A prosthetic arm connected directly to the bone, nerves and muscles has been found to be a success. This is the first time that a robotic prosthesis has been connected in such a manner, and this discovery will open up exciting opportunities for patients in the future.
The arm, controlled with implanted neuromuscular interfaces, was given to an arm amputee patient in January 2013, and an article about its long-term stability and effectiveness has now been published in the journal Science Translational Medicine.
Leading author Max Ortiz-Catalan, a research scientist at Chalmers University of Technology in Gothenburg, Sweden, says their work goes beyond the laboratory to allow the patient to face real-world challenges.
The patient in question had his arm amputated 10 years ago. Prior to being given the new arm, his prosthetic arm was controlled using electrodes placed over the skin.
This typical form of control system can be unreliable, limiting how useful prosthetics can be. As a result, many patients reject them as a form of rehabilitation.
'A union between body and machine'
The new implant system uses a titanium implant connected directly into the bone of the arm, as part of a process called osseointegration. This creates a long-term stable fusion between the patient and their implant, which Dr. Ortiz-Catalan explains in detail:
"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."
Connecting electrodes directly to the nerves and muscles means that patients can control their prosthesis more easily and with greater precision, enabling them to handle smaller and more delicate items.
Due to the close proximity between the electrodes and the nerves controlling the device, activity from other muscles is prevented from interfering with the device, allowing the patient to move the arm into any position without having to worry about losing control of it.
The osseointegration technology was pioneered by Associate Prof. Rickard Brånemark and his colleagues at Sahlgrenska University Hospital in Gothenburg, Sweden. Prof. Brånemark led the implantation surgery and worked closely with Dr. Ortiz-Catalan and Prof. Bo Håkansson, of the Chalmers University of Technology, for the rest of the project.
Could this be the 'missing link'?
The patient who received the new prosthetic system has been able to use it successfully when facing the physical demands of his day-to-day life. The patient works as a truck driver and has had no problems with routine activities such as clamping his trailer load or operating machinery.
He is equally able to perform actions requiring a little more delicacy, such as unpacking eggs or tying up the laces on his children's skates - actions that other prosthetic devices may not have been able to perform comfortably. The team now intends to treat further patients with this new ground-breaking technology over the next few months.
The next step for this research is to achieve long-term sensation for the patient via the prosthesis. This new form of implant is a bidirectional interface; not only can the prosthetic arm receive signals from the brain, but also the brain can receive signals coming in the opposite direction.
"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," says Dr. Ortiz-Catalan, adding:
"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."
Dr. Ortiz-Catalan sees the technology as an important step toward a more natural control of artificial limbs. "It is the missing link for allowing sophisticated neural interfaces to control sophisticated prostheses," he says. "So far, this has only been possible in short experiments within controlled environments."