Sensitive prosthetic lets man feel hot and cold in his missing hand

Fabrizio Fidati tests temperature-sensitive prosthetic arm

EPFL Caillet

A man with a right arm amputated below the elbow was able to feel hot and cold in his missing hand thanks to a modified prosthetic arm with thermal sensors.

After an amputation, some people may still experience sensations of touch and pain in their missing arm or leg, called a phantom limb. Sometimes these sensations can be triggered by nerve endings in the residual upper limb.

The prosthesis works by applying heat or cold to the skin of the upper arm at specific locations that trigger a thermal sensation in the phantom hand.

“In a previous study, we showed the existence of these spots in the majority of amputee patients that we treated,” explains Solaiman Shokur at the Ecole Polytechnique Fédérale de Lausanne.

First, Shokur and his colleagues mapped the points on study participant Fabrizio Fidati's upper arm that trigger sensations in different parts of his phantom hand. Then they adapted his existing prosthetic hand and socket with sensors and devices that could be made hot or cold, called thermodes.

Tests showed that Fidati could identify hot, cold or room temperature bottles with 100% accuracy by touching them with his modified prosthetic. When the prosthesis' thermal sensor was turned off, its accuracy dropped to a third.

The prosthesis also allowed Fidati to successfully, blindfolded, distinguish glass, copper and plastic by touch with an accuracy of just over two-thirds – the same as that of his uninjured left hand.

In a separate study published recently, Shokur and colleagues showed that amputees using a temperature-sensitive prosthesis can detect whether objects are wet or dry.

“We could provide a sense of moisture to the amputees and… they were as good at detecting different levels of moisture as with their intact hands,” Shokur says.

Omid Kavehei from the University of Sydney, Australia, says the research could one day have applications beyond prosthetics, such as giving robots a greater range of physical sensations.

“This is phenomenally important work,” he says. However, he cautions that this is not a clinical trial and questions how well the technology will work in the real world, where temperature extremes are hot and cold.

“I would like to see how this device performs in a hot and humid place like Singapore,” says Kavehei.

The subjects:

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