Johnny Matheny’s left hand is controlled like yours and mine—by thinking about it. Except Matheny’s left forearm is prosthetic, and the mind-control comes via an off-the-shelf Myo sensor that detects the gestures in his upper arm and converts them to movement.
Matheny’s arm is as cutting edge as it gets. The prosthetic itself is connected to a bayonet that’s mounted directly to the bone in his upper arm, a technique known as osseointegration. This avoids the use of a sling or socket-based prosthetic, which puts pressure on the stump. The device is inserted into the marrow of the bone, and the bone then heals around it, just like it would when healing a broken bone. This anchors the fitting as securely as if it were the patient’s own bone.
"Before, the only way I could put the prosthetic on was by this harness with suction and straps," says Matheny, "but now, with osseointegration, the implant does away with all that. It’s all natural now. Nothing is holding me down. Before, I had limited range; I couldn’t reach over my head and behind my back. Now boom, that limitation is gone."
Then, surgeons at the Johns Hopkins University Applied Physics Laboratory rewired the nerves in his arm in a procedure called targeted muscle reinnervation, reassigning the nerves that once controlled his hand to instead control the prosthetic.
Matheny controls the arm via a Myo, a gesture-control armband that anyone can buy (it’s sold on Amazon). The band senses the electrical signals from the muscles in the arm, as well as its overall motion, and sends the information to a computer. It can be used for controlling PowerPoint presentations from a PC, or it can be used, as in Matheny’s case—to control a high-tech arm.
And it works. Metheny did some off-curriculum homework, attaching a three-pound weight to the mount and exercising it during his recovery. This let him hit the tests at the Johns Hopkins lab at full power. "What ultimately happened was that Johnny met all of my planned goals within two hours of arriving," says prosthetist Courtney Moran.
The Myo requires only skin contact and weighs little more than a chunky wristwatch. "If Johnny’s case shows it is possible to directly turn thoughts into actions, then the future of human-computer interaction can achieve a new reality," said Stephen Lake, CEO of Thalmic Labs, the company behind the Myo.
If nothing else, Matheny might be wearing the only prosthetic arm that can also pilot a drone, or control YouTube videos.