A carpenter's missing hand now talks to his robot arm through a sensor under his skin

Michael Easy is a 32-year-old carpenter from Hastings, a town southeast of Melbourne. He has a limb difference, and for the past few months he has been controlling his prosthetic arm with a strip of electronics tucked under the skin of his forearm.

"This implant has made everything easier and smoother and faster," he said, in a statement relayed by the company that made it.

On October 20, Austin-based Phantom Neuro announced that the first participants in its CYBORG early feasibility study have received its Phantom X implant. It is the first time the company's sensor has gone into people. According to IEEE Spectrum, two patients have been implanted so far, and the announcement came about five months after the first procedure.

Reading what the muscles still remember

The idea starts from something amputees know well. The hand may be gone, but the brain still sends commands to it, and the muscles left in the forearm still twitch in response. "Most people who have lost their limbs still have the ability to control their limbs," said Phantom Neuro founder and CEO Connor Glass. The trick is catching those signals cleanly enough to drive a robot hand.

Most prosthetic arms that do this today use surface electrodes pressed against the skin inside the socket. They work, sort of. As IEEE Spectrum explains, surface sensors are touchy about placement, sweat, skin movement and motion, and they can be uncomfortable to wear all day. Some systems need recalibrating every day.

Phantom's answer is to move the sensor a few millimeters inward. The implant is about 2 by 10 centimeters and wraps around the forearm under the skin, on top of the muscles, with two rows of electrodes set in flexible medical silicone. A small disk of electronics at one end processes the signals and sends them out wirelessly. A coil in the middle picks up power from outside the body, the same trick cochlear implants use. Machine learning software matches the muscle patterns to gestures and passes the commands to a compatible prosthetic hand from another manufacturer.

The surgery is the selling point. Dr. Michael Lo, a plastic and reconstructive surgeon, did the procedures at Cabrini Health in Melbourne. Each was an outpatient job of about an hour, done without general anesthesia. Glass described it as "more like a cosmetic procedure than brain surgery." Easy's operation ran about an hour under mild sedation, around four hours start to finish. The second patient's took about 45 minutes, and that person went home within three hours.

"It was a bit sore and tender for the first couple of days and then it healed so quick, there was no drama whatsoever," Easy said. He had some swelling for about two weeks.

Compare that to the brain-computer interface crowd. Neural implants in the motor cortex can read intent with remarkable detail, but they need a hole in the skull. For someone who has lost a hand and still has a working forearm, that is a big ask. Phantom is betting that the forearm is close enough to the source.

What it can and can't do yet

Phantom says the muscle signals have been strong and consistent, and that the mapping between intent and gesture may hold for months without recalibration. The system can perform the same movement at different speeds. It can't yet combine movements, such as rotating the wrist while closing the fingers, and some tasks still have to be broken into steps.

Outside experts who spoke to IEEE Spectrum liked the concept and the form factor but wanted more public technical detail. Helen Huang, a biomedical engineer at North Carolina State University, said: "I see a tremendous potential benefit for patients to use every day more reliably." Loredana Zollo of Università Campus Bio-Medico di Roma was more guarded: "Ultimately, these potential advantages must translate into tangible benefits for users."

That caution is fair. Two patients is an anecdote with a press release attached. Phantom X is investigational and not approved for sale anywhere, and the company itself says conclusions about safety and better prosthetic control will need more evaluation. The CYBORG study plans to enroll up to ten people with below-the-elbow amputations, according to The O&P EDGE, with each person evaluated over roughly 20 weeks.

Glass told IEEE Spectrum he expects FDA approval for upper-limb prosthesis control in two to three years if the trial goes well.

Then there is the line near the bottom of the Spectrum piece. Beyond lower-limb uses, Phantom is also exploring defense applications, including augmentation and human-machine interaction. A sensor that turns muscle twitches into wireless commands doesn't care whether the person wearing it has lost a hand. It would work just as well on a soldier with two, steering a drone.

For now, though, the device is doing one specific job for one carpenter in Victoria, and he says his day goes faster.

Sources: IEEE Spectrum, Phantom Neuro press release (PR Newswire), The O&P EDGE.