Science Quickens Its Steps
In the history of war, the more proficient combatants have become at fighting, the better medicine has become at healing.
During World War II, battlefield doctors devised better techniques to repair delicate blood vessels, essentially rewriting the textbooks on vascular surgery. The Vietnam War sparked swift helicopter evacuation of the wounded that was soon copied by urban medical centers throughout the United States.
For the wars in Iraq and Afghanistan, the medical legacy will probably belong to the amputee. The rate of amputation injuries among U.S. troops in these conflicts is almost twice as high as in any previous American military conflict, because of insurgents’ predominant use of explosives. Some troops who would have died in past wars are being saved by body armor, which doesn’t protect arms and legs.
Government agencies, private companies and independent researchers are creating more high-tech prosthetic limbs in response. In doing so, they’re pushing the boundaries of what researchers and doctors once thought possible.
“Never has there been a time, in my experience, where the amputee has been offered so much to overcome the obstacles of having to adjust to their new body,” said Robert S. Gailey Jr., assistant professor of physical therapy at the University of Miami and a longtime prosthetics researcher. “These young men and women will never understand what those who lost a limb 25 years ago had to go through.”
Unlike the dead-weighted and immutable arms, feet and knees offered to veterans of the Vietnam War, the best prosthetic knees currently available rely on artificial intelligence to anticipate the user’s movements. One knee, expected to become available in a few months, will even mimic lost muscle activity by powering ankle and leg amputees up stairs, or up from a sitting position.
But that’s just the beginning. Advances in robotics, electronics and tissue engineering ultimately could create ways to lengthen damaged limbs, grow new cartilage, skin and bone, and permanently affix a prosthesis to the body. Some researchers are even designing a so-called biohybrid limb -- a prosthesis that can be controlled by the user’s thoughts.
The biohybrid limb is designed to reduce the amount of effort needed to move the limb and thus limit falls, increase feelings of security and improve self-image. The user of such a leg could spring from the sofa to catch a baby who is about to tumble from a highchair.
In short, researchers predict, it would be as good as a natural human limb
“A decade or two ago we imagined a neural interface, but it was science fiction,” said Hugh Herr, a researcher at the Massachusetts Institute of Technology who lost his feet at age 17 to frostbite during mountain climbing. “But now these things are pretty close to being realized in the laboratory.”
The advancements resulting from the latest American wars are defined largely by the fact that battle injuries have changed -- as have the soldiers.
Only 10% of the U.S. casualties in Iraq have been deaths, compared with 30% in World War II and 24% in Vietnam, according to a 2004 study in the New England Journal of Medicine.
But 6% of the wounded have required amputations, compared with 3% in past wars, according to a U.S. Senate report. As of last March, the most recent data available, 428 amputations were reported from U.S. troops in Iraq.
Meanwhile, the current generation of GI amputees is the most athletic of any American war, doctors say, with high expectations for their recovery. Some are remaining as active-duty troops, and at least one foot amputee has returned to action in Iraq.
“They want prosthetics that return them to high levels of function,” said Robert Ruff, a neurologist and acting director of rehabilitation research for the Department of Veterans Affairs. “The soldiers are in excellent cardiovascular shape, so they place more demand on the prostheses.”
And for troops to recover, physically and psychologically, from amputations, they need hope and the best that technology has to offer.
Chang Wong, 23, of Alhambra was a high school wrestler who prided himself on his fitness, before he lost both legs just below the knees while serving in Iraq. Now he’s using his former image of himself to boost his recovery, recently learning to run on his prostheses.
On a day in late December he sat on the curb of the track inside a health club in Rosemead and popped on his running feet: high-tech titanium and carbon fiber appendages that looked a little like curved skis with thick rubber soles of running shoes glued to the bottoms. He stood up with a bounce -- the prosthetic running feet provide so much flexibility that Wong springs slightly when he walks. He headed down the track and out of sight, steady and quick as the next guy.
He’s come a long way. Last May, the tank in which Wong was riding struck an improvised explosive device buried in a dirt road outside Baghdad. Wong, in the gunner’s seat on the floor, bore the brunt of the explosion.
“I knew I had to get out of the tank,” said Wong, a thin, soft-spoken man who joined the Army with a group of friends in 2001. “But when I tried to stand, I couldn’t. I looked down and saw that my legs were smashed.”
When he finally became fully conscious almost a month later, he was lying in Brooke Army Medical Center in San Antonio, envisioning a life reliant on a wheelchair.
Wong’s caregivers at Brooke coaxed him onto prosthetic feet when he was still unsure whether he wanted to live. After taking his first steps, he decided “there was no point in looking back. Now I hold my head high and encourage other people.”
His short-term goal is to increase his lung capacity so he can run farther. Long term, he’d like to return to school and earn a degree in physical therapy so he can help fellow amputees. Although Wong has several high-tech prostheses that allow him to walk, run and swim, he’s keeping an eye out for improvements.
The next big thing in prosthetics will be powered devices, which are expected to reach the market soon. The Rheo knee -- which uses artificial intelligence, in effect mimicking the ability to think -- is considered the most sophisticated prosthetic limb available.
The Rheo, which hardly resembles a real limb, consists largely of a thick rod of titanium and a brick-size blue box covering a microprocessor. It doesn’t have a motor, but is gait-adaptive, adjusting automatically to what the user desires at any given moment. Electronic sensors monitor the angle and load borne by the knee joint at a rate of 1,000 times per second while a special fluid passing through a magnetic field changes viscosity, or friction, to allow the user to move or brake efficiently. A computer chip creates and regulates the intensity of the magnetic field to facilitate movement.
“It appreciates what you’re trying to do and adjusts to that,” said Hilmar Janusson, vice president of research and development for the Iceland-based prosthetics company Ossur, which invented the Rheo knee. “It’s like if you had one gear in the car and you had to stick to that whether you were going uphill, downhill or on a freeway. Now you have a gear box and a control mechanism that selects the gear for you.”
Like many amputees who seek out the newest, best devices, Mike McNaughton recently requested -- and received -- a Rheo knee from the VA.
The 34-year-old was clearing land mines as a National Guard sergeant in Afghanistan in 2002 when he stepped on one and lost his right leg. At the time, he expected to receive a limb made of wood. “I didn’t know anything about prosthetics,” he said.
McNaughton quickly adapted to a C-Leg, which was introduced in 1999 as having the first microprocessor-controlled knee that could be programmed to the user’s movements.
He then sought a Rheo knee. “It keeps up with you,” said McNaughton, who is now employed by the Department of Homeland Security in Louisiana to help with the Hurricane Katrina recovery effort. As a resource manager for the department, McNaughton orders cots, food, generators and other supplies to support those rebuilding in the storm region.
“If you walk fast, it walks fast. I played with my son during his soccer practice the other day. I hung in there with the kids for a while,” he said.
But the most highly anticipated advance in the new generation of artificial limbs may be Ossur’s Power Knee, expected to become available in a few months. This knee utilizes artificial intelligence, but it also has a motor to provide missing muscle power. It might be best suited for amputees who have trouble walking distances or navigating stairs or inclines.
The Power Knee gathers information one step ahead of the prosthesis. Sensor equipment positioned on the sound foot measures motion, load and the position of the natural limb at a rate of about 1,350 times per second. The information is then transmitted to the artificial knee, which calculates the precise amount of power needed.
Troops returning from war are ideal candidates to receive the latest technology in prosthetics, experts say.
They “are making these really incredible sacrifices. I think, quite properly, society feels we owe them whatever we can give them,” said Dr. Roy Aaron, who is heading a VA-funded biohybrid limb research team at Brown University in Providence, R.I.
The next big leaps in prosthesis technology will probably require researchers to better use whatever human tissue remains, and access the body’s most powerful tool, the brain.
Aaron is studying whether it’s possible to grow cells for bones, skin, muscle and cartilage and then inject the result into damaged joints to increase function.
Growing cartilage and muscle is proving harder than regenerating bones and skin. But researchers have made progress in encapsulating key cartilage growth factors in tiny particles called biodegradable polymer beads. The particles are then injected, spurring the formation of new tissue.
Other researchers hope to make better use of mangled or amputated limbs through a process called limb lengthening. For decades, doctors have added several inches of height in children with dwarfism or other physical deformities by threading wires through the skin and bone in legs and linking the wires to a frame outside the limb. Over a period of months, subtle adjustments to the wires stretch the bone, and new bone grows to fill in gaps.
The same treatment -- if it can be shown to work in adults -- could help resolve a major problem in prosthetics today. When a limb is amputated just below the joint, not enough of the limb remains to securely attach a prosthesis. Lengthening the remaining bone even a few inches would provide a firmer coupling for artificial knees, ankles or arms, Aaron said.
Most prostheses attach to joints with cuffs that adhere by suction, leaving the skin to absorb much of the stress and strain of movement. Studies underway at Brown and elsewhere aim to permanently join a prosthesis to the bone using a titanium implant.
For the process, called osseo-integration, to be successful, however, scientists will have to find a way to prevent bacteria from entering the body where the bolt for the prosthesis protrudes through the skin. The goal is to find a titanium alloy that is strong enough and yet porous enough for cells to adhere to it, forming a tight seal.
“If they can make the prosthesis part of the bone, and make sure it is not going to be infected, it will be wonderful because it will be weight-bearing,” said Paddy Rossbach, president of the Amputee Coalition of America, a nonprofit educational organization based in Knoxville, Tenn. “It’s just like teeth implants. You put a pin into the bone. But with a limb prosthesis, the pin has to come out through the skin.”
The ultimate goal of biohybrid limbs, however, lies in neuroprosthetics -- the ability to control an artificial limb using thoughts. This technology works by capturing brain signals, or nerve impulses from the residual limb, and translating those into computer commands that tell the prosthesis what to do: lift, move left or right, speed up, stop.
In his MIT lab, Herr is inserting a Bion, a microchip about the size of a grain of rice, into existing leg muscle where it can pick up signals from nerves and send movement instructions to the prosthesis. Sensors on the heel and foot of the prosthesis relay information back to the microprocessor to guide movement.
The first studies on prototype devices are underway.
“The goal of these systems is to be completely seamless and natural, like your own limb,” Herr said. “If the amputee has to think about it and struggle, it won’t work. They’ll throw it away.”
At a Foxborough, Mass., company called Cyberkinetics Neurotechnology Systems Inc., a system called BrainGate may someday be used to help amputees operate a smart prosthesis. The system decodes brain waves -- thoughts -- and translates them to computer commands. Preliminary studies have shown that a quadriplegic can switch on lights and move a computer cursor with thought alone. A small chip is implanted in the primary motor cortex of the brain. Signals gathered by the sensor travel through wires to a metal pedestal implanted in the skull and out of the body through a cable. The data are digitized by a processor and decoded into movement commands.
The goal is to design a wireless, implanted system, said John Donaghue, who leads the scientific development team.
“The challenge for making a good interface with biological tissue is making it miniature,” said Donaghue, chairman of the department of neuroscience at Brown. “I am completely confident there will be such a technology.”
People who have lost arms stand to benefit the most from neuroprosthetics. Advances in prosthetic arms have lagged behind knees and ankles because of the intricacy required to move elbow, wrist and multiple finger joints. The best artificial foot-ankle system today provides a user with about 50% to 60% of normal function; knees, about 30%; and arm-hand systems, only about 5%, said Ossur’s Janusson.
In research at the Rehabilitation Institute of Chicago, Dr. Todd Kuiken has transferred four nerves from the shoulder of a man who lost both arms in an electrical accident into pectoral muscles in his chest. The nerves that had once controlled the man’s arms are able to detect signals from the brain from electrodes placed on the chest. After attaching a prosthesis, the man can open the hand simply by thinking about it.
“The neuroprosthetics behave like something you’ve seen in ‘Star Wars,’ ” said the University of Miami’s Gailey. “You think about it, and the mechanical appliance responds. That is the ultimate goal.”
All of the designs for future high-tech prosthetics face challenges. The microprocessor-driven devices need to be smaller, quieter and require charging only once a day, Herr said. They need to better mimic natural speed and energy output, something Herr thinks can be corrected within a decade. Helping leg amputees achieve natural balance will be harder. And the ability to feel one’s surroundings with a prosthesis is a huge hurdle.
“The movement aspect is a bit easier. The hard thing is getting sensation,” Brown University’s Aaron said.
But even today, advanced prosthetics, combined with a rigorous rehabilitation program, are leading to quicker and more satisfying recoveries for amputees, experts say.
Amputee rehabilitation at Brooke Army Medical Center includes Friday night outings to bowl or play laser tag or paintball. “It gets you used to the fact that people stare at you,” Wong said of the excursions.
Amputees seem to care little that the latest prosthetics look nothing like a limb.
“When a prosthesis does not work very well, often the psychological reaction of the amputee is to make every attempt to make the prosthesis look human. They are ashamed of it,” Herr said. “But when the device works, often amputees do the opposite. They expose the fact that it doesn’t look like a human limb. They think it’s cool.”
At Ossur, North American division President Eythor Bender envisions a prosthesis that is both so high-tech and realistic-looking that users could wiggle their artificial toes.
“That’s something we take for granted, but amputees still have this device on their leg,” Bender said. “God did a really good job. It’s difficult to imitate it.”