The kinds of prosthetic limbs available to leg amputees are far from perfect. They come with a risk of falling, decreased mobility, and don’t feel like a true extension of the leg. These factors, along with the accompanying mental burden, lead to many people abandoning their prostheses altogether. But a new creation could change that.

Reporting their findings in Science Translational Medicine, researchers have tested a new prosthesis on three above-knee leg amputees. Dubbed a neuroprosthesis, the device stimulates nerves in the leg, which in turn helps the wearer to feel when the knee or foot is being touched. This allows for better detection of objects that might trip you up and creates the feeling that the prosthesis is truly a part of the body. Currently available prostheses rely only on sensation where the artificial limb meets the body.

The new device is built on a commercially available lower leg prosthesis but has added sensors in the knee and sole of the foot which create the sensations of balance and pressure, which can then be transferred to the nerves via tiny electrodes surgically implanted in the leg. It was first tested out on two amputees who found it allowed them to walk much more easily and reduced their phantom limb pain. This proof-of-concept study was published in Nature Medicine last month.

In the newer study, three participants tried out the prosthesis and became more adept at activities such as walking up stairs and navigating an obstacle course when equipped with their new limb. Meanwhile, they were better at determining when their artificial leg was being touched, even when blindfolded and deafened with earplugs.

In addition to these physical improvements, the amputees also fared better psychologically. They felt a greater sense of ownership of their prosthesis as it felt more like a part of their body, and were less worried about their leg when partaking in activities.

Overall, the participants were more agile, mobile, and less likely to fall over when they encountered an object they hadn’t spotted with their eyes. They could climb stairs almost a third faster than they would otherwise and were more relaxed when using their prosthesis.

So what are the next steps?

"We aim for an investigation longer than three months, with more subjects, and with in-home assessments," Professor Stanisa Raspopovic, of the Institute of Robotics and Intelligent Systems at ETH Zurich, told IFLScience. "It should be executed to provide more robust data to draw clinically significant conclusions about the improvement of the health and quality of life of patients. To do so, we will work to construct the fully implantable system, which would need collaboration with a company able to provide us with the implantable pulse generator (IPG), which can be controlled, through the skin, with minimal delay." 

Recent years have seen incredible advancements when it comes to prostheses. Back in 2016, researchers reported the first prosthesis to connect directly to muscle, nerves, and bone, which allowed an arm amputee to operate heavy machinery and handle an egg without breaking it. Earlier this year, scientists managed to wire a prosthetic hand directly into a woman’s nerves, giving her movement and a sense of touch. If this kind of tech can one day be made commercially available, it could have tangible, life-changing impacts on a huge number of people.   

"We are envisioning an aggressive, but realistic timeline of four years from now: indeed we already put together the consortium of technical (prosthetic manufacturer, electrodes manufacturer) and medical (hospitals in Italy and Germany) partners. Together with them, we'll work on the bigger clinical trial, which would aim to gather the data necessary for the certification of this technology," said Raspopovic.