Prosthetic leg sensitivity triggers feeling of hot and cold in amputated hand

A man who had his right arm amputated below the elbow can now feel heat and cold in his missing hand through an improved prosthetic hand equipped with a heat sensor.

After amputation, some people may still have a sense of touch or pain in the missing arm or leg, known as a phantom limb. In some cases, these sensations may be caused by nerve endings in the remaining upper limbs.

This prosthetic hand works by applying heat or cold to specific areas of the skin on the upper arm, inducing a thermal sensation in the phantom hand.

“Previous studies have shown that these spots are present in the majority of amputee patients we treat,” he says. Solaiman Shokur at the Swiss Federal Institute of Technology in Lausanne.

First, Shokur and his colleagues mapped spots on study participant Fabrizio Fidati's upper arm that triggered sensations in different parts of the phantom hand. They then outfitted his existing prosthetic arm and socket with a sensor and device called a thermodes that can make it hot or cold.

Tests showed that Fidati was able to identify hot, cold, or ambient temperature bottles with 100% accuracy by touching the bottle with the modified prosthesis. When the thermal sensors in his prosthetic limbs went off, his accuracy dropped to a third of his.

The prosthetic hand also allowed Fidati to distinguish between glass, copper, and plastic by touch, while blindfolded, with just over two-thirds of the accuracy of his uninjured left hand.

In another recently published study, Shokur and his colleagues showed that amputees use temperature-sensitive prostheses. Can detect whether an object is wet or dry.

“We were able to give amputees the sensation of moisture, and they were able to detect different levels of moisture, just like a healthy hand,” Shokul says.

Omid Kabehei Researchers at Australia's University of Sydney say their work could one day have applications beyond prosthetic limbs, such as giving robots a wider range of bodily sensations.

“This is very important work,” he says. But he cautions that this is not a clinical trial and questions how well the technology will work in the real world, where warm and cold climates are extremely different.

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