21 March, 2008
WORKING PRINCIPLE OF FIRST BIONIC ARTIFICIAL ARM
(CLICK PICTURE TO ENLARGE)
A woman fitted with the world's first "bionic arm" controlled by thought alone has been given back a sense of feeling.
Claudia Mitchell, 26, a former US marine, regained the ability to carry out simple tasks such as cutting up food when she was fitted with the prosthetic arm last year.
Now doctors have re-routed the ends of arm nerves to a patch of skin on her chest — allowing her to regain the sensation of having her lost hand touched.
A new study of her wrist, hand and elbow function found she could use the artificial limb intuitively and could perform tasks four times quicker than with a conventional prosthesis.
Ms Mitchell, who had her left arm amputated after a motorcycle accident, told doctors: "I just think about moving my hand and elbow, and they move. I think, 'I want my hand open' and it happens. My original prosthesis wasn't worth wearing — this one is."
In a commentary published in The Lancet medical journal, Dr Leigh Hochberg, a neurologist at Massachusetts General Hospital, said early results for the new operating system for the limb were "an important step forward in the seamless integration of replacement limbs into the body".
Dr Hochberg said the next stage would be for touch sensors on the artificial hand transmitting signals back to the re-routed nerves, allowing patients to have accurate sensations of touch, temperature and joint position.
Motorised hooks, hands, wrists and elbows are currently available but movement is usually slow and awkward. Scientists have long been working to create a limb that is controlled by the brain and works well while looking near-normal.
The new technique — called targeted muscle reinnervation (TMR) — involves re-routing nerves that once controlled the patient's arm to a patch on the chest, where they grow into muscles. Electrodes on the surface of the chest skin pick up brain signals from the nerves and send signals to operate the artificial arm.
When Ms Mitchell thinks about moving her hand or arm, the nerves react as if they were still leading all the way down her arm and into the elbow and fingers.
If someone touches the patch of skin on her chest it feel as if they are touching her hand. Scientists are working on sensors for the artificial hand that would communicate with the re-routed nerves to provide a patient with the same sensations they would have felt before amputation.
Dr Todd Kuiken, from the Rehabilitation Institute of Chicago, the leader of the medical team that developed the technology, said: "The brain doesn't know that these nerves are connected to different tissue or muscle."
Ms Mitchell began to feel the muscles in her chest twitching when she tried to close her hand or bend her elbow three months after the operation to re-route the nerves. After six months the new 11lb artificial limb was fitted and she became proficient in using it after a few days.
She practised using the limb four to five hours a day, five to six days a week, and was able to operate her hand and elbow "intuitively" within seven weeks of the fitting.
Pressing pressure-sensitive buttons allowed the wrist to rotate at the same time as other movements were being made.
Ms Mitchell was able to complete a task involving moving blocks into boxes four times quicker with the new prosthesis than the conventional one.
In tests of her ability to put on make-up, eat, clean and do the laundry, the bionic arm helped her perform up to six times quicker.
Dr Kuiken, whose work is funded by the US National Institutes of Health, said eight patients had been fitted with the new system, and that it was hoped US soldiers returning from Iraq could benefit from the technology.
He added: "With training, the patient became proficient in use of the prosthetic within a few days.
"She was able to operate the hand, wrist and elbow simultaneously.
"She reported that operation of the hand and elbow was very intuitive: when she thought of opening the hand, closing the hand, bending the elbow, or straightening the elbow, the prosthesis responded.
"Whether the improved function is enough to keep the patients wearing their devices in years to come, or whether they adapt to their new control even better and show greater functional gain remains to be seen."