2020 is slowly coming to an end. So this is the last article for this year. But before The Active Amputee heads for a holiday break, I am very happy to announce a new partnership. Larry Borowsky from Amplitude Magazin and I have decided to team up for a series of articles for 2021. This will allow us to share more information, strengthen our ties, and thus serve the limb loss community even better. Today's article by Larry on the evolution of smart prosthetics kicks off this new partnership. And I am already looking forward to more exciting conversations in the future.

Greetings from Amplitude Magazine, the top US lifestyle publication for amputees and people with congenital limb difference. We are regular readers of The Active Amputee and huge fans of Bjoern’s, so we’re grateful for the chance to contribute to the site and add our voices to the conversation. 

One of the stories Amplitude has followed closely in 2020 is the evolution of “smart prosthetics” that use remote sensing technology (and artificial intelligence, in some cases) to link the prosthesis directly to the wearer’s nervous system. Several different types of smart prosthetics made big advances this year, but the variant we’re most excited about involves peripheral nerve stimulation, or PNS. 

PNS has the potential to improve amputees’ experience in two powerful ways. First, it promises to offer unprecedented levels of sensory feedback and spatial orientation, enabling wearers to “feel” the prosthesis in ways that mirror natural sensation from an organic limb. Second, PNS seems to bring significant relief from phantom limb pain.

Here’s how it works. The prosthetic foot and knee are equipped with electronic sensors that continuously transmit wireless signals about position, contact, force, and other variables. Those signals are received by electrodes that are implanted within the amputees’ residual limb and wrapped around the major nerve(s)—the sciatic or tibial nerves, in the case of lower-limb amputees.

“The solution to more natural, controllable prostheses is interfacing the device with peripheral nerves, which remain anatomically and functionally intact after amputation,″ explains Italian bioengineer Francesco Petrini, who is leading Europe’s most advanced PNS research project. “The brain processes the information [as normal neural input], and the user is able to perceive what’s happening through their prosthesis.”

Prosthetics developers have been experimenting with PNS since the 1980s, but the technology to execute it effectively didn’t emerge until very recently. Petrini began working on neuroprosthetics in 2014 as one of the co-founders of SensArs Neuroprosthetics. In 2018 the company became a finalist in the EIT Health European Health Catapult competition, and the following year it received a €3 million research grant from the European Union’s Horizon 2020 programme to develop a PNS-equipped prosthetic leg.

Trade-named SENSY, the device has been designed in collaboration with Össur and will undergo clinical trials at the Gemelli University Hospital in Rome and the Charité–Universitätsmedizin Berlin. SensArs has already tested prototypes of the SENSY, and the results were promising enough to generate scientific publications in Nature Medicine, Science Translational Medicine, MIT Technology Review, and IEEE Brain. Participants in the prototype studies reported that the SENSY allowed them to walk with:

• Better balance
• More confident footing
• Reduced energy expenditure
• Greater endurance
• Less fatigue

This 2-minute video provides an easy-to-understand introduction to the SENSY in particular, and PNS technology in general. 

One of the US counterparts to SensArs is Ripple Neuro, a Utah-based company that’s developing its own PNS-based neuroprosthetic leg with $2 million in funding from the US National Institutes of Health. In July, Amplitude spoke with Ripple’s neurosurgical partner, Dr. Giancaro Barolat, a pain-control specialist who has worked with nerve-stimulation systems for three decades.

As Barolat tells it, innovations in prosthetic engineering are only half of what’s exciting about PNS systems. The other half lies with the sophisticated implants that will establish a clear, robust connection between the prosthesic sensors and the user’s nervous system.

“The beauty of these [new] devices is they can be integrated to control many kinds of signals,” says Barolat, who practices at Presbyterian St. Luke’s Hospital in Denver, Colorado. “The current technology is not selective for the smaller fibers that make up the nerve.” Ripple’s implants, by contrast, will differentiate between sensory nerve fibers (which convey information related to touch, temperature, pressure), motor fibers (which interact with muscles), and nociceptors (which convey pain signals). 

Barolat, who has been treating amputees suffering from phantom-limb pain for many years, says: “Hopefully this new type of device will give me better results than what I can obtain today.”

Both the SensArs and Ripple Neuro PNS devices are entering the phase of large-scale clinical trials. In addition to testing the sensing technology itself, it will be necessary to perfect the surgical implant procedures and the placement of the electrodes.

Ripple Neuro estimates its clinical trials will be complete by 2022. The same time frame likely applies to SensArs’ SENSY trials, although the company hasn’t projected a date for completion. 

Once the products have been cleared for general use, the next hurdle will be cost. Within the US, PNS-equipped smart prosthetics likely won’t be covered under most insurance plans, at least initially. But over time, it may be proven that smart prosthetics prmote overall health to such an extent that insurers will actually save money over the long run by approving these devices.

While both the SENSY and the Ripple Neuro device are being tested for leg amputees, PNS is not limited to the lower limbs. If it proves successful, the same principle can be integrated into arm prosthetics. And remember, PNS is just one type of technology within the family of smart prosthetics. Many other variants are in the works. So the next few years promise to be exciting ones for users of prosthetic technology.

Thanks again to Bjoern for inviting us to contribute. Please visit Amplitude at https://livingwithamplitude.com for ongoing coverage and commentary about living with limb loss. You can also subscribe to our free newsletter to receive weekly updates.