Making Prosthetics More Lifelike

01 Jul.,2024

 

Making Prosthetics More Lifelike

David Brockman, a retired CalFire captain and avid outdoorsman, built a deck in the backyard of his home last year, without the use of his dominant right hand, which he lost in an accident. The prosthetic hand he used instead was a crude but functional steel hook-and-harness device.

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Brockman has tried other artificial limbs, including a high-tech prosthesis called a myoelectric. It looks like a hand and works by using electrical signals from muscles in the forearm. But that one just didn&#;t work for him.

&#;It&#;s uncomfortable, and it doesn&#;t function well,&#; Brockman said. &#;It looks nice. It&#;ll open and close, and I don&#;t have to wear a harness. But to be what I am &#; very physical &#; and to be outside working in the yard, raking, doing things like that, it doesn&#;t work.&#;

David Brockman, a retired firefighter and hand amputee, shows off his new myoelectric prosthetic device. UC Davis surgeons performed targeted muscle reinnervation surgery and used smart prosthetics to provide better muscle control, improved sensory feedback and less limb pain for amputees. (Gregory Urquiaga/UC Davis)

Rejecting his myoelectric wasn&#;t unusual. Despite the advancements in robotics and other high-tech prosthetics, a recent study found that 44% of arm amputees abandon their devices.

&#;Even though there&#;s amazing dexterous devices that can move in all sorts of ways and look similar and operate similar to an intact limb, being able to tell all of that robotic system how to move and what you want it to do is really where a big barrier is currently in the field,&#; said Jonathon Schofield, assistant professor in the Department of Mechanical and Aerospace Engineering at UC Davis.

Schofield is part of a team of engineers, scientists and surgeons at UC Davis working to make life easier for amputees through a combination of surgery, advanced machine learning and smart prosthetics. Their goal is &#;prosthesis embodiment,&#; to get these devices to mimic a biological limb so amputees gain better muscle control and sensory feedback without increased complexity.

&#;We&#;re trying to fill that gap,&#; Schofield said. &#;We&#;re asking how can we allow someone to think about making a pinching motion or think about making a fist with their missing hand and just let the prosthetic limb do that for them.&#;

Advancing Prosthetics in the Lab at UC Davis

Brockman is taking part in an experiment to help the UC Davis group and other researchers advance prosthetics. He now has a new myoelectric prosthetic hand, one much closer to the real thing. It looks like a glove and its fingers can move independently.

Brockman said the new prosthetic hand will make a huge difference in his life.

&#;For me, I love the outdoors. This is a dream come true because I&#;ll be able to grab my fishing pole and reel and grab things again instead of trying to hook it and it keeps slipping off,&#; he said.

Advanced prosthetics difficult to operate

But myoelectric devices, which use muscle activity from the remaining limb to operate, still require a lot of effort to get them to work, said Laduan Smedley, a certified prosthetist orthotist at UC Davis Health.

&#;I describe it somewhat like Morse code,&#; Smedley said. &#;Amputees have to memorize these kinds of patterns of flexion and extension or co-contraction to operate the hand.&#;

One of the newer myoelectric prosthetic hands sits on a workshop table at UC Davis Health. The smarter prosthetic operates like a bionic hand, with five fingers that can move independently. (Gregory Urquiaga/UC Davis) UC Davis Health certified prosthetist orthotist Laduan Smedley is making sure the sleeve of David Brockman&#;s prosthetic hand fits correctly. (Gregory Urquiaga/UC Davis)

Some of the more advanced myoelectric hands are more intuitive but require a smartphone app to select the desired type of grasp, such as pinching or gripping.

The UC Davis research group wants to incorporate what scientists know about how humans learn and control movement, said Wilsaan Joiner, a neuroscientist and professor in the Department of Neurobiology, Physiology and Behavior in the College of Biological Sciences.

&#;If you&#;re not utilizing what is a natural ability or natural infrastructure of our motor system to control an external device, it&#;s probably going to be incredibly difficult and nonintuitive to learn how to do,&#; Joiner said.

Read more stories on how UC Davis confronts today's most challenging health problems.

Amputations improved by targeted muscle reinnervation

Surgeons have led the way to make myoelectric devices easier to use. Not long ago, the standard amputation could still leave patients in a lot of pain. Surgeons cut bone, muscle and nerves to remove a limb. They buried those nerves under muscle or in bone to prevent their endings from growing toward the surface of the skin.

&#;The idea was that if you bury it far away from the skin then patients don&#;t get pain,&#; said Clifford Pereira, an associate professor in the Department of Surgery at UC Davis Health. &#;We found that despite doing that, people still get chronic pain and phantom pain.&#;

Phantom pain can feel like cramps or burning where the limb used to be. Many patients still develop neuromas, where nerves can grow to form a lump of painful disorganized nerve tissue. The pain from neuromas can also make wearing a prosthetic device impossible.

Surgeon Andrew Li shakes the prosthetic hand of former patient David Brockman, a retired fire captain, who had targeted muscle re-innervation surgery on his amputated hand. (Gregory Urquiaga/UC Davis) Cliff Pereira and Andrew Li are both with the Department of Surgery at UC Davis Health. They have performed targeted muscle re-innervation surgery to help amputees control prosthetic limbs more intuitively. (Gregory Urquiaga/UC Davis)

Recently, UC Davis surgeons began using a procedure called targeted muscle re-innervation, or TMR. The surgery reroutes severed nerves so that signals from the brain that once controlled the missing limb are picked up by a nearby muscle.

Pereira said it&#;s like converting a dumb muscle into a smarter muscle. Amputees only need to think about making a fist or opening their fingers for the movement to occur.  

&#;It was originally done to increase the number of muscle signals that a patient could generate after an amputation so there could be more degrees of control of a prosthetic device,&#; said Andrew Li, an assistant professor in the Department of Surgery at UC Davis Health. &#;An unintended benefit was that those patients also tended to have reduced phantom pain and neuroma pain as well.&#;

Advancing Prosthetics in the Hospital at UC Davis Health

Artificial intelligence now used in prosthetic technology

Brockman had TMR surgery at UC Davis Health and is now using a smarter prosthetic device.

&#;They actually call it a bionic hand,&#; Brockman said. &#;It&#;s a working, functional hand. It has five fingers. It&#;s got like 13 sensors built into the sleeve. And it works off a muscle reaction in my arm. So, when I twitch my thumb nerve, which is still there, the prosthetic senses that and the thumb will move.&#;

The prosthetic hand must first learn how to read these signals. This is where artificial intelligence, or AI, plays a role.

The UC Davis researchers are examining the muscle firing patterns of Brockman and others who have had TMR surgery.

Neuroscientist Wilsaan Joiner points to an ultrasound machine. Scientists are using both ultrasound and electromyography, combined with AI, to make prosthetics easier to control. (Gregory Urquiaga/UC Davis) Engineer Jonathon Schofield, left, and neuroscientist Wilsaan Joiner, right, are both working to make prosthetic limbs more intuitive by incorporating what scientists know about how humans learn and control movement. (Gregory Urquiaga/UC Davis)

Inside a UC Davis lab, Schofield attached electrodes to Brockman&#;s forearm using an electromyography machine, which records the muscle&#;s electrical activity. He asked Brockman to make several different hand gestures, and the computer&#;s programming begins to recognize those patterns.

Electromyography can sometimes confuse electrical signals from other muscles, so the scientists are also using ultrasound machines that use sound waves to produce images. When Brockman contracts a muscle, it becomes denser and bounces back more sound.

The researchers are combining all this technology and data with AI in the hope that prosthetics will become more intuitive for the user. 

&#;We&#;re leveraging artificial intelligence, machine learning algorithms that are looking at the muscles that remain in that person&#;s residual limb,&#; Schofield said. &#;It&#;s learning what that activity looks like when amputees wanted to pinch or make a fist or make a pointing motion.&#;

Can prosthetics &#;feel?&#;

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Surgeons are hoping to advance prosthesis embodiment by enabling users who lost their sensory nerves to gauge temperature and pressure. They may be able to do with sensory nerves what they did with motor nerves in the targeted muscle re-innervation surgery &#; connect the severed ones with those in the overlying skin. If the artificial hand is touched or gets hot, it sends that signal to the skin of the amputee.

Amputees also have difficulty sensing body position and movement with a prosthetic device. But researchers said one way to overcome that is to integrate prosthetic devices into the body, like a human machine. The concept, called osseointegration, is the next step in smart prosthetics.

Peyton Young, a UC Davis Ph.D. candidate in Jonathon Schofield&#;s lab, demonstrates how electromyography works using a robotic arm. The robotic arm recognizes the electrical signals from his forearm muscles and it moves accordingly. (Gregory Urquiaga/UC Davis)

&#;Osseointegration is making the prosthetic device essentially heal into the bone and become a weight bearing proprioceptive structure,&#; said Li, the UC Davis hand surgeon. &#;You can still take it off, but it&#;s much more a solid component of your body that could potentially make things a lot more intuitive, a lot more natural, like picking up heavy things, doing pull-ups potentially.&#;

The Integrum OPRA osseointegrated implant for above knee amputations is Food and Drug Administration approved and allows direct integration between bone and the surface of a prosthetic device. UC Davis is now actively recruiting patients for the surgery.

David Brockman with his wife, Tereasa Brockman, at UC Davis after David had a fitting for his prosthetic hand. (Gregory Urquiaga/UC Davis)

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Overview of Limb Prosthetics

A limb prosthesis is an artificial limb that replaces a missing body part, usually because it has been amputated.

The main causes of limb amputation are

  • Blood vessel (vascular) disease, particularly from diabetes or peripheral arterial disease

  • Cancer

  • Injury (for example, from a motor vehicle crash, work-related accident, or military combat)

  • Birth defect

In the United States, approximately 1 in 200 people are currently living with the loss of a limb, and approximately 500 amputations are done each day. This percentage is likely to increase because, as the population ages, more people will develop diabetes and vascular disease.

For people who have had an amputation, a prosthesis (artificial limb) is often recommended to replace that body part. At a minimum, a prosthesis should enable the person to perform daily activities (such as walking, eating, and dressing) independently and comfortably. At best, a prosthesis may enable the person to function as well or nearly as well as before the amputation.

Success with a prosthesis is most likely to occur when the clinical team involved has many different types of professionals, depending on the person&#;s needs. At a minimum, core team members include the surgeon, prosthetist, and physical therapist. Prosthetists are experts who evaluate the person's overall functional capabilities and develop a prosthesis treatment plan, which includes designing, fitting, fabricating, and adjusting the prosthesis and providing lifetime follow-up care to maintain the prosthesis and provide advice and instruction on care. For more complex cases, the team could also include a physiatrist, occupational therapist, social worker, psychologist, and family members.

People may have concerns regarding passing through airport security with a prosthesis. Security personnel typically do not ask people to remove a prosthesis. If they do, they are obligated to do this in a private setting, because it usually requires removing some clothing. It may be useful for the prosthetist to write a letter stating that the prosthesis has metallic and microprocessor components and that leaving the prosthesis off for more than 10 to 15 minutes could make it difficult to put it back on because the fluid volume of the residual limb will increase.

Goals

Goals range from simple mobility to being able to do high-impact activities, such as running and jumping. The prosthesis' components are customized to help people achieve their different goals. Advances in cushioning materials, prosthetic socket design, and foot, ankle, knee, hand, wrist, and elbow component technology have significantly improved comfort and function. When fitting a prosthesis, the prosthetist works to make sure that the person is comfortable, stable while standing and walking, and able to or achieve individual goals.

Highly motivated, otherwise healthy people with a prosthesis can accomplish many extraordinary feats (for example, go skydiving, climb mountains, complete triathlons, fully participate in sports, or return to demanding jobs or to active duty in the military). Whether a prosthesis is used only for basic mobility or for more demanding activities, it can provide profound psychologic benefits and improve quality of life.

Successful prosthesis use depends on the following:

  • The person's other medical conditions

  • The person's physical and cognitive capabilities

  • The characteristics of the residual limb

  • How well the prosthesis socket fits and connects to the body

Prosthesis fitting is a specialized skill. Also it can be hard for people to make the physical and mental adjustments necessary to function with the prosthesis. Thus, the whole process of selecting and adjusting components and assessing overall prosthesis function is challenging and takes significant time. Not all people are candidates for all types of prostheses.

Amputation levels

An entire limb or part of one may be amputated. Doctors weigh many factors when amputating a limb. It is very important to

  • Remove dead or infected tissue

  • Ensure there is good blood flow in the residual limb

Other important considerations are to

  • Preserve muscles and their attachments to bones as much as possible

  • Stabilize bones

  • Cover the end of the residual limb with muscle

Preparing for an amputation

Having an amputation is difficult for people. Losing a limb is not only physically challenging, but people's self-image often changes after they lose a part of "themselves." Doctors and prosthetists try to prepare people and their family by explaining why an amputation is necessary and what will happen before and after the amputation and during the prosthesis fitting process. People who understand the process and have realistic expectations of the difficulties they may face and the most likely outcomes are more likely to persevere and have a better result. Doctors sometimes arrange for the person to talk with someone who already has an amputation and has adjusted well to it.

Before doing surgery, doctors try to get people in the best possible medical condition. They try to address existing medical problems, such as poor nutrition, diabetes, and heart or lung disease as much as possible. Because smoking interferes with healing, smoking cessation measures are important. If time permits, people who are weak or debilitated may do therapy and exercises to make them stronger and more flexible.

After surgery

Immediately after surgery, the medical team starts measures to

  • Maintain range of motion of joints to prevent them from becoming stiff

  • Maintain or increase the person's strength and general conditioning

  • Manage swelling (edema) in the residual limb

When recovery permits, people should begin to desensitize the end of their residual limb by massage, tapping, vibration, and starting to bear weight on it.

Prosthesis fitting can begin when the surgical wound is sufficiently healed and the swelling has gone down enough, provided that the person has enough overall strength and joint range of motion. Prosthesis fitting usually occurs approximately 7 to 10 weeks after amputation.

The residual limb continues to change for 6 to 18 months after amputation as more fluid leaves the residual limb and the muscles reshape. While these changes are ongoing, prosthetists may fit one or more temporary sockets until the residual limb stabilizes. When the residual limb seems close to its final size and shape, prosthetists fit the person with a definitive prosthesis. A temporary prosthesis allows people to become accustomed to pressures and forces involved in using a prosthesis.

Early rehabilitation facilitates recovery and future success in using a prosthesis (see Rehabilitation After Limb Amputation). When possible for people whose amputation is scheduled, rehabilitation begins before the amputation. For people whose amputation is done suddenly (for example, because of injury sustained in a motor vehicle crash or combat), rehabilitation is begun as early as the first day after surgery.

More Information

The following English-language resources may be useful. Please note that The Manual is not responsible for the content of these resources.

  1. Amputee Coalition: Information to promote limb loss prevention and provide education, support, and advocacy for people affected by limb loss

  2. U.S. Department of Veterans Affairs: Rehabilitation and Prosthetic Services: Resources regarding national policies and programs for medical rehabilitation and prosthetic and sensory aids services that promote the health, independence and quality of life for Veterans with disabilities

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