Artificial limbs that walk naturally
March 2, 2006 German scientists have developed a new type of prosthetic foot that imitates the natural walking motion so convincingly that you have to take a second look to realize its user is wearing a prosthesis. The foot is purely mechanical and entirely without elaborate electronics.
Every year, tens of thousands of people in Germany alone have to learn to walk again because they have lost limbs as a result of disease, accidents or acts of violence, and are now obliged to use prostheses. According to statistics compiled by Germany's largest health insurance provider, AOK, approximately 44,000 toes, feet, lower legs or whole legs were amputated in 2001.
"And the numbers are likely to increase," believes Dr. med. Urs Schneider of the Fraunhofer Technology Development Group TEG, Stuttgart. "Most amputations today are the result of diabetes or peripheral arterial disease – and statistically speaking, the risk of contracting these diseases increases with age.
Older people in particular need artificial limbs that will enable them to walk without having to re-learn too much." But this has been the very problem so far, even though the simple wooden leg is now a thing of the past. Modern leg prostheses can do far more than merely support their wearers. Today's orthopedic technicians can choose from an awesome array of standardized modules to build artificial limbs that are not only tailor-made for their wearers, but in extreme cases may even enable them to pursue serious sports.
A key element of any leg prosthesis is the prosthetic foot. Some models currently available are capable of rotating around three axes and accommodating to uneven terrain. "However, no prosthetic foot has yet been produced that can imitate the natural sequence of movements during walking," Schneider points out.
He and his team have developed a prosthetic foot that can do this – by purely mechanical means, entirely without elaborate electronics. A human foot performs a tiny and almost imperceptible rotation with every step that it takes. After the heel strikes the ground, the foot first tilts inward and then rotates across its central position to the outer edge as the weight is transferred to the ball of the foot, while the hip pushes forward in preparation for the next step.
The prosthetic foot created by Fraunhofer TEG, for which a patent is pending, imitates precisely this rotating motion. By imitating the natural sequence of movements during walking, it not only saves fresh amputees the laborious process of learning to walk again – it is also kinder on the intact knee and hip joints and the lumbar portion of the spine. "Clinical trials have shown that because of the natural-looking gait, hardly anyone notices that the person is wearing an artificial limb," says Schneider in summary.
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