Friday, September 15, 2006
Bionic woman
No, not Lindsay Wagner. Her name is Claudia Mitchell, and she lost her arm in a motorcycle accident.
The process doctors used to create a responsive prosthetic arm for her is nothing less than a medical wonder:
In preparation for the bionic arm, Kuiken and his surgical colleagues first re-create a biological control panel for a hand on the amputee's chest. They use muscle and skin that can be sacrificed -- or, more precisely, hijacked -- for that purpose.
They cut the nerves to two chest muscles, the pectoralis and serratus, at a point where those nerves have branched to go to different parts of the muscles, but far "upstream" from the point where the nerves divide into tiny fibers that attach to individual bundles of muscle fiber.
They then sew the stumps of the large nerves that once went to the arm and hand to the cut ends of the chest-muscle nerves. In the same operation, the nerves carrying sensation from the skin over the pectoral muscle are also sewn into the arm nerves.
Over several months, the arm nerves grow down the sheaths of the motor fibers and attach to the muscles. (Interestingly, the amputee assists this process by mentally "exercising" the missing hand, which helps promote a firm nerve-muscle connection.) Simultaneously, the sensory nerves grow down the sensory sheaths and into the skin.
If all goes well, a person is left with chest muscles that twitch in different places in response to such thoughts as "bend the wrist back," "move the thumb" and "clench the fingers." The person also ends up with a patch of skin about the width of a baseball that, when stroked, warmed or pricked, feels like a hand rather than part of the chest.
The bionic arm makes use of this feat of anatomical alchemy.
The prosthesis is strapped onto the shoulder stump and torso in a way that positions electrodes over the regions of the chest muscles that are responding to different "hand instructions." Those electrodes, in turn, are wired to a computer and then on to motors in the forearm and hand of the device.
When the amputee tells the fingers to close, the designated part of the pectoral or serratus muscle twitches and the electrode over it detects the signal, activating the appropriate motor.
Wow. That's all, just wow. Do read the whole thing.
The process doctors used to create a responsive prosthetic arm for her is nothing less than a medical wonder:
In preparation for the bionic arm, Kuiken and his surgical colleagues first re-create a biological control panel for a hand on the amputee's chest. They use muscle and skin that can be sacrificed -- or, more precisely, hijacked -- for that purpose.
They cut the nerves to two chest muscles, the pectoralis and serratus, at a point where those nerves have branched to go to different parts of the muscles, but far "upstream" from the point where the nerves divide into tiny fibers that attach to individual bundles of muscle fiber.
They then sew the stumps of the large nerves that once went to the arm and hand to the cut ends of the chest-muscle nerves. In the same operation, the nerves carrying sensation from the skin over the pectoral muscle are also sewn into the arm nerves.
Over several months, the arm nerves grow down the sheaths of the motor fibers and attach to the muscles. (Interestingly, the amputee assists this process by mentally "exercising" the missing hand, which helps promote a firm nerve-muscle connection.) Simultaneously, the sensory nerves grow down the sensory sheaths and into the skin.
If all goes well, a person is left with chest muscles that twitch in different places in response to such thoughts as "bend the wrist back," "move the thumb" and "clench the fingers." The person also ends up with a patch of skin about the width of a baseball that, when stroked, warmed or pricked, feels like a hand rather than part of the chest.
The bionic arm makes use of this feat of anatomical alchemy.
The prosthesis is strapped onto the shoulder stump and torso in a way that positions electrodes over the regions of the chest muscles that are responding to different "hand instructions." Those electrodes, in turn, are wired to a computer and then on to motors in the forearm and hand of the device.
When the amputee tells the fingers to close, the designated part of the pectoral or serratus muscle twitches and the electrode over it detects the signal, activating the appropriate motor.
Wow. That's all, just wow. Do read the whole thing.
