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

A man who had his right arm amputated below the elbow has been able to feel hot and cold in his missing hand via a modified prosthetic arm with thermal sensors.

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

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

“In a previous study, we have shown the existence of these spots in the majority of amputee patients that we have treated,” says Solaiman Shokur at the Swiss Federal Institute of Technology in Lausanne.

First, Shokur and his colleagues mapped the spots 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 can be made hot or cold, called thermodes.

Tests showed that Fidati could identify bottles that were hot, cold or at ambient temperature with 100 per cent accuracy by touching them with his modified prosthetic. When the thermal sensor in the prosthetic was turned off, his accuracy dropped to a third.

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

In a separate study published recently, Shokur and his colleagues showed that people with an amputation using a temperature-sensitive prosthetic can detect whether objects are wet or dry.

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

Omid Kavehei at 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.

“It’s phenomenally important work,” he says. However, he cautions that this wasn’t a clinical trial and wonders how well the technology will work in the real world, where there are vast extremes of warm and cool weather.

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