A novel prosthetic leg with ‘feeling’ improves mobility

AFP, PARIS

Wed, Sep 11, 2019 - Page 6

A breakthrough device unveiled on Monday makes it possible for someone who has had a leg amputated above the knee to “feel” a prosthetic leg, resulting in greater stamina, stability and mobility.

Sensors on a mechanical limb surgically connected to nerve endings in the thighs of two volunteers also reduced or removed the agonizing “phantom limb” pain that bedevils so many amputees, researchers reported in the journal Nature Medicine.

The proof-of-concept study “shows how beneficial it is to the health of leg amputees to have a prosthesis that works with neural implants,” said Swiss Federal Institute of Technology professor Stanisa Raspopovic, who led an international team of 20 researchers.

When an able-bodied person walks or runs, nerves in the feet and legs relay a steady stream of electrical impulses to the brain with real-time data: Is the road uneven, slippery or full of pebbles? Is the surface sloping up or down?

That feedback allows the brain to make instant adjustments to catch a fall or change the amount of force needed.

However, someone with artificial legs does not benefit from that feedback, making it very difficult to walk steadily and with confidence.

“They can’t entirely trust their prosthesis, so they rely too often on their intact leg, which reduces mobility and causes them to tire quickly,” Raspopovic said.

Even a stroll on the beach or on uneven grass can be exhausting.

To restore the flow of signals from limb to brain, the team placed sensors under the soles of the prosthetic foot and around the joint of an electronic knee.

Doctors surgically implanted electrodes into the volunteers’ thighs, hooking them up the same nerve endings that had once sent and received messages from the amputated lower limb.

Once connected by wires that passed through the skin, the sensors and electrodes partially restored the feedback loop.

“We deliver enough sensation to make people much more confident about their prostheses,” Raspopovic said.

Even years after a leg has been removed, “there is accumulated knowledge in the nerve fibers,” he added. “There are enough fibers to elicit sensations through electrical stimulation.”

According to the volunteers, the reduction in pain was striking.

“My big toe, foot, heel, ankle, calf — they all hurt and I don’t even have them,” Savo Panic said, adding that the pain is strong enough to wake him up at night.

“Since I have started the treatment, I don’t feel any phantom pain,” Panic said.

Working with technology firm SensArs, the researchers plan to carry out large-scale clinical trials within the next four years.