Tomorrow's Technology: New Discoveries, New Directions for O&P

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By Judith Philipps Otto

Each year brings new technological advances in the field of O&P that do not fail to amaze and astound; their future potential fills us with hope. As O&P practitioners, therapists, physicians, and those who support them, our shared goal is to restore lost mobility to patients in increasingly effective ways--to be able to provide significantly better enablement to help improve the quality of their lives.

This is no small ambition--the new technology, means, and methods we await so hopefully do not materialize out of thin air. Researchers who focus their study on very specific aspects of biomechanical function easily can spend decades and even lifetimes in understanding the complexities of the human design and how to duplicate, supplement, or restore even limited degrees of lost function.

So when extensive and persistent effort is rewarded with success, it is truly a moment for marveling and rejoicing--especially when that success is widely hailed as a rare major breakthrough, as in the case of the Neuro-Controlled Bionic Arm pioneered by physiatrist Todd Kuiken, MD, PhD, of the Rehabilitation Institute of Chicago (RIC). The arm comes closer than any concept yet evolved to duplicating the natural human ability to simply think about a movement in order to perform it.

The bionic arm's capabilities rely on nerve transfers that allow the wearer to control simultaneous operation of six joints, including a motorized shoulder, arm rotator, elbow, two wrist movements, and a hand.

Previously, wearers of myoelectric arms could only control the movement of one joint at a time, and each phase of movement involved, for example, in the process of picking up an eating utensil and conveying a bite to the mouth could take several seconds, as each joint was separately activated and completed before the next joint adjustment was begun. However, a test subject fitted with the new bionic arm (a Liberating Technology Arm with a Boston Elbow) has demonstrated his ability to move the arm with more natural, intuitive control and greater ease--simply by thinking about it. And he reports that the more he uses the arm, the easier and more automatic the response to his thought becomes.

He puts his hat on--which is no small feat for a man with bilateral shoulder disarticulations. He can pick up and set down a glass of water or even an egg.

Prosthesis 'Feels' with Transferred Nerves

This facility of function is made possible by nerve transfer surgery that allows the subject to use his brain to send a message to the four primary nerves that originally controlled his arm and hand movements. Although those transferred nerves are no longer positioned in the original arm, but fastened just beneath the skin on his chest, the subject's prosthesis contains sensors that receive the signals from the re-innervated chest muscles and, in turn, sends the signals to a forearm computer that controls the six motors in the prosthesis.

The brain receives sensations that it recognizes as coming from the hand, and responds with the speed we take for granted--controlling the hand's responsive movements with the speed of thought, based on the impulses received.

Key to the nerve transfer's success is the potential to "feel" what the subject is holding with the prosthesis as if it were in his or her missing hand. Hand sensation nerves have grown into his chest skin, thus the brain receives sensations that it recognizes as coming from the hand. Experiments have been done linking this to what the prosthesis touches--essentially letting the amputee feel what he is touching as if it were in his missing hand.

"It's kind of like rewiring a person," said Kuiken. "The brain doesn't know it's connected to different muscles; it just sends out signals to open and close your hand. We can then use the muscle as a biological amplifier of the nerve signals, picking up that signal and relaying the brain's command to the hand. It's a more natural method of controlling a device."

Unless the nerves are severely damaged, upper-limb amputees are candidates for the process, which also has been applied to transhumeral amputees as well as the shoulder disarticulation subject who has been featured in demonstrations.

Healthy peripheral nerves by their nature want to grow, said Kuiken, "So we transfer the nerves directly onto a muscle they can grow into. In doing so, we're gaming the system by taking a big nerve that has thousands and thousands of nerve fibers and putting it onto a fairly small bit of muscle and skin, so that if only 5 percent or 10 percent of the nerve fibers are successful, that's still more than adequate for our purpose."

Eureka Moments

Kuiken's interest in pursuing nerve transfer research was initiated by a brief reference in a paper he discovered while researching his graduate thesis in biomedical engineering two decades ago. "That idea captivated me; I've been studying it for the last 20 years. There were a lot of things to figure out: How the nerves could grow into the muscles, whether you could sort out all the signals--and the more practical matters of the surgery and the fitting."

It takes from four to six months for nerves to grow into different muscles, so when his research reached the point of applying the nerve transfer process to the first patient, there was a period of suspenseful waiting, followed by a genuine Eureka moment.

Kuiken explained, "We talked to him on the phone about three to four months after his surgery, and he said, I'm getting some twitches in my chest muscle when I try to move my hand.' That was definitely a great moment, and even more so when we brought him in, another month or two later, hooked up his chest muscles, and he made a myoelectric hand close by just thinking about it. THAT was definitely a Eureka moment!"

Kuiken has received considerable acclaim over the last several months since the initial announcement of his success in June 2005. He was recognized as the Grand Award Winner by Popular Science in the 2005 "Best of What's New in Personal Health" category, as well as the daVinci Award, created by the Engineering Society of Detroit and the Multiple Sclerosis Society of Michigan to recognize technology that benefits people with disabilities.

The Potential of Prevention

What if we could eliminate the need for lower-limb prostheses in one entire category of prosthetic patients?

Researchers continue to pursue studies regarding a proposed technique for restoring blood flow and preventing amputation in persons with severe peripheral arterial disease. Findings presented at the Annual Scientific Meeting of the Society of Interventional Radiology (SIR) last spring raise exciting possibilities.

Fatty plaque buildup that clogs arteries can cause decreased blood flow to the legs, resulting in pain when walking, and eventually gangrene and amputation. The condition of tissue loss or resting pain caused by lack of blood is known as chronic critical limb ischemia.

Treating long segments of a blocked artery with subintimal angioplasty, followed by stenting as needed, has been shown to be highly successful in patients with this condition.

David Spinosa, MD, Fairfax Radiology, lead author, explained the value of the study: "It shows that we can treat very severe peripheral arterial disease in the smallest vessels, even those with long lesions, with subintimal angioplasty and stenting, potentially saving these patients from amputation. This finding is significant because patients with severe critical limb ischemia typically have poor wound healing and increased risk of infection following bypass surgery in the leg. Subintimal angioplasty can offer a less invasive treatment.

"The results of this study are particularly exciting because these patients are clinically difficult to treat with angioplasty or surgery, and many go on to amputation," Spinosa said. "Knowing that we can offer potentially successful treatment for these long lesions in patients who typically have few options other than amputation is important."

--Judith Philipps Otto

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What's Next?

Where is his research going from here?

"Now we have to catch up and get the device fitted on more people," Kuiken observed. "We have shown that someone can control six motions; but currently all that is available in the field is a powered elbow, wrist rotator, and hand--three motions. We have to do better in terms of making arms as well as in terms of our surgery before this can become widely available.

"We're hoping to get more research subjects--people who have had above-elbow and shoulder-disarticulation amputations within the last six to12 months to work with and extend the science, and hopefully the broader medical community will want to try it, too. We believe that this technology is very applicable to injured soldiers and hope to be able to help our veterans soon."

Beyond arms, the next "step" may focus on using nerve transfer to provide control of motorized legs, as well as to allow amputees to feel the ground they are walking on. "We hope the whole idea can work with legs as well," Kuiken said, "but that's a ways down the road because we don't have motorized leg parts yet."

Controller: Spinal Cord?

Other researchers have attacked the challenge of re-creating biological movement in prosthetic limbs from a different perspective. Researchers at the McGovern Institute for Brain Research at the Massachusetts Institute of Technology (MIT) are pursuing the theory that it is a series of specialized "command posts" located along the spinal cord that allows humans to effortlessly orchestrate the incredible variety of synchronized motions of which our limbs and digits are capable.

MIT's Emilio Bizzi, one of the principal investigators, believes that the central nervous system "assigns" sets of muscles and the neurons that activate them to a muscle synergy unit.

These muscle synergies relieve our brains of the chore of consciously reviewing each phase of action required by each muscle, in what sequence, and at what relative speed, each time we pick up a pencil or use a set of keys to unlock a door--a process that could take hours if we thought about precisely how our hands, wrists, and arms should move in order to perform each function.

Another study by Bizzi and collaborators, as reported in the Journal of Neuroscience , pursues the influence of sensory input on the spinal cord muscle synergies: By measuring the electrical activity in a frog's hind leg muscles before and after severing the nerve roots feeding sensory information into the spinal cord from the muscles, the team determined that natural jumping and swimming movements seemed unaffected by the lack of input.

The implications of these findings lead researchers to speculate that the future design of neuroprosthetics may be significantly simplified, since only a few signals generated in the central nervous system may be required to control a large number of muscles, due to the near autonomy of the muscle synergy groups.

Definitely a direction worth watching!

Lightweight Hand Includes Opposable Thumb

A recent major fire at the University of Southampton, Hampshire, United Kingdom, has severely affected their work on prosthetics, reported Professor Neil White, School of Electronics & Computer Science at the university. But progress has been made, and will soon continue on the development of a "smart" artificial hand. Paul Chappell, PhD, a medical physicist who designed the prototype, describes the device:

"With this hand you can clutch objects such as a ball, you can move the thumb out to one side and grip objects with the index finger in the way you do when opening a lock with a key, and you can wrap your fingers around an object in what we call the power grip--like the one you use when you hold a hammer or a microphone."

The Southampton Remedi-Hand closely imitates real hand movements by using six sets of motors and gears to move each of the five fingers independently, unlike available prosthetic hands that are either purely cosmetic or offer only a simple single-motor grip.

The Remedi-Hand connects to muscles in the arm via a small processing unit; the hand is controlled by small contractions of the wrist muscles.

The lightweight carbon fiber hand, with its first-ever opposable thumb, weighs 400g--less than the average human hand's 500g. It also incorporates the latest sensor technology, making it "smart" enough to know how tightly it is gripping an object, or whether it needs to strengthen its grip to retain a slipping object before it falls. Piezo-electric sensors in each of the five fingertips detect how much force is being exerted on each fingertip and transmit this information to a processor via electrical signals.

In Other Prosthetic News...

*Ossur's award-winning Rheo Knee™ has established itself as the first artificially intelligent knee system having the ability to learn and adapt to its user's movements in real time, resulting in a continually improved and optimized performance. It has been hailed as the first in a new generation of microprocessor-controlled, swing-and-stance knee systems that incorporate artificial intelligence, giving the system the ability to learn how the user walks and eventually pre-empt each step.

Electronic sensors monitor the knee's activity 1,000 times per second, feeding data to a computer chip that accordingly regulates intensity and causes changes in the magnetorheological (MR) fluid within the knee, improving its responsiveness, the company explains. Ossur noted that the Rheo Knee's DLMA (dynamic learning matrix algorithm) learns its user's movements and quickly adjusts swing and stance resistance to allow the user to walk comfortably and safely at varying rates of speed.

The Rheo Knee's development continues to evolve, while Ossur looks at ways to apply the new technology to other products.

*Coming Soon: Ossur's POWER KNEE™--the world's first powered prosthesis for transfemoral amputees--offers unprecedented functionality, according to Ossur. The company describes the innovative device: "The POWER KNEE replaces true muscle activity , powerfully bending and straightening the knee, and restores gait dynamics while walking on level ground, allowing the patient to cover greater distances with less perceived effort. The POWER KNEE actively lifts the user up the next step, making it possible to ascend stairs and inclines foot over foot. By gathering sensory information one step ahead of the prosthesis, the POWER KNEE anticipates and proactively provides function appropriate to daily activities, such as climbing stairs and inclines. The software can be fine-tuned based on the personal physical condition and rehabilitation level of individual users."

*Coming Soon: "The-soon-to-be-released Freedom Innovations prosthetic knee is a hybrid system combining the industry-preferred features of both hydraulic and microprocessor knees," the company stated. "The electronically controlled stance phase facilitates surefooted gait, while a hydraulic cylinder provides smooth transitions from slow to fast speeds and then back again. The knee's lightweight, slim profile is engineered to increase the scope of amputees that will benefit from Freedom's latest innovation."

Editor's note: This information is for reader information only. The O&P EDGE does not endorse any product or service.

Editor's note: For more information on new prosthetic hand technology, please see The O&P EDGE, November 2005 .

Judith Philipps Otto is a freelance writer who also has assisted with marketing and public relations for various O&P industry clients. She has been a newspaper writer and editor and has won national and international awards as a broadcast writer-producer.