While most artificial feet and limbs work well to restore mobility to people who have lost a leg, few provide a natural gait. As a result, more than half of all amputees suffer a fall every year, compared to about one-third of people over age 65. To find a better way of restoring natural motion to artificial feet, researchers at Michigan Technological University, Houghton, in cooperation with a Mayo Clinic scientist, are making a bionic foot that could make an amputee's walk feel more like their original foot. They are working on a microprocessor-controlled ankle-foot prosthesis that comes close to achieving the innate range of motion of this highly complex joint.
The computerized artificial legs have pressure-sensitive sensors on the bottom of the foot that detect how the amputee is walking. The sensors instantaneously send signals to a microprocessor, which in turn adjusts the prosthesis to make walking more natural.
The microprocessor-controlled prostheses currently on the market can move an artificial foot toe up and down, which works well on a treadmill. But, they say, most people don’t walk in a straight line for any length of time. They reach obstacles and turn.
So it was important to design an ankle-foot that can move on two axes, incorporating a side-to-side roll as well as raising the toe up and down. And they moved the power and control mechanism up and away from the leg using a cable-driven mechanism. That lightens the prosthesis, making it much more comfortable and easy to use. The cable that moves the prosthetic ankle-foot is similar to those used in bicycle brakes. It runs from the control box to the ankle mechanism and can turn the foot in almost any direction.
As part of their study, the team designed and built a large circular treadmill on which the robotic foot “walks” in circles. In tests, the prosthetic was able to copy the angles of a human ankle walking in a straight line and turning. The researchers will begin refining their design at the Mayo Clinic next summer.
