It took some time, but the age of the cyborg is upon us. For the first time, neuromuscular electrodes that enable a prosthetic arm and hand to be controlled by thought have been permanently implanted into the nerves and muscles of an amputee. The operation was carried out recently by a surgical team led by Dr Rickard Brånemark at Sahlgrenska University Hospital in Goteborg, Sweden.

We first covered the Chalmers University artificial arm last November. It goes a step beyond current motorized prostheses as it is intended as a permanent part of the patient’s body. This helps to solve the two main problems of such prostheses: the socket to fit the arm to the patient and the pickups used to control it.

Instead of a tight, uncomfortable socket fitted to the arm stump, the Chalmers University arm is attached to the stump by fusing a titanium socket to the bone itself in a procedure called osseointegration. The skin pickups used in many mechanical arms to provide the user with control by muscle impulses are replaced by electrodes that have been permanently implanted in nerves and muscles, so commands can come directly from the brain to the arm. While the arm itself can be detached, the socket and electrodes are permanent.

Rickard Brånemark of Sahlgrenska University Hospital, who helped develop the implant technology, says this bone-anchored approach, "allows complete degree of motion for the patient, fewer skin related problems and a more natural feeling that the prosthesis is part of the body. Overall, it brings better quality of life to people who are amputees.

According to Brånemark, the implants provide more functionality because they allow more signals to be retrieved than is possible with electrodes placed over the skin. They also have the potential to send signals back to the brain and give the patient a sense of "feeling."

“We believe that implanted electrodes, together with a long-term stable human-machine interface provided by the osseointegrated implant, is a breakthrough that will pave the way for a new era in limb replacement,” said Brånemark.

The first patient, who has not been named, had the arm recently – for want of a better word – installed and, according to Chalmers University, the first test results have been “excellent.” The patient said that the arm works with almost no effort in generating control signals, that more movements can be performed than with the patient's previous robotic hand, and that several movements can be carried out at once.

As to the future, Brånemark said, “the next step will be to test electrical stimulation of nerves to see if the patient can sense environmental stimuli, that is, get an artificial sensation. The ultimate goal is to make a more natural way to replace a lost limb, to improve the quality of life for people with amputations.”

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