April 2006

The Stuff of Dreams

By Stephen Krcmar

Prosthetics are quickly evolving beyond functional into fantastic.

Jay Martin, CP, LP, tests a prosthetic hip socket.

The year 2005 was groundbreaking for the prosthetics arena. When the "bionic" arm was developed by physiatrist Todd Kuiken, MD, PhD, of the Rehabilitation Institute of Chicago (RIC), it captured the eye of the popular media and offered a glimpse of the future. Mainstream interest was piqued because the 12-pound arm marked the entry of prosthetics into a realm that was formerly relegated to science fiction: The wearer only has to think about a particular motion, like picking up a paintbrush, before the artificial limb responds accordingly.

BELOW THE BELT
Breakthroughs were not limited to advancements that took place above the belt. The first motorized knee prosthesis gives leg amputees fluid motion by simulating the movement of the real knee next to it. The motorized knee prosthesis uses artificial intelligence to predict and respond to changes in terrain and incline. Like a good spouse, the motorized knee prosthesis is successful because it listens to its other half—the natural leg is outfitted with sensors that take 1,350 measurements per second and wirelessly transmits the information to the artificial limb. The 10-pound motorized knee prosthesis processes the information concerning the neighboring leg, and a brushless motor drives the device toward a goal of balanced gait. For the first time in history, amputees saw a product that would enable them to ascend stairs and ramps while facing forward.

"This is a very exciting time for us and a very exciting time for the field as a whole," says Jay Martin, CP, LP, director of research and development at a prosthetics and research company in Oklahoma City. "There are a lot of exciting things coming down the pipe. What we're going to see in the next couple of years in the field will completely revolutionize the technology that's available."

Last year, Martin's company released a new socket design specifically developed for the hip-disarticulation or hemipelvectomy amputee. It was a long time coming for many. Martin says the socket technology had not changed much in the past 2 decades and the old systems were often bulky, heavy, and uncomfortable. To further complicate matters, older hip level sockets are difficult to use because the high-level amputation controls all three joints of the leg. The old design does not lend itself to precise movements. Since the socket is the interface between the body and the prosthesis, the functionality of the artificial limb is limited by the quality of socket: like high-performance tires on a car that has substantial play in the steering, even good prosthetics suffered from low-tech sockets.

The first patient fitted with the new socket was a ferryboat captain, who was very active, but was dependent on crutches for 18 years. The first time he was outfitted with the new socket design, he dropped the walking aids immediately and walked across the room.

The new system fits the contours of the pelvis and optimizes control and comfort. Because the unit is smaller, it is more discreet than previous designs. Researchers at Martin's company are also busy developing sockets for upper extremity amputations.

Socket developments are not the only thing the researchers have up their sleeve. "In recent years, we've seen some of the Model T [Fords] of lower extremity prosthetics, like the [microprocessor-controlled hydraulic knee with swing and stance phase control]. But we're taking some of that technology to the next level using artificial intelligence control and enabling the prosthesis to, in essence, think and respond and react to the environmental changes," says Martin.

COMPUTER-CONTROLLED DESIGNS
According to Martin, there are a number of projects in production that are built around computer-controlled designs. "Our bodies are not just mechanical," says Martin, "but historically prosthetics have been mechanically based due to limits in technology." New innovations will attempt to simulate the body's electrochemical communication: receiving information from the outside world, translating it, and communicating the next movement to appendages. For example, when walking, the mind considers the terrain, the speed of locomotion, how much force is on the limb, and whether a load is being carried. Now, computers can take in many of these factors and interpret them, much the same way the brain would. After interpreting the data, the computer can send necessary instructions to the prosthetic.

"The control feedback loop of the human body is very complex. To mimic that in a computer system in a manner that provides full, appropriate, biomechanical movement independent of changes in the environment is not an easy task," says Martin. "But, so far, we have been able to demonstrate some very positive results with our development efforts."

Multiple companies in the world of prosthetics are studying these cerebral projections and the difference comes down to the approach.

Jay Martin, CP, LP, left, and Scott Sabolich, CP, LP, discuss a prototype of a new computerized prosthetic ankle joint.

Currently, researchers at Martin's company are at work on computer-controlled ankle joints, and plan on translating their knowledge into a knee joint in the near future—with plans to make it to the marketplace within 3 years.

"In designing this next generation of prosthetics, it's a whole different world than designing the old-styled mechanical systems or the basic electronic systems that are used today. We've run across a lot more challenges and we're kind of diving into an arena that is really brand-new; there's not a known skill set or methodology—there's nothing to compare it to. There are a number of challenges to bring it to fruition," Martin says.

FINE-TUNING PROSTHETICS
In the meantime, physicians and researchers at RIC are taking a different approach: They are concentrating on fine-tuning different ways to control the prosthesis. They have teamed with Richard Weir, PhD, at Northwestern University who is developing an intramuscular electrical sensor (IMES). Basically, it takes advantage of an injectable RF-powered, single-channel ceramic-cased microstimulator that can be implanted via a novel trocar-based implant tool or via surgical opening, near a nerve or into a muscle. The technology usually is used for the stimulation of muscles. Weir has modified technology so that it can also receive information, according to Laura Miller, PhD, staff prosthetist at RIC.

For example, the forearm controls many of the motions of fingers. When there is an amputation, it is difficult to get all the signals for smaller movements like finger motion. With the new technology he is working on, Weir hopes that small electrodes that are implanted in the forearm will be able to control a sophisticated mechanical hand. One problem: the hand does not exist.

"It's a catch-22: no one has developed the hand because there is no way to control it," says Miller. "Potentially, by having a way to control [the hand and fingers], someone might develop it. [Researchers are working to] develop hands with more function."

Miller believes that prosthetics will be more functional in the future. Hands will be able to do more than just open and close. They will be able to move in different ways. For higher level amputees, shoulder movement is going to be critical for prosthetic development. Lastly, the question of battery power also could be a limiting factor.

"It seems like a silly thing, but it does have an impact on how many things we can control and how much power they can have, based on how often they have to plug themselves into the wall," says Miller, speaking about the lithium ion and lithium polymer batteries that are part of the units.

PROSTHETIC AESTHETICS
Beyond control issues, many amputees put high value on having a prosthetic that looks natural. Prosthetist Jackie Fancher's Dallas-based prosthetics company has been focusing on the aesthetics of silicone prosthetics since 1980. "Paint on hands and fingers lasts about 5 years," says Fancher, executive director of the company. "Paint on feet lasts longer—often more than a decade—because it is protected for most of the day by a sock and a shoe." Technicians at Fancher's company create and hand-paint silicone and myoelectric prosthetics, matching every lifelike detail to their client's specifications—including hair, freckles, veins, and nails. Although the technique used by her company is a trade secret, Fancher impresses that advances in paint and material technology have benefited the look of the devices. Nonetheless, Fancher recommends annual maintenance for prosthetics owners.

Stephen Krcmar is associate editor of Rehab Management.

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