A prosthetic leg that attaches to nerves feels like part of the body

Prosthetic legs with sensors can help people avoid unseen obstacles underfoot. Three people who have had a leg amputated found that they perceived such prostheses as an extension of their own body and were able to climb stairs more quickly than they could with a conventional prosthetic leg.

Prosthetic limbs are often abandoned due to people’s poor mobility when using them. The devices don’t restore sensation, leaving people to rely on touch feedback from the stump meeting the socket.

Stanisa Raspopovic at the Swiss Federal Institute of Technology in Zurich and his colleagues modified a commercially available prosthetic leg by adding sensors to an insole on the foot and inside the knee. Electrical signals from these regions were then delivered through tiny electrodes implanted into nerves in the participant’s thigh.

When the foot touches the ground or when the knee bends, those nerves carry signals to the brain and allow the individual to more quickly and precisely adjust how they are walking.

The team recently found that this prosthetic leg helped two people feel less fatigue and phantom limb pain and helped them to navigate an outdoor track more quickly than when the sensors weren’t on.

In this study, Raspopovic’s team found that blindfolded participants could tell which part of their foot was being touched about 90 per cent of the time.

Then the participants tried the legs while climbing stairs and walking over obstacles that they couldn’t see. These tasks are extremely difficult for people wearing traditional prostheses, says Raspopovic.

Participants were able to walk up and down stairs an average of 30 per cent faster when the sensory input was turned on. Similarly, they were up to seven times more likely to fall over an unseen object without input from the sensors.

The technology behind prosthetic limbs has been advancing rapidly in recently years. Different types of controllable prostheses convert electrical signals from the brain or body into movements in the device, which is especially useful in controlling the fine movements of the hand.

One UK group has developed a bionic hand that uses artificial intelligence to automatically grab objects, speeding up the time it takes to learn how to control these artificial limbs.