One of every 200 people in the United States has lost a limb, and each day nearly 500 more people will lose one. Those numbers could double by 2050, according to recent findings from the Amputee Coalition.
Although advances in prosthetic technology have improved function in patients with limb loss, some believe an amputation reduces quality of life. A brain-controlled prosthesis could quell those beliefs; however, the idea of amputees using their thoughts to walk could seem like science fiction. It may not seem that way much longer.
“It is important for people living with disability to get…out of the hospital, out of therapy and back to normal life,” Justin Sanchez, PhD, program manager at the Defense Advanced Research Projects Agency (DARPA), told O&P Business News. “With new technologies developing…we are trying to take that to a new level – take the impossible and make it reality.”
Enter neuroprostheses. As strides are made in engineering and neuroscience, brain-controlled devices are edging closer to clinical reality.
Innate control and innovative devices
A neuroprosthesis is a small-scale device typically implanted in the brain or on the skull of a disabled user. It uses electrical currents that interface with the nervous system and read intentions of the brain. The intentions range from basic levels of control to high-level commands, such as driving a wheelchair or controlling a prosthetic limb.
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Since the devices are commonly placed under the skin, brain activity and intended motion are more accurately read, Blair Lock, MSCE, bionics researcher at the Rehabilitation Institute of Chicago and Coapt chief executive officer, told O&P Business News.
“The closer you are to the source of the data, the better that information is to provide to the [assistive device]…[and] to provide an intuitive level of control,” he said.
That control holds many benefits, but some say it is not available in O&P, Jonathan Naft, CPO, general manager of Myomo Inc. and founder of Geauga Rehabilitation Engineering Inc., told O&P Business News.
“There are those in the industry who would say our devices are not true neuroprostheses,” he said. “In O&P, current devices are not directly controlled by the brain. That mostly exists on a research level.
“We are picking up [electromyography] EMG signals that come from muscle. So although the signals are indeed starting at the brain, they are not solely controlled by the brain; they are indirect.”
But many O&P devices are a subset of neuroprostheses and considered the closest thing commercially available, he added. These are known as myoelectric prostheses.
Since muscles can transmit EMG signals, sensors can be placed on the residual limb, allowing a user to control the prosthesis by attempting different movements, Naft said.
“The electrodes sit on the patient’s skin…[and] read the energy coming from the muscle,” he explained. “The brain sends a signal to the arm to move, the muscle attempts to move and an EMG byproduct is produced.”
“By using these signals…we can decode how the person is trying to move the prosthesis, and then activate it,” Levi Hargrove, PhD, director of the Neural Engineering for Prosthetics and Orthotics Laboratory at the Rehabilitation Institute of Chicago told O&P Business News. “That is how it works. The control is purely the result of the patient’s intention, so some consider it a type of neuroprosthesis.”
One unique benefit of myoelectric devices is their ability to reduce the amount of wear and tear on a limb commonly caused by overuse of body-powered prostheses. There are many more benefits, Gerald Stark, MSEM, CPO/L, FAAOP, Ottobock senior upper limb clinical specialist, told O&P Business News.
“The big thing is that myoelectrics encompass so many new areas including pattern recognition, sense of feel, kinesthesia and someday even embodiment.”
Pattern recognition uses information from dozens of muscle signals to simplify command of the prosthesis, while offering the user innate control, Stark said.
“The user is able to control the prosthesis just by trying to do the natural movement,” he said. “As long as they do the action repeatedly – like moving their wrist up or palm down – the prosthesis actually adapts itself to them so they don’t have to isolate muscles [as typical with a body-powered prosthesis].”
Researchers are taking steps toward embodiment through re-innervation. This process threads electrodes directly into nerves of the residual limb, and stimulates them using electrical currents.
Nerves previously used to serve a missing limb are rewired to a remaining part of the limb, enabling a sense of touch.
“Think of a patient who has their arm amputated between the elbow and wrist,” Naft said. “They do not have the hand, but…inside the arm, they still have muscles that traditionally move the wrist, hand and fingers.”
“Whether the remaining muscles [in the arm] are healthy, damaged or even partially amputated, the nerves can still generate electrical signals,” Hargrove added.
“Re-innervation reroutes the nerves…that would have gone to the hand and transfers them to the biceps, for example, or the skin over top of the biceps. So when the user attempts to move their hand, when the re-innervated biceps contracts or skin is touched, it feels like you are touching the missing hand.”
Recreating life-like sensation is a tall order, Hargrove said, but myoelectric prostheses are being outfitted with more advanced sensors that can gather natural sensations or even distinguish basic features of an object. This is key for developing kinesthesia, or non-visual awareness of where a limb is in space, and would allow a user to feel the environment like never before, he said.
Not everyone is a candidate for myoelectric prostheses, Naft said. Users need to have enough healthy residual muscle to measure EMG signals, volitional control of those muscles and cognition to properly manage the device. Individuals with severe nerve damage may not benefit from myoelectrics.
“Different devices have different profiles for who they are best for, and each case should be assessed independently,” he said. “The key is [to identify] user need…then select the best technology to help them meet that need.”
Myoelectric prostheses meet the needs of most users, he said. “The beauty of this technology is that is completely safe and offers another option for those [who] choose advancing technology,” he added. “This is an exciting time in O&P.”
Strides toward the future of O&P care
If myoelectrics bring excitement to the present in O&P, true neuroprostheses will deliver in the future, Stark said. Advances in engineering are being made.
“One of the most unsung aspects are advancements in battery technology. None of this can happen without a good battery,” he said.
At DARPA, Sanchez holds the same belief, and is working to improve that technology.
“We are thinking very much about next generation systems to power implantable devices,” he said. “If someone is [using] this device throughout the course of a lifetime, you would like the battery to last as long as possible.”
Power consumption is driven by size and batteries have gotten smaller, Naft added.
“Think about the first cellphones. These things were essentially in a small briefcase. Fast-forward to today and you are carrying a computer in the palm of your hand,” he said. “Power systems have gotten more lightweight and more efficient.”
Neuroprostheses will become even more efficient with the evolution of batteries, but there could be a better way to power them, Hargrove said.
“I think the most promising approach is using wirelessly powered sensors inside the skin,” he said. “With wireless coupling…data can be transferred using electromagnetic fields. [The waves produced by those fields] are transmitted through the skin to a receiver.”
Using this method, devices would be longer-lived, reducing the need to replace a battery through surgery, he said.
Lock added that devices like pacemakers and cochlear implants have offered additional strides in the development of implantable technologies.
“I think what is exciting about engineering in O&P is that we have always been a field of leverage,” he said. “We see great developments in many different areas, and can leverage technology from other fields.”
One of those fields is at DARPA. Through the Hand Proprioception and Touch Interfaces (HAPTIX) program, researchers are exploring new areas of kinesthetic awareness and continuing efforts in sensory capabilities. These efforts could enhance natural sensation and control in neuroprostheses, but the team is pushing further, Sanchez said.
Through the Systems-Based Neurotechnology for Emerging Therapies (SUBNETS) program, they are hoping to develop direct neural interfaces as a part of a closed-loop system that restore normal brain function to service members and veterans with neuropsychological illness.
“Neural illness affects many different sub-networks of the brain…the standard of care is to talk to your therapist and they prescribe drugs, some kind of intervention or behavioral therapy,” Sanchez said. “This is not as precise as it needs to be to treat those networks.
“The goal is to develop new technology and knowledge for precision neuroprosthetic interventions. We are trying to change the game by…going directly to the root of the problem.”
The team believes that brain function can be repaired after injury, and is working to translate that concept into the clinic. SUBNETS launched in July of this year.
True neuroprostheses are well in the pipeline of O&P, and Hargrove predicts they will become commercially available within 5 years to 10 years. This will have an unequivocal impact on the amputee community, even if it is not here yet, he said.
“You could consider [this research] as sort of a stepping stone,” Lock added. “We talk about neuroprostheses, sensors the size of a grain of rice and systems [that can be] implanted into the brain.
“With the advent of more invasive technologies…this is the next generation – the first step in that future direction.”
Challenges still remain, Lock said. While neuroprostheses have gathered much attention in the experimental arena, few have transitioned to clinical use.
“This has not been on the table yet because the most invasive technology still lives mostly in research. There is a big difference between folks researching it and what practitioners can provide to their patients.”
Stark added that since neuroprostheses are a novel technology, many clinics have not been exposed to the concept, and could be hesitant to consider it.
“The issue is they are just not comfortable. We get into neuroprostheses, external power and high degrees of specialization – that takes a different kind of prosthetist…and really, patients should be seen by someone who is a specialist.”
There are also technical hurdles to be met, Hargrove said. True neuroprostheses are invasive, and in order to stimulate nerves, the devices must be implanted directly into the brain.
Inserting foreign materials into the body could introduce pathogens, cause negative immune response and open the door to infection. Even minor surgeries hold some level of risk, he said. Next-generation devices will need to be composed of innovative, biocompatible materials.
Some patients might reject neuroprostheses, Hargrove added. While the devices could offer many benefits, underlying factors could effect a patient’s decision.
“Some people might not want to go through surgery or invest in additional therapy…and might choose not to have it. It is a personal choice,” he said. “It is also a choice of clinician and physician, but in many cases it can be patient preference.”
“It may not be for someone who isn’t an early adopter of technology,” Stark added. “It takes someone…who is able to voice [his or her] concerns.
“It also takes a high degree gadget tolerance…so someone that is not going to not be frustrated if it does not work immediately. They have to have the capacity to overcome these things.”
But many who have the capacity to endure the initial hurdles, may never get the opportunity, he said.
“It is difficult to say it…but the reality is only a few patients will be able to afford these devices. The impact of neuroprostheses will create a great desire…but the biggest barrier is with health care costs.”
With novel technologies come a host of institutional oversights and financial implications, he said. While the devices could improve quality of life for amputees, some third-party payers may be unwilling to reimburse for the devices.
“We are advancing leaps and bounds with prosthetic design and technology. We can talk about these wonderful things in prostheses integrated directly with the brain…but then in the end we have to have that cold discussion of why we are trying to fit a greater volume of people with a lesser amount of money.
“We cannot give the patient everything we would like; we have to be selective, and health care has really limited that,” he said. “[To overcome these barriers], there has to be a cultural commitment…an outcry to say, ‘you cannot limit us.’ We have to make that commitment to our amputee community.”
A look forward
The O&P industry is committed, Lock said. Various hurdles will force researchers, engineers and prosthetists to push the boundaries of understanding, but strides are being made in that direction, he said.
“It is going to take an all hands on deck approach…[but] the engineers around the world do great work. The development is going to happen. There are a lot of us [in the industry] doing it.”
The National Institutes of Health spends more than $6.5 million each year on neuroprostheses research and development, according to the American Society of Mechanical Engineers.
Researchers at Case Western and Northwestern University also are engaged in clinical studies in the hopes of creating devices fully integrated with bone, tissue and the brain.
“They are making great strides even at NASA,” Stark added. “Neuroprostheses will engage multiple inputs all at the same time, and then someday they won’t just be about control. They will be about giving some sort of response like…touch or kinesthesia.”
Advances currently happening in biology, material and neuroscience will lead to smaller, smarter and energy-efficient implants, he said.
“The prosthesis is going to adapt to the patient rather than patient adapting to the prosthesis. Technology is getting better every day. This is going to change how we look at prostheses; this is going to change everything.”
Strides in prosthetic technology have been dramatic, Sanchez added, and are a sign of things to come. Engineering advances will overcome technical hurdles and financial hurdles could follow suit, he said.
As neuroprostheses transition from the lab to the clinic, it will herald a new era of restorative surgery that transforms not only the amputee community, but the O&P industry as a whole. “That is why we are pushing so hard,” Sanchez said. – by Shawn M. Carter
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Disclosures: Naft, Lock, Hargrove, Sanchez and Stark had no relevant financial disclosures.