New Stimulator System Designed to “Restore” Feeling in Amputated Limbs

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Weber developed the Phantom-Stimulator system, a device designed to trigger nerves that have been shown to produce sensation in a prosthesis user’s missing limb. Photograph courtesy of Theresia Weber.

In 1998, Karl-Heinz Weber was on a business trip in the United Kingdom when he broke the tibia and fibula in his right leg while descending a flight of stairs. The healing process for his broken leg was arduous at best. The break was a total open fracture with heavy bleeding through a damaged artery and a deep vein; he also developed a bone infection and blood poisoning, which were nearly fatal, he says. "As a result, I needed to continuously use antibiotics and painkillers," recalls Weber, who was 42 years old at the time. "This was a very long and difficult journey for me."

The bone infection failed to heal. By 2008, the pain in Weber's leg had become so unmanageable he could hardly walk. His quality of life suffered drastically, remembers Weber, who lives in southern Germany and is an avid motorcyclist.

"My doctors could no longer do anything to help my situation," he says. "Hence the decision was made to remove my leg below the knee in January 2009."

Tony Petrecca has been a friend and business partner of Weber's for more than 30 years. He clearly remembers his friend's constant pain. "It was amazing that he was able to hold onto his leg for as long as he did," Petrecca says.

A Serendipitous Moment

As Weber, an electronic engineer by trade, worked to adjust to and become comfortable using his new prosthesis, he began to search for more and improved ways to feel and control it. He especially wanted to feel his leg while riding his motorcycle—to make sure his foot was securely on the foot peg, he says. He couldn't do that, however, without continually looking down at it. It became a constant source of frustration.

Then one day Weber was sitting in his office with his right forearm resting on the edge of his desk when he remembers having an odd but distinct sensation of feeling in his missing right toe. In fact, there were days when Weber says he could feel his missing leg as though it were still a part of his physical body.

In the beginning, Weber says he was reluctant to tell anyone. "I didn't want anyone to think I was crazy," he says. "But this missing part, phantom, was coming and going for a while, so I decided to discuss this with my rehabilitation doctor."

Weber says he was relieved to learn from his rehabilitation physician that such a feeling was "a very common phenomenon." Tactile stimulation of certain parts of the hand or arm on the same side as the amputation can elicit a feeling in certain parts of the phantom foot, Weber says he was told.

It was during these discussions that Weber's rehabilitation physician told him about Alfred Meier-Koll, Prof. Dr. rer. nat., Dr. med. habil., the head professor of the DIPLOMA Research Centre for Experimental Physical and Occupational Therapy, Friedrichshafen, Germany.

Meier-Koll, who is also a physician specializing in neurology and physics, and Weber became fast friends. Neither of the men knew it at the time, but they would soon become business partners.

A field test patient, with sensors installed in his shoe, uses the Phantom-Stimulator. Photographs courtesy of Karl-Heinz Weber.

A patient demonstrates standing on his prosthesis while on a trampoline using the Phantom-Stimulator. Electrodes have been placed on the receptive nerve fields of his left hand.

"He told me it is widely known that amputees have sensations in the phantom limb," Weber says. "I told him that when I lightly touch and scratch some areas on my right arm, this makes me feel that my missing leg is no longer missing and that some areas of it have feeling."

Weber says many others who use lower-limb prostheses similarly describe the observation of phantom limb sensations pointed out to him by Meier-Koll, which provided him the incentive to observe this phenomenon in greater detail.

A Business Opportunity

In 2012, Weber, Meier-Koll, and Petrecca formed CortXSenSorics Neuro Prosthetic Systems, Spaichingen, Germany; two years later they opened an office in St. Catharines, Ontario, Canada. Petrecca, based in the Canadian office, is the production manager coordinator and one of the managing directors of the company along with Weber and Meier-Koll.

Weber and Meier-Koll began working together to create and develop what they call the Phantom-Stimulator system, a device that is designed to trigger the nerves that have been shown to produce sensation in the missing limb when the prosthesis is active or in use. With the stimulator system, switches and load sensors are placed in the sole of the prosthetic foot. The switches produce on/off signals with a connected "electronic black box" that is attached to the prosthesis, Weber says. The black box transmits the signals wirelessly to a receiver that generates signals through electrodes that are sent to the nerves and nerve field over the skin.

With sensation in the missing lower limb "restored," the user has been shown to have improved balance, posture, and gait, as well as know when the foot is in contact with the ground or another surface that stimulates the load sensors.

Petrecca says, "It was a fluke moment that has morphed into this [company]. Karl literally stumbled across [the stimulator system] because of his amputation."

Weber and Meier-Koll created the Phantom-Stimulator in Germany in 2012, and the first of two live field tests began in Europe a year later.

"This is a noninvasive system that does not require surgery or special medical intervention to implement," Weber says. "The solution was clear, that we can stimulate nerves or nerve fields to make the missing part feel again. If the nerve zone is not continuously triggered, the feeling disappears after a while."

Weber estimates that he wears the Phantom-Stimulator between four and six hours per day when he is home in Germany. "After I take it off, it takes awhile to lose the feeling, and I am controlling all positioning and balancing of the prosthesis with my eyes. Without the system I can't clearly point to the areas on the ground," he says. With the system installed and switched on, Weber says he also has a smoother and more relaxed walking style.

Tests, Tests, and More Tests

The first field test gave CortXSenSorics more thorough information about how the Phantom-Stimulator would work. Results from the first phase were used to implement changes and enhancements for redesigns, as well as to find more practical solutions. "The first prototype could not be used all day," says Weber. "It was too heavy and did not fit as universal equipment." In addition, it was difficult to install, he says. Weber redesigned the product, developing a new prototype that was lighter and easier to use and install.

The second phase of testing is an ongoing field test. Petrecca says more than 100 people have been testing the device in Germany and Canada. Each person wearing the prototype has a different type of lower-limb amputation.

Results have not only been positive, but nearly the same, he says. "None of those being tested know each other, but their feedback has been identical. They have all reported having a sense of feeling in their missing leg," says Petrecca, who, when the device was placed on his arm, described the feeling as similar to putting his tongue on the terminals of a 9-volt battery.

"It's a slight tingling sensation of low-voltage electricity on your skin," Petrecca says. "An amputee does not feel that sensation."

A Life Changed

Weber says the stimulating system has transformed his life. "I am back to normal and have completely stopped using pain medication," he says. "With our Phantom-Stimulator, I feel my prosthesis like my real leg. I can feel my heel, the ball of my foot, and toes."

The device also has worked particularly well for another one of CortXSenSorics' test patients, a 50-year-old physician from Germany who lost his sight and left leg to a multiresistant staphylococcus infection eight years earlier, Petrecca says. This test patient wears a hip disarticulation prosthesis. Receptive fields that could be elicited from phantom sensations for the ball and the heel of his left foot were mapped on the inner and outer skin of his left hand. Phantom sensations for his calf and big toe could be obtained from two small areas on his left arm. Due to his vision impairment, he has no visual control of his gait, Petrecca says. However, using the Phantom-Stimulator system, the test patient was not only able to balance his body while wearing his prosthesis on the vibrating ground of a trampoline, but could also climb a ladder, according to Petrecca.

A Pending Patent

The final patent for the stimulating system is pending. CortXSenSorics anticipates approval this spring, Petrecca says. Once the patent publishes, it will become available worldwide to companies that make prosthetic devices, he says. Petrecca believes the Phantom-Stimulator would also be of great interest to medical physicians and physical therapists dealing with those who have amputations.

Nothing would make the men happier.

"Karl is a remarkably strong-willed man," Petrecca says. "This really speaks to his character. I was side-by-side, watching him suffer for so many years. To see him now, he's a totally different person."

Betta Ferrendelli is a freelance writer based in Denver.

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