The World of Prosthetic Limbs
There’s no such thing as a disabled, broken human being.
The built environment, technology, is broken and disabled.
— Hugh Herr, MIT
In Superhuman Body, Ty Duckett captured our hearts with his sincere story of growth and change—an evolution that he says happened after he lost a leg to a motorcycle accident. Ty, an accountant and auditor who wasn’t particularly athletic before his accident, is now an award-winning adaptive surfer, runner, and volunteer who helps kids learn to surf. “As counterintuitive as it may seem, this tragedy helps me see the brighter side of things,” Ty says. “It helps me be thankful for every moment, every minute, every opportunity to live. So that’s the stoke that I want to pass on.”
As we prepared for the film, Ty took us through his story—including the challenges of finding not just “the right” prosthetic device, but several, based on the array of sports he now participates in. We learned that he is not the first, and he will not be the last, to navigate what can be a confusing, time-consuming, expensive, and sometimes painful process. Happily, we also learned that researchers and technicians around the world are innovating in the world of prosthetics. People are “building a better mouse trap”—producing everything from more affordable prostheses, to bionic devices, to fashionable but functional arms and legs, to high-tech limbs controlled by brain signals.
Hugh Herr, Director of the Biomechatronics group at the MIT Media Lab, is one of those innovators. As a double amputee—with the coolest bionic legs ever—he’s set a goal that, if widely adopted, would change society as we know it. “The goal is to create a world in which one can go through a traumatic injury—and experience limb amputation or paralysis or various other conditions—and because of fantastic technology, not experience a disability,” he says.
Reaching this goal requires an initial paradigm shift in our collective ideas about “disability,” including:
- We change our definition of accessibility. The environment we build, and the way we solve problems, both need to flex around the needs of all humans—not the other way around.
- We change our thoughts and policies around how to support people with limb differences or other conditions that usually require individual adaptations.
- We create new understandings and technologies to redefine what “able” looks like.
- We create new understandings around the importance and necessity of prosthetic devices for anyone with limb difference who wants one.
- We make access to prosthetic devices easier and more affordable.
Herr calls his fantastic technology “bionic limb reconstruction.” He’s already researching methods that will allow both arm and leg prostheses to capture and replicate “biological behaviors.” In other words, at the highest levels of prosthetic device engineering, a person with a limb difference will be able to function as if there were no difference. In some cases, the person will be able to function even better than biology would naturally have allowed. “This will be a really pivotal point in history,” Herr says, “where you can get a leg amputation or arm amputation and not experience a disability.”
A Bit of Perspective
Archeologists have discovered an Egyptian mummy with a wooden toe—a 3,000-year-old prosthetic device, and so far the earliest example of such technology. A lot has happened since[1]:
- “Early” prostheses were controlled by cables that would extend or retract an arm or leg.
- Today, most prosthetic devices are not the state-of-the-art game-changers that Hugh Herr is making. In fact, the most common type are still “myoelectric”—they rely on “electromyography” (EMG) signals from the residual limb muscles for control. Sensors interpret muscle contractions, convert them to electric signals, and then use those to control movement. The problem with myoelectric devices is that the most someone can reliably accomplish is to open or close a prosthetic arm—but complex maneuvers, like moving individual fingers or rotating the wrist, can’t happen. Without the muscles that control these movements, there are no EMG signals to use.
- The next level of development is “targeted muscle reinnervation” (TMR), where nerves are connected to remaining muscles within a residual limb or the chest. The problem with TMR is that the wearer of a prosthetic device has to undergo lengthy and exhausting training to refine movements, but still, the movements feel unnatural.
- More than fifty million people live with limb amputations worldwide. According to a 2017 study, only about 5 percent have access to prosthetic devices because of high costs and other barriers. It’s this reality where today’s innovative researchers are working—both to improve the experience of those who wear prosthetic devices, and to make them more accessible and affordable.
Some of the Coolest Tech Out There
THE BRAIN / PROSTHESIS CONNECTION — Ever since visual and cochlear implants were developed, innovators have realized that our brains and physical bodies can communicate through creating new connections. So far, the sensations people experience when using these devices might not be as natural as those produced by biological eyes or ears—but our ability to restore even distorted sights or sounds for those who prefer this functionality is really remarkable. It’s not surprising, then, that researchers have broadened their horizons, by creating prosthetic limbs that work in conjunction with brain signals. They’re even attempting to restore function to paralyzed limbs[2].
All of this neural technology is cutting-edge. It might involve brain implants, rerouting nerves to new locations so a device can access them, or fusing a prosthetic fixture onto the skeleton and connecting directly to nerves. Again, up to now, the intuitive control of these prosthetic limbs isn’t complete. Full dexterity, sensation, and strength of a biological limb cannot yet be replicated, but the neurons that control a biological limb—and often create “phantom” pain after an amputation—can be repurposed to operate the prosthesis.[3] As engineers continue to create machines that duplicate natural movement and function, their mission will be to increase “real” functions and feelings.
ARTIFICIAL INTELLIGENCE — AI is another key component to the advancement of today’s most advanced prosthetic devices. Its job is to record the muscle twitches or nerve impulses made by the wearer—which translate to movements in the artificial limb. As AI improves, its ability to collect this data, “remember it,” and then translate it into movement will increase. Now, for example, the wearer of an artificial hand often has to consciously think “I’m going to pick up that can,” and then twitch instructions to the arm, and after a few seconds, the hand can open and fingers can “sense” the can. Soon, once AI learns a person’s signals, then the “automatic” movement of picking up a can will be much more likely.
Some current AI developments include[4]:
- A prosthetic hand that uses computer vision to identify an object, and then adjusts the hand’s grip without manual intervention from the user.
- For wearers of a prosthetic leg, sensors on the residual hip muscle can determine the user’s intended movement—and then AI bends the prosthetic knee and adjusts its swing. This automatic assist adjusts to the walker’s stride and allows for more natural movements, even including jumping, navigating stairs, or walking on uneven ground.
- By using the remaining biological limb, AI can learn how that brain-limb communication works. AI records how the brain tells the body to make usual movements. An “AI decoder” uses this information in the prosthesis on the missing limb; it can even recognize several movements at once, such as pinching, which requires coordination between thumb and forefinger.
- The future of AI will include full sensory feedback—heat, softness or hardness, and other features of an object or surface. This involves establishing a connection between the prosthetic device and the somatosensory system—how we perceive touch, pressure, pain, and temperature.
CHANGING HOW WE WALK—AND RUN, AND DANCE, AND… — Dr. Herr’s Center for Bionics is on the cutting edge of innovation in the field of prosthetic devices. Among his inventions are leg exoskeletons and a powered ankle-foot prothesis called EmPower, which allows amputees to walk with a natural gait. It was the first leg prosthesis in history to so successfully emulate the action of a biological leg; the wearer’s walking speed and metabolism got “back to normal.” Since its introduction, companies around the world have introduced microprocessor-controlled knees (also known as bionic, or computerized knees), several bionic foot and ankle components, and all-in-one “connected” limb systems that continuously capture data on the terrain and adapt as you’re walking.
In addition to these very high-tech options, engineers also have created more choice in what might appear to be lower-tech needs. For example, the carbon fiber running blades used in the Paralympics—and by runners who are not competing, too—are “simple” curved blades that compress and rebound when the wearer takes a step. These, along with “walking feet,” or specialized feet for surfing, or running on rough terrain, can be swapped out. While many athletes still require several different leg systems—entirely different prostheses for each activity—designers envision a not-too-distant future where many athletes will be able to choose a single device with a universal fitting onto which a variety of sports or walking feet can be snapped into place.
“I’ve got a few different legs,” Ty says. “I have a running leg that’s like a blade, and I have a walking leg, and two surf legs. My new surf leg has a bending portion, and the knee actually came from my running leg; my other surf leg is static. It’s like a kickstand. That’s what I’m most familiar with. My walking leg, that is a whole different monster, because it has microprocessors. It kind of knows where I’m going—like, it knows where I am in space.”
Many of these innovations were inspired by designers who were assisting athletes to custom-design prosthetic limbs—or by athletes who made their own. The more collaborative the field becomes, the more specialized, interchangeable, and customizable these day-to-day devices will be.
“I’m excited about the possibilities of prosthetics in the future,” Ty says. “I saw something where an arm amputee put on a prosthetic device that had sensors in it, and when they would flex their muscle, it would flex the fingers of the hand. When I see stuff like that, I’m just like, wow, that would be amazing if I could flex a muscle and then my leg extends, or flex a muscle and my foot extends. It seems like sci fi, but this could actually happen. I’m doing my research on these folks and I can’t wait to connect with them.”
AMAZING ARMS — As shown above, bionics, neural integration, and AI have entered the world of prosthetic development for upper limbs too; in fact, finger movement and sensitivity are some of the most accessible indications of success in the field in general. Everyone can relate to needing dexterity in their hands.
However, arms are also one of the ways in which those with limb difference, especially young people, can express themselves. Because children and teens grow so fast, fit and comfort of prostheses can be extremely variable—and kids grow out of their prosthetic arms more frequently than adults do. If these devices are expensive, and if fittings and appointments take a long time to conclude, then both access and functionality can be greatly diminished. That’s why it’s so fun to see several companies creating arm prostheses that can be used for daily activities and sports—and have style. For example, one company, called Hero Arms, makes lightweight, breathable, affordable, bionic, and aesthetic arms that come in a range of cool designs and colors. Some of them look like superhero arms!
Navigating the Process
“I used to joke when my accident first happened,” Ty says. “I used to say if it was ever a good time to lose a leg, I picked it. And I only say that because of technology—because of how it is today.”
If limb difference is acquired—after birth, from illness, trauma, or amputation—then the process of navigation begins with physical and emotional healing. If limb difference is either acquired or congenital, then families must gather their support systems and research medical resources—not to mention managing financial concerns, insurance coverage, possible housing adaptations, and myriad practical realities. Thankfully, designers and engineers around the world are helping with the next phase of navigation. They’re prioritizing making available to more people, regardless of their rural locations or financial resources, detailed information, research, and the prosthetic devices themselves. Two nonprofit organizations focus on helping individuals with healthcare support; the first is targeted at those who cannot otherwise afford prosthetic care or devices they need (Limbs for Life); the second is more general (NeedyMeds).
As this amazing age of technological change continues, new advancements are happening every day—and anyone on the journey into life with a prosthesis can find great information from dozens of medical providers and research facilities. However, for those just starting out, one great place to begin is this fact sheet by the Amputee Coalition: “Prosthetic FAQs for the New Amputee.”
Below, we’ll summarize a few of the main areas of concern that our experts told us about, and with which the Amputee Coalition can assist.
HEALING — Of course, “healing” includes a wide range of experiences—from physical to emotional and spiritual—and no one can predict what any given person might need during this period. However, when experts address the purely physiological aspect after amputation, they advise that most patients will experience a period of two to six months before any incision has healed and tissues have recovered. The location of an amputation on the limb, the size and shape of the residual limb, and various other factors will determine the type, functionality, and range of choices regarding future prosthetic devices. Sometimes, a temporary device can be fitted to bridge the healing process; then, more permanent solution-building can begin.
NATURAL CHANGES — After healing, everyone’s body changes over time and with natural shifts in our habits. For example, we gain or lose weight, our exercise habits change our muscle tone, and we age. All of these mean that a residual limb also can change over time—which impacts how the limb fits into a prosthetic device’s socket. In addition, throughout any given day, the muscles and tissues in the arms and legs also change based on the weather, our activity levels, and other factors, causing the residual limb to swell or contract. Being aware of the dynamic nature of the body helps a patient to consider the type and adjustability of prosthetic devices.[5] The Amputee Coalition also gives advice as to how to prepare for a prosthesis and how proceed if your prosthesis doesn’t fit correctly.
GOALS — Not everyone is Ty. Not everyone wants or needs a universal attachment that will allow quick changes between a mountaineering foot and a walking foot. So being clear about your desired activities, your pain levels, your mobility challenges, your pre-amputation habits and skillsets, and other factors will help you define what kind of prosthetic device to shoot for. Also, your goals might change as you get used to your new body, the equipment, and what life has to offer. Johns Hopkins Medicine says that most leg amputees who wear a prosthesis get a new prescription every three to five years. They call it “outwalking” one device—when you’re body has changed enough, or you’re moving differently with more experience, so that the device you’re used to is no longer doing the job[6]. For those with arm prostheses, it might be time for a change when a young person has reached full adult size, and a prosthesis won’t have to be switched out as frequently—or if specific characteristics of a prosthetic device are more applicable to your life. For example, a chef we researched prefers the metal “claw” hand, so that he can use it on hot stoves and pans; others prioritize having the most dexterity possible.
COSTS AND INSURANCE — In general, insurance plans do cover at least some of the costs of a prosthetic device, but the process can be laborious. The Amputee Coalition advises communicating directly with your insurance company, documenting everything with your healthcare provider, and bundling costs for the device itself with the several appointments for fittings and alignment adjustments. Your provider also will be working with a “K Level,” which is a 0 – 4 scale used by Medicare to rate a patient’s rehabilitation level. A level of 0 indicates that a prosthetic device will not enhance a patient’s quality of life or mobility; Ty is a level 4—someone whose prostheses must exceed basic stress or energy levels.
Resources
Amputee Coalition, amputee-coalition.org
The American Orthotic and Prosthetic Association, aopanet.org. This organization’s site includes a list of patient resources, as well as a lot of information that impacts the industry. It works with government agencies and provides background on upcoming legislation affecting amputees.
Limbs for Life, libsforlife.org. This global nonprofit is dedicated for providing fully-functional prosthetic care for individuals who cannot otherwise afford it—along with raising awareness for amputees’ challenges.
NeedyMeds, needymeds.org. Another nonprofit, NeedyMeds provides more generalized services that connect patients with affordable healthcare.
The Limb Preservation Foundation, limbpreservation.org. This is an independent nonprofit serving patients in the Rocky Mountain Region—supporting the prevention and treatment of limb-threatening conditions. They provide all kinds of support, including prosthesis resources, at: https://limbpreservation.org/business-directory/wpbdp_category/amputee-prosthesis-resources/.
Heather Mills, heathermills.org. Heather lost her leg to a landmine in 1993. She hosts a comprehensive website with a database for care, fundraising tools, and the latest on prosthetic technology.
The O&P (Orthotic & Prosthetic) Edge, opedge.com. This informational website is targeted toward professionals in the field, but there is a lot of research here for everyone.
[1] Marijan Hassan, “How AI is Helping Power Next-Generation Prosthetic Limbs,” Wevolver (website), posted online 23 January, 2023, https://www.wevolver.com/article/how-ai-is-helping-power-next-generation-prosthetic-limbs.
[2] Sarah Collins, “‘Biohybrid’ device could restore function in paralysed limbs,” University of Cambridge (website), published online 22 March, 2023, https://www.cam.ac.uk/stories/biohybrid-device#:~:text=Researchers%20have%20developed%20a%20new,the%20brain%20and%20paralysed%20limbs.
[3] Luke Hurst, “‘Groundbreaking’ bionic arm that fuses with user’s skeleton and nerves could advance amputee care,” euronews.health (website), published online 10 November, 2023, https://www.euronews.com/health/2023/10/11/groundbreaking-bionic-arm-that-fuses-with-users-skeleton-and-nerves-could-advance-amputee-.
[4] Hassan.
[5] Kiyomi Taguchi & James Urton, “Video: Finding—and keeping—the perfect fit for a prosthetic leg,” UW News (website), University of Washington, Health and Medicine, published online 13 October, 2022, https://www.washington.edu/news/2022/10/13/sanders-lab/.
[6] Johns Hopkins Medicine, “What You Should Know Before Getting a Prosthetic Leg,” Johns Hopkins Medicine (website), Wellness and Prevention, accessed 16 May, 2024, https://www.hopkinsmedicine.org/health/wellness-and-prevention/what-to-know-before-getting-prosthetic-leg#:~:text=Common%20obstacles%20include%3A,the%20fit%20of%20the%20socket.