Pioneering surgical breakthrough

A young woman who lost her arm in a motorbike accident has undergone a pioneering surgical technique involving the rerouting of nerves which allows her to feel she is moving her artificial limb with merely the power of thought.

Claudia Mitchell is one of only four people in the United States to have undergone the procedure, but the results will give hope to many who have lost a limb. "I just think about moving my hand and elbow and they move," she told her doctors.

Not only can she move her arm and wrist spontaneously, but the transfer of sensory nerves into a patch of skin on her chest allows her to experience the feeling of somebody touching her missing hand.
In a paper in the Lancet medical journal, published today, her doctors describe what they call the exciting implications of their surgery. It has the potential to give the patient back their sense of touch, the feeling of greater or lesser pressure on the fingers, the sensation of heat and cold and even an awareness of texture.

The case of Ms Mitchell, formerly in the US marine corps, will bring hope to many. Surgeons at the Neural Engineering Centre for Artificial Limbs at the Rehabilitation Institute of Chicago have devised a way of redirecting the severed nerves that would have sent messages from the brain to the arm and the hand.

In a process they call targeted muscle reinnervation, they remove the nerves from certain muscles in the chest and transfer into them instead the remnants of nerves that would have run down the arm.
Those muscles are linked to myoelectric sensors, which operate the artificial limb. When Ms Mitchell thinks about closing her hand, the nerve that would have made it happen causes a movement in the chest muscle to which it has been transferred. That muscle movement is picked up by the sensor and the artificial hand closes.

Restoring the sense of touch is possible in a similar way, write Professor Todd Kuiken and colleagues.
A segment of skin on the chest is denervated and the residual nerve fibres that were once responsible for sensation in the fingertips are routed into the patch. The aim, they say, would be eventually to fit sensors to the artificial fingers that could quantify pressure, temperature and the texture of objects. That would be transmitted back to a device positioned over the skin in the chest containing the sensory nerves which could apply the right pressure, temperature or sensation of texture.
Professor Kuiken said he thought the procedure was an important advance, but added: "I think we can go a lot further. We think we can extract more information from this technique to allow control of more sophisticated arms and wrists."

He and his team, funded by the US National Institutes of Health, have now operated on three more patients - two successfully and one too recently to know. They are working on developing sensors for artificial fingers they hope will feed sensation to sensory nerves in the chest.
Like many people with a high amputation - in this case, at the shoulder - Ms Mitchell was unhappy with the standard prosthetic limb she had been wearing for eight months before she underwent the surgery.
Within three months, she had first signs that the nerves were functioning in their new location. By six months, there were responses from all the nerves that had been transferred.
Within a few days of being fitted with a new prosthetic arm, Ms Mitchell was proficient in its use and could bend her hand, wrist and elbow at the same time, just by thinking about it. At time of writing, say the doctors, she was wearing it for an average of four to five hours a day, but up to 16.
The team have operated on five patients and been successful in all but one, who was discovered to have nerve damage.

Source - The Guardian

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