Earlier this year, the lab of Dr. Rickard Branemark at Sahlgrenska University Hospital was the first to permanently implant electrodes into the nerves and muscles of an amputee in order to allow them to directly control an osseointegrated prosthetic arm.
The arm itself is anchored directly to the user’s bone using a titanium screw. This medical advance will allow those with the implanted prosthetic to control it in a way that is much more similar to controlling a natural limb than anything available to date. Dr. Branemark stated 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.”
The theoretical framework for this technology was explained by Neurogadget last year; to summarize, electrodes detect signals from the nerves and muscles in the stub, and control the prosthetic much as they would control the muscles of a natural hand. However, up until now, these electrodes have only been placed on the surface of the skin. Without implanting the electrodes under the skin, the signal was too unstable to allow for reliable functionality due to the fact that the electrode placement changed every time the user’s skin stretched.
By connecting the electrodes directly to the nerves and muscles, researchers are able to allow for much more reliable control of the prosthetic. The operation was possible thanks to new advanced technology developed by Max Ortiz Catalan, supervised by Rickard Brånemark at Sahlgrenska University Hospital and Bo Håkansson at Chalmers University of Technology.
To give you an idea how the osseointegrated prosthetic arm will work in the future this video makes a very good illustration:
The implanted device is “Osseointegrated”, meaning that it is connected directly to the remaining bone. Osseointegration circumvents many of the issues inherent in socket prosthetics. According to Dr. Branemark, “It 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.”
Initial tests with the implanted limb have shown a great degree of success. The user is able to perform movements in a coordinated manner, and even perform several movements simultaneously. Furthermore, they noted that the limb functioned well in hot or cold environmental conditions, which was a limitation of the prosthetic they were using previously. It remains to be seen whether or not the implanted electrodes will allow the user to receive sensory feedback from the limb, an ability which has recently been demonstrated to be possible.