A Swedish amputee has become the first person in the world to be fitted with a prosthetic that directly interfaces with his bone, muscle and nerves, and can be controlled with his mind, making him what could be considered a true cyborg.
The patient, whose right arm was amputated 10 years ago, received the prosthesis in January 2013.
"We have used osseointegration to create a long-term stable fusion between man and machine, where we have integrated them at different levels," explained lead study author Max Ortiz Catalan, research scientist at Chalmers University of Technology, Sweden.
"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. This creates an intimate union between the body and the machine; between biology and mechatronics."
Osseointegration involved surgically implanting and fixing a titanium implant directly into the bone. An extension is then fixed to the implant, which allows the prosthesis to be attached. Electrodes are then implanted directly into the nerves and muscles; these read the electrical signals sent from the brain, which are translated into movements to be executed by the arm.
Although there are sophisticated robotic prostheses currently available commercially, these use non-invasive electrodes placed on the wearer's skin, which limits what they can do. The Swedish patient had, prior to his surgery conducted by associate professor Rickard Brånemark and his colleagues at Sahlgrenska University Hospital, Sweden, worn just such a prosthesis.
Since the surgery, he has been able to do his physically demanding job as a truck driver, completing tasks such as clamping his trailer load and operating machinery -- as well as more delicate day-to-day tasks such as handling eggs and tying the laces on his children's skates.
The direct skeletal attachment has allowed an increased range of motion compared to a myoelectric prosthesis, elimination of pressure sores from the socket, and increased sensory feedback from vibrations through the bone. Meanwhile, the implanted electrodes prevent interference from other muscles, and can read a greater number of motor signals directly from the muscle compared to the skin -- meaning a greater degree of control.
The next step is developing feeling. While most of the information is coming from the brain to the prosthetic, the implanted electrodes in the nerves can be used to send information from the prosthetic to the brain. The research team is already working towards this.
"Reliable communication between the prosthesis and the body has been the missing link for the clinical implementation of neural control and sensory feedback, and this is now in place," Ortiz Catalan said.
"So far we have shown that the patient has a long-term stable ability to perceive touch in different locations in the missing hand. Intuitive sensory feedback and control are crucial for interacting with the environment, for example to reliably hold an object despite disturbances or uncertainty. Today, no patient walks around with a prosthesis that provides such information, but we are working towards changing that in the very short term."
The full paper has been recently published and can be read online in the journal Science Translational Medicine. You can see the prosthesis in action in the videos below.