue Luu and Anh Tuan Nguyen from the University of Minnesota with colleagues, have found a way to do this using an AI decoder that learns the user’s intention based on the nerve signals it senses in the arm. “We present a neuroprosthetic system to demonstrate that principle by employing an artificial intelligence (AI) agent to translate the amputee’s movement intent,” they say.

The Physics arXiv Blog, “AI Is Revolutionizing Prosthetic Arm Control” at Discover Magazine (March 21, 2022) The paper is open access.

It’s still a long road but we’ve certainly made some refinements since the first known prosthesis, as noted by Samanth Subramanian:

… the earliest true prosthetic we know was this wooden big toe… It dates to around 1000 BC, it was found attached to the right foot of a mummified Egyptian woman who’d lost that big toe. And we don’t know why she had it. One theory is that she had gangrene and it had to be amputated. But the big toe is so crucial to how we walk and maintain balance, that there was a need for a prosthetic and this must have been remarkably effective. So was essentially just tied on to the remainder of the foot. And she would have sort of walked on that until the day she died.

Kira Bindrim, “Modern prosthetics go beyond bionic limbs—and into the brain” at Quartz/MSN (March 15, 2022)

The wood and leather device from ancient Egypt is pictured here.

Will prosthetics become so good that some people will prefer them to natural limbs? The controversy over South African runner Oscar Pistorius, who competed at the 2012 Olympics on prosthetic legs, has raised the question:

Runners who’ve faced off against Oscar Pistorius say they know when the South African is closing in on them from behind. They hear a distinctive clicking noise growing louder, like a pair of scissors slicing through the air—the sound of Pistorius’s Flex-Foot Cheetah prosthetic legs.

It’s those long, J-shaped, carbon-fiber lower legs—and the world-class race times that come with them—that have some people asking an unpopular question: Does Pistorius, the man who has overcome so much to be the first double amputee to run at an Olympic level, have an unfair advantage? Scientists are becoming entwined in a debate over whether Pistorius should be allowed to compete in the 2012 London Games.

Rose Eveleth, “Should Oscar Pistorius’s Prosthetic Legs Disqualify Him from the Olympics?” at Scientific American (July 24, 2012)

That debate turned out to be long, complex, and technical. It will likely be resolved by the development of newer technologies, some of which will be better than natural limbs for certain purposes — in the same way that Watson could triumph at Jeopardy but flop in medicine.

The issues around Pistorius’s own career were overshadowed by his conviction for murder in South Africa but the question is bound to come up for other amputees. Also, what about electronic enhancements of natural limbs? How much is too much to be fair in sports? And at what point will some desperate seekers of Olympic glory want replacement of healthy natural limbs, not just enhancement?

Today it is mostly an academic bioethics debate. We are still at the point where most of the world’s amputees don’t have anything like affordable state-of-the-art prosthetics. But even in the process of tackling that problem, we inevitably create new issues that can take us into uncharted territory.

You may also wish to read:

A Lego toy that solves mazes may bring new hope to amputees. Organic materials that enable computer chips to work like neurons could improve the usability of prostheses. A quarter century ago, CalTech engineering prof Carver Mead saw that electronic systems would work better for us if they imitated such natural nervous systems.

The Bionic Man was science fiction; the bionic hand is not. A recent internet-savvy bionic hand, developed by an American neuroscientist and computer engineer, is the most flexible yet, with sensory feedback. The trouble is, if the new bionic hands are going to help most of the world’s amputees , they can’t cost six million dollars, as in the old TV show.

Prosthetic hand controlled by thoughts alone? It’s here. Decades ago, no one could control a prosthesis only by thought. There is lots of room for the field to grow still. (2020)

New mind-controlled robot arm needs no brain implant. The thought-controlled device could help people with movement disorders control devices without the costs and risks of surgery. (2019)

High tech can help the blind see and amputees feel. It’s not a miracle; the human nervous system can work with electronic information. (2019)