Modern prosthetics work better and, in some cases, look cooler, than ever before. Still, most amputees are removing them at night and reattaching them in the morning. They're not part of the body, and they do not offer the same kinds of sensations.
One Swedish amputee, however, is wearing a different kind of prosthesis — one that is actually connected to his own bone, muscles and nerves. The result is a mind-controlled artificial arm that offers more movement, less discomfort and — in the long run — actual touch sensation.
The unidentified Swedish man has been wearing this new osseointegrated (bone-anchored) implant system since January — and, according to a study published on Wednesday in the Science Translational Medicine journal, the results have been more than promising.
"We have used osseointegration to create a long-term stable fusion between man and machine, where we have integrated them at different levels," said Max Ortiz Catalan, research scientist at Chalmers University of Technology and leading author of the publication.
"The artificial arm is directly attached to the skeleton, thus providing mechanical stability. Then the human's biological control system, that is nerves and muscles, is also interfaced to the machine's control system via neuromuscular electrodes."
Traditionally, prosthetics work via sensors that sit on top of the wearer's skin. They read electrical impulses, usually created by the amputee tensing and relaxing their limb or shoulder, and transmit them to the arm, which allows it to move, turn and grasp.
This arm, though, goes deep under the skin. The Swedish patient had surgery where a titanium implant was affixed to the bone and served as a kind of bionic bone extension. Electrodes were implanted in the patient's muscle and nerves. Not only do they allow the patient to control the arm, but they are also able to receive transmissions from sensors in the prosthetic arm and hand.
Having a prosthetic arm attached this way means there's no socket to attach the arm to — it's worn more or less continuously. The researchers claim such "intimate connection" improves overall comfort and control.
Mind control options
This isn't the first time a sense of touch has been added to prostheses. There's the Deka or "Luke" arm — and in February, a team of researchers from Italy, Switzerland, Germany, Britain and Denmark published a study, also in the Science Transnational Medicine journal, which described how they implanted electrodes in a patient's arm, attached them to his nerves and then connected them to a prototype prosthetic hand.
The patient, Dennis Aabo Sorensen, could, according to a Reuters report, feel objects and sense their shapes, even when blindfolded. Sorensen, who lost his hand in a fireworks accident, told Reuters: "It was pretty close to having the same feeling as in my normal hand."
But Sorensen's experience was mostly in the lab. The Swedish recipient of the mind-controlled prosthesis has been using the arm while on the job (he drives a truck).
The arm has worked reliably since implantation, but is not yet delivering sensory feedback from the arm to the brain.
"We see this technology as an important step towards more natural control of artificial limbs," Ortiz Catalan, the research scientist at Chalmers University of Technology, said. "It is the missing link for allowing sophisticated neural interfaces to control sophisticated prostheses. So far, this has only been possible in short experiments within controlled environments."
No word on when or if researchers will commercialize their osseointegration method. But they do plan on treating more patients with the technology later this year.