Waiting For an Arm and a Leg

Prosthetics´ Manhattan Project

Nothing about a prosthetics patient´s fake limbs is optimal-not their speed, mobility, comfort or looks. This is partially because the market, though steady, is small, and the funding to advance prosthetics technology doesn´t flow as heavily as it does in, say, cancer research. There are about 1.8 million amputees in the U.S-mostly elderly stroke and diabetes patients-but the number of prosthetics users is significantly lower. Another inhibiting factor, of course, is the tremendous challenge of mechanically replicating the movement and dexterity of human limbs, which are as dependent on two-way communication with the brain as they are on the strength of bone and muscle.

But Halfaker and Stockwell were injured at an auspicious moment in the country´s attitude toward the prevention and treatment of limb loss. The nationwide support organization Disabled American Veterans has been lobbying for improved care for aging veterans hobbled by back and hip pain aggravated by poor-fitting prosthetics. Meanwhile, in Iraq, Kevlar vests and slick battlefield surgical units have kept more wounded soldiers alive (even if with missing limbs) than during any previous war. Government officials, keenly aware of the shoddy treatment given injured Vietnam vets-who often waited months for prosthetics-have vowed that these young men and women would not be treated the same.

In addition to the best care available now, that promise has sparked serious investment in the future. Don´t just think sockets and computerized body extensions, scientists are being told. Collaborate across fields. Explore every angle-even the regenerative powers of salamanders [see "Salamander Secrets," page 74]. In 2005 the Department of Veterans Affairs budgeted $7.2 million to create the Center for Restorative and Regenerative Medicine at the VA Medical Center in Providence, Rhode Island. This year the Defense Advanced Research Projects Agency-which has paid for everything from mine-hunting robotic lobsters to sleep-deprivation research-began funding two prosthetics projects for $48.5 million, hoping the teams will devise a stronger, more functional arm in two years and, in four years, a neurally-controlled arm with sensory capabilities and greater degrees of motion.

The ultimate goal: to create prosthetics that interact with the body, tapping directly into the brain´s desires and sending back progress reports. To do this, artificial limbs will need additional sensors to gather information on speed, angle, gait and balance. Improvements in metals, plastics and other materials will make prosthetics lighter, more flexible and more easily integrated onto the body. "It requires a kind of Manhattan Project" in terms of coordination and commitment, says prosthetics innovator Hugh Herr, director of the biomechatronics group at MIT´s Media Laboratory. Herr is a uniquely knowledgeable advocate for amputees, having worn two below-the-knee prosthetics for decades, since losing his legs to frostbite while ice climbing in New Hampshire as a teenager. "We're at a time in history where there are many core technologies that are getting close," he says. "And if there's funding, there will be an opportunity for dramatic and profound innovation-what even Hollywood would view as bionics."

Painstaking Progress

Before World War II, amputees wore static prosthetic attachments that were little better than peg legs. Then came complicated strap-, cable- and pulley-intensive mechanical arms, which opened a claw. By the 1960s, Soviet scientists had discovered that the amputee´s body has far more resources to call upon. Electrodes placed on the skin could detect a muscle´s myoelectric signals-its contractions-and transmit them to a battery-powered prosthetic, which would bend or straighten the arm. By the early 1980s, as the needs of injured Vietnam veterans spurred research, microprocessors allowed for gradations of movement and speed, rotation and flexion. Still, the stiff prosthetics make a series of many individual, sometimes jerky motions instead of executing seamlessly combined moves. The technology has advanced past the old myoelectric arms, which processed one signal at a time to move the elbow, wrist or hand. But even with simultaneous functioning of these controls, motions can be slow and require the wearer´s intense concentration. Simply doing dishes or getting dressed can be exhausting.

Prosthetic-leg wearers have seen more innovation than those needing arms, partly because there are more lower-limb amputations (95 percent of amputees), which means a bigger market for those working to improve the technology. Stockwell's C-Leg, made by Otto Bock HealthCare in Germany, employs a microprocessor and hydraulics to enable the leg to swing forward automatically once a certain percentage of the wearer´s weight has shifted. The Icelandic company Ossur´s newer Rheo knee is similar to the C-leg, using a microprocessor to sense the knee´s position and load, which allows the leg to adapt to the person´s gait.