MIND CONTROLLED PROSTHETIC ARMS THAT WORK IN DAILY LIFE ARE NOW A REALITY
For the first time,
robotic prostheses controlled via implanted neuromuscular interfaces have
become a clinical reality. A novel osseointegrated (bone-anchored) implant
system gives patients new opportunities in their daily life and professional
activities.
In January 2013 a
Swedish arm amputee was the first person in the world to receive a prosthesis
with a direct connection to bone, nerves and muscles. An article about this
achievement and its long-term stability will now be published in the Science
Translational Medicine journal.
"Going beyond the
lab to allow the patient to face real-world challenges is the main contribution
of this work," says Max Ortiz Catalan, research scientist at Chalmers
University of Technology and leading author of the publication.
"We have used
osseointegration to create a long-term stable fusion between man and machine,
where we have integrated them at different levels. 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."
The direct skeletal
attachment is created by what is known as osseointegration, a technology in
limb prostheses pioneered by associate professor Rickard Brånemark and his
colleagues at Sahlgrenska University Hospital. Rickard Brånemark led the
surgical implantation and collaborated closely with Max Ortiz Catalan and
Professor Bo HÃ¥kansson at Chalmers University of Technology on this project.
The patient's arm was
amputated over ten years ago. Before the surgery, his prosthesis was controlled
via electrodes placed over the skin. Robotic prostheses can be very advanced,
but such a control system makes them unreliable and limits their functionality,
and patients commonly reject them as a result.
Now, the patient has
been given a control system that is directly connected to his own. He has a
physically challenging job as a truck driver in northern Sweden, and since the
surgery he has experienced that he can cope with all the situations he faces;
everything from clamping his trailer load and operating machinery, to unpacking
eggs and tying his children's skates, regardless of the environmental
conditions (read more about the benefits of the new technology below).
The patient is also
one of the first in the world to take part in an effort to achieve long-term
sensation via the prosthesis. Because the implant is a bidirectional interface,
it can also be used to send signals in the opposite direction -- from the
prosthetic arm to the brain. This is the researchers' next step, to clinically
implement their findings on sensory feedback.
"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 Max Ortiz Catalan. "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 researchers plan
to treat more patients with the novel technology later this year.
"We see this
technology as an important step towards more natural control of artificial
limbs," says Max Ortiz Catalan. "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."
More about: How the
technology works
The new technology is
based on the OPRA treatment (osseointegrated prosthesis for the rehabilitation
of amputees), where a titanium implant is surgically inserted into the bone and
becomes fixated to it by a process known as osseointegration (Osseo = bone). A
percutaneous component (abutment) is then attached to the titanium implant to
serve as a metallic bone extension, where the prosthesis is then fixated.
Electrodes are implanted in nerves and muscles as the interfaces to the
biological control system. These electrodes record signals which are
transmitted via the osseointegrated implant to the prostheses, where the
signals are finally decoded and translated into motions.
More about: Benefits
of the new technology, compared to socket prostheses
Direct skeletal
attachment by osseointegration means:
Increased range of motion since there are no physical
limitations by the socket -- the patient can move the remaining joints freely
Elimination of sores and pain caused by the constant pressure
from the socket
Stable and easy attachment/detachment
Increased sensory feedback due to the direct transmission of
forces and vibrations to the bone (osseoperception)
The prosthesis can be worn all day, every day
No socket adjustments required (there is no socket)
Implanting electrodes
in nerves and muscles means that:
Due to the intimate connection, the patients can control the
prosthesis with less effort and more precisely, and can thus handle smaller and
more delicate items.
The close proximity between source and electrode also prevents
activity from other muscles from interfering (cross-talk), so that the patient
can move the arm to any position and still maintain control of the prosthesis.
More motor signals can be obtained from muscles and nerves, so
that more movements can be intuitively controlled in the prosthesis.
After the first fitting of the controller, little or no
recalibration is required because there is no need to reposition the electrodes
on every occasion the prosthesis is worn (as opposed to superficial
electrodes).
Since the electrodes are implanted rather than placed over the
skin, control is not affected by environmental conditions (cold and heat) that
change the skin state, or by limb motions that displace the skin over the
muscles. The control is also resilient to electromagnetic interference (noise from
other electric devices or power lines) as the electrodes are shielded by the
body itself.
Electrodes in the nerves can be used to send signals to the
brain as sensations coming from the prostheses.
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