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29 March 2004

Prostheses - help is at hand

In every schoolboy’s lexicon of imagination there was a bionic device of some sort that could make life easier. But in real life, there have been some astonishing developments in bionic prostheses.

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In every schoolboy’s lexicon of imagination there was a bionic device of some sort that could make life easier – a hand that answered maths papers without needing input from the brain, or a robot that tidied up your room.

Men of a certain age will remember the TV series Six Million Dollar Man, translated into Afrikaans as Man Van Staal, along with all the other decent overseas shows.

In it, Lee Majors was an astronaut who’d pranged his spacecraft on re-entry and all but destroyed his body. Yet, intoned the drawling, booming Voice-of-God narrator: “We can rebuild him – we have the technology.”

Majors’ stricken character was fitted with bionic substitutes for all his damaged bits – both legs, an arm and an eye – and set of to fight the forces of communism, terrorism and dental decay wherever they might be found.

Artificial limbs nothing new
But in real life, there have been some astonishing developments in bionic prostheses.

Artificial limbs have been around for centuries: in around 880 BC, a Persian warrior named Hegesistratus is reputed to have hacked off his foot to escape the shackles of his captors. He later made himself a wooden foot, which he was careful to keep from termites.

That was about the most sophisticated that prostheses got for a long time. If you lost a leg you got a peg. Losing a hand got you a hook. Losing both got you a bargain on a parrot, a discount at your local drycleaners and permission from the Admiralty to say “Arrrr, me hearties” a lot.

First artificial knee joint in 1529
It wasn’t until 1529 that a French army surgeon worked out how to put a joint at the knee of an artificial leg.

This surgeon and Captain Hook would’ve been intrigued to read about the new advances in prosthetics, which marry microsurgery, electronics, miniaturization and the talents of scientists from four European countries.

As with all reporting on science, saying anything is promising or verging on a breakthrough could mean it’s years away – that doesn’t mean it’s not exciting. That’s especially true when amputees of the future will probably be able to wear a bionic limb that’s wired directly into their nervous system.

Future prosthetics thought-controlled
Not only will they be able to operate their prosthetics by thought alone, but they’ll be able to receive sensations back from the limbs, like pressure, heat and vibration.

There are already sophisticated prosthetic hands available that are made to open and close by electromyography, where sensors worn on the arm detect activity in the arm muscles and trigger actions by the little motors that operate the hand. It operates on rechargeable batteries.

The wearer can operate the hand by simply flexing their arm muscles. This is fine, because it allows some movement. The problem with these prostheses is the lack of nerve contact. It’s really like trying to pick up a pin with two sticks.

Human hand a very complex thing
It’s a testimony to the complexity of the human hand: it can tickle the ivories or a tickle a child’s toes, it can peel an orange, open a stubborn jam jar, or feel for a light switch in a dark room; it picks up a wineglass without letting it slip or crushing it.

To do that it must be able to get sensory feedback from the fingertips. Bionic hands can’t do that yet. But the magazine New Scientists reports that the Cyberhand, which could be available commercially in about five years, will be connected directly to the nervous system. This won’t mean that the user will have wires sticking out of the flesh of the stump – that risks infection and other problems. Instead, a network of tiny electrodes will be implanted in the arm and fixed to nerves in the tissue.

Scientists are experimenting with making nerves in the stump grow onto the electrodes. These are then joined to a transmitter under the flesh of the stump. It interfaces with a transmitter in the prosthesis, which in turn links to touch sensors in the hand and fingertips. There’ll be four types of sensor in the skin, relaying different types of pressure through the two transmitters and back to the brain. In turn, the brain will be able to control the Cyberhand.

New technology may help the paralysed
The same technology being developed to help the Cyberhand get a grip may one day help Superman.

Few people would have missed the tragic irony of the accident that left Christopher Reeve paralysed – the man who played an invincible superhero confined to a wheelchair. While the trauma to his spinal cord means his brain has no contact with the rest of his body, his arm and leg muscles are still functional.

So by-passing the damaged area of the spine could help Reeve and others like him. Scientists at the University of Technology in Sydney, Australia, are experimenting with a cap that is implanted with electrodes that measure electrical activity in the brain.

It may be combined with another system called functional electrical stimulation (FES), which is already used by some physiotherapists to help paralysed patients retain muscle tone.

Essentially it involves a controlled electric current to an electrode on the skin, which causes the muscle to contract.

Marrying these two systems could mean that paraplegics would be able to get up and walk by doing little more than thinking about it. (William Smook)

 
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