Name: The Evolution of Prosthetic Leg Technology
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Typical amputation processes don't take into account our ability to sense the world around us. Now, a team of researchers and doctors is working to address this problem.

Amputation procedures haven't changed much since the Civil War era.

The Evolution of Prosthetic Leg Technology

Evolution of Prosthetic Leg Technology

Koch Foundation

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Typical amputation processes don't take into account our ability to sense the world around us. Now, a team of researchers and doctors is working to address this problem.

Amputation procedures haven't changed much since the Civil War era.

Tech & Engineering

The Evolution of Prosthetic Leg TechnologyPublished: March 23, 2022TYLER CLITES: For hundreds, thousands of years, amputation has been viewed as a procedure that’s done when there are no other options, so we try to fix it in all these different ways, and that doesn’t work. And the last thing we do is we take the leg. Because of that, not much scientific effort has been put into changing the way that that surgery is done, and so, fundamentally, the surgery hasn’t changed since, really, the Civil War era.Now, to understand the limitations of traditional approaches to amputation, it’s critical to first understand how our limbs work normally.Muscles in our limbs work in tandem with each other, with each pair joined by a tendon. So, when I bend my wrist, muscles on one side contract, and complementary muscles on the opposing side stretch. Or, when I point my foot up, a muscle in the front of my leg contracts and a muscle in the back expands. Sensory nerves, located in muscles and joints, called “proprioceptors,” detect each stretch and contraction and send signals to the brain, via the nervous system. The brain actually uses this awareness of the movement of those muscle pairs and creates a spatial, almost visualized, map of where the limb is in space. This feedback is how we sense the motion of our limbs and joints and their position with exceptional accuracy. It’s how I can touch my nose with my eyes closed or walk up a flight of stairs, without having to look down at my feet. We call this “proprioception,” and it’s essential for our ability to move naturally.SHRIYA SRINIVASAN: Proprioception is our ability to sense the world around us. It’s the way that we know our joints move in space, how fast they’re moving, how hard they’re pushing, how stiff they are. The amputation paradigm today basically throws sand over the whole thing and calls it a day. And so it leaves all these wires just hanging. Nothing’s connected properly.MATT CARTY: In a standard below-knee amputation, there’s an incision that’s made in the front part of the leg. And we go down, and we, basically, we cut the bone. And the tissues in the back part of the calf are left a bit longer and essentially are able to flap up and provide coverage at the end of the limb. That muscle flap turns into a big ball of scar.It provides good padding, but the muscle pairs are no longer connected, leading to the loss of proprioception in the residual limb. If that patient thinks about moving their phantom ankle, muscles in the front part of their leg may contract, but the ones in the back no longer stretch in connection, and vice versa. This causes the brain to receive conflicting and confusing signals, creating all sorts of issues for the patient, including phantom limb pain and difficulty using the newest prosthetic limbs.HUGH HERR: So, my limbs were amputated, obviously, in the conventional way. What that means is the muscles in my residuum, here, were stitched down at constant length. When I try to move my foot ankle, it feels like my feet are in rigid ski boots.TYLER CLITES: Now, we have all this technology. We have advanced robotic limbs, we have advanced ways of talking to nerves and muscles, and yet we’re still doing amputation the same way. So, our goal in designing this procedure was to fundamentally change the way that amputations are done, to optimize the limb for communication with an advanced external robotic device.HUGH HERR: The inception of the idea came from little domains of knowledge of how, A, the musculoskeletal system works, linked to the nervous system, and, B, knowledge about how the body is controlled and how robots are controlled. And I also knew that the fundamental motor unit of biological systems is not one muscle, but two muscles working in agonist-antagonist pairs. It’s fundamental to how we work as humans.So, one day I just thought of, “Let’s link them and take two motor nerves and get the motor nerves to grow in and create a little biological joint.” My level of education and surgeries is almost zero. So, I did not know what was possible.MATT CARTY: How are you feeling? Yeah, they just got the I.V. in you?Okay.HUGH HERR: It was around then that I met Matt Carty.MATT CARTY: Hugh and I were both interested in revamping limb amputation, and ultimately decided to focus, at least in part, on how we restore proprioception. We had done a series of early conceptual drawings and discussed the idea of creating a biological joint to maintain the muscle pairings typically lost during amputation. Using tendons and bones we typically throw away, we designed a series of pulleys and small pivot points to connect muscles, so that they work in the dynamic way they were intended to by nature.Our hope was that by restoring proprioception, patients would not only be able to perceive where their phantom limb was in space, but actually would be able to better use a prosthesis that was specially adapted to their modified limb.

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The Evolution of Prosthetic Leg Technology

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This robotic hand can partially restore a sense of touch

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Increasing Access to Brain-Controlled Prosthetics

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Support Provided By

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This robotic hand can partially restore a sense of touch

Augmented

Increasing Access to Brain-Controlled Prosthetics