CPU-controlled artificial leg offers new freedom of natural movement for amputees
By Loz Blain
July 26, 2007
July 27, 2007 Prosthetics is a fascinating field – science’s ability to mimic the complicated natural function of lost limbs can make a truly life-altering difference for amputees. Nowhere is this difference more strongly felt than in the field of artificial legs that get amputees out of wheelchairs, off crutches and back to a level of mobility that lets them blend back in into ordinary life. The latest drive towards the development of advanced prosthetics includes this new microchip-controlled artificial knee joint that’s opening up an unprecedented level of freedom of movement for above-knee amputees and allowing amputee servicemen to remain active in their jobs if they so choose. The US$30K hydraulic C-LEG’s CPU “brain” automatically adapts to changes of speed and direction, and can be pre-programmed into up to 10 switchable “modes” to enable natural driving, cycling and other programmable activities that require different leg actions to normal walking and stair climbing.
In 2006, Otto Bock HealthCare, a global provider of prosthetic components that started out providing devices for German World War I veterans in 1919, began developing a prosthetic knee system as an upgrade to its already popular C-Leg. It was awarded a three-year $1 million contract to develop a leg that will allow more US Army service members to stay on active duty if they choose to.
The prosthesis is for above-the-knee amputees and uses a microprocessor to interpret the wearer’s movements and anticipate their actions, making motion changes in real time. This smart system, actuated through the leg’s hydraulic movement capabilities, will give wearers greater flexibility to change speeds or directions without sacrificing stability, making for a much more natural experience that requires minimum concentration.
Mobility will be improved, allowing more movement without the user having to concentrate on the knee, said program manager Hans-Willem van Vliet. The new system will have more sensors, a faster hard drive, more memory, and will provide smooth automatic transitions between common movements such as level-ground walking, climbing stairs and running.
It also will give wearers the ability to turn around while walking, or walk backward in one fluid movement, something that is not possible with the current C-LEG. It will adapt automatically between walking speeds and gaits, Mr. Vliet said.
Engineers are working to stretch the unit’s battery life to 50 hours on one charge to support wearers in the military. This will give service members on long road marches the duration they need to reach a power supply for recharging. Requirements also call for making the system salt-water resistant in order to overcome problems associated with the onboard computer systems.
The current C-Leg allows wearers a choice between two operating modes: one for walking and one for bicycling or another pre-programmed activity. To switch between modes, the wearer has to swing the leg forward in a jerky fashion. The new unit will support up to 10 programmable modes, switchable through a small remote control about the size of a car alarm remote. Reprogramming a mode will require a visit to a technician, as is currently the case.
Lt. Col. Andrew Lourake, a pilot at Andrews Air Force Base, Md., is the first above-the-knee amputee to return to active duty as a pilot. He was fitted with a C-Leg five years ago. Lt. Col. Lourake said he could not do his job without the C-Leg because it allows him to switch between walking and flying modes. Still, he said, he is impressed with the new design and plans to be one of the first to own one, even if he has to pay for it out of his own pocket. The current C-Leg costs about $30,000. The new system is expected to cost about the same.
"I'm excited. It has a lot of the stuff that I asked for a couple of years ago. It's huge in functionality and active living," Lt. Col. Lourake said.
Right now, he has to reprogram his second mode from flying mode to bicycling or running. With the new leg, he won't have to make as many visits to his prosthetic technician. "I'll have everything right in the leg, and I'll never have to touch the computer again," he said.
The project began in 2006, and is currently in the prototype stage. Barring any technical problems, the new prosthesis should be available to service members in 2009.