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 Prosthetic Arms: State of the Art, 4th Q 2007

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Date posted: 25/10/2007

Prosthetic arm development?s rapid pace is one of the very few good things to have come out of the conflict between western societies and the Middle East. In one year, they have lept from simple claws, to arms capable of picking up a skittle and passing to the wearer?s mouth.

Things started to really move along in January this year, when ex-Marine Claudia Mitchell, who ost her arm in a motorcycle accident two years ago, became the first woman to be fitted with a bionic arm.

Claudia Mitchell with her new arm

The arm was different to all that had come before, in that it connected directly to the human nervous system.

The stubs of the four main control nerves which fed into her arm, were rerouted to a place on her chest, where they were assured a plentiful blood supply to keep them alive. They were then interfaced into to sensors, which pick up the most delicate electrical activity, and pass that to a computer, which works out what the signals are asking for.

The result is, as Claudia recently said ?They train the arm to understand what it is that I want it to do, I don?t have to think of the entire sequence of movements.?

?They? in this case, being led by the Johns Hopkins University Applied Physics Lab, along with an international team of researchers from across the spectrum.

All work is being co-ordinated with DARPA, the American Defence Advanced Research Projects Agency, who are seeking to replace the lost limbs of soldiers, being blown off in ever-increasing numbers in modern warfare.

The goal is even greater control, with the use of a microchip about half the size of a fingernail that would be placed on the surface of the brain, said Army Col. Geoffrey Ling, program manager of DARPA?s Revolutionising Prosthetics initiative.

This would allow an amputee to play the piano and even write, by tapping into the nervous system, Ling said, adding that primates now testing prosthetic arms are feeding themselves.

The goal of this program is a prosthetic that will be able to function as well as a normal human arm, with strength and dexterity. The system will provide the ability to sense touch, temperature, vibration, the position of the arm and hand relative to other parts of the body, as well as provide a power source that will allow at least 24 hours of normal use.

The mechanical components are being designed and machined carefully, with the benchmark being the necessity to tolerate heat, cold, water, humidity, dust and other elements without breaking down. The goal is also to provide a prosthetic that will last at least 10 years with normal use.

The arm works well enough by pure thought to cook with

Randy Campbell, who lost his arm in an accident in April 2004, is taking part in clinical trials of the arm, developed by DEKA Research, who also has a contract with DARPA. The company?s work with DARPA will wrap up this winter, and will move on to the next phases, which will include approval from the Food and Drug Administration.

Campbell demonstrated by picking up a power drill and drilling a hole, then a screw, into a piece of wood. He also picked up Skittles with his fingers and ate one, but it took a few tries.


Other research, being conducted independently, is also showing very, very promising results. One of the greatest problems with prosthetics, beyond mental control and movement, is dealing with the constant problem of infection, as the prosthetic passes through an open wound in the soft tissues of the body.

As this wound can never close, staying open for the prosthetic, it isa continual worry and source of sickness. That is, it was, before this year.

In June this year, a Belgian German Shepherd dog called Storm, became the first person to be fitted with a prosthetic implant made of technology derived from pioneering work last year at University College London.

The technology is based off of deer antlers, which fit into the bone and stick through the skin with no risk of infection to the animal. There is no open wound, the antler is treated as an extension of the creature. It is obviously desirable to recreate that with prosthetics.

Last year, Dr Paul Unwin, managing director of Stanmore Implants Worldwide, a medical devices company that worked in collaborated with the scientists, said: "The mobility of tissue is a big factor; you don't want the tissue to rip away from the piece of metal, so you need a structure under the skin that will allow the dermal tissues to attach into the metal.

"What we had seen in the deer antlers was that it is very much to do with the structure and shape of the bone, and the porosity of the bone.

"The tissue attaches in with long fibres, and it is like anchors attaching directly into it."

Storm?s implant was successful. A piece of specially shaped and structured rough titanium, mimicking the internal structure of a deer antler, was embedded in his paw stump. Not a complete prosthetic, the titanium, which in future implants would incorporate control wiring inside the metal?s protection, sticks out a little ways from the flesh, acting as an anchoring point to screw the prosthetic onto.

If the prosthetic limb breaks, or is superseded with a new model, just unscrew and detach the old, attach and fasten into place the new. No need to operate, it?s purely a mechanical procedure.

The implant is sealed fully into Storm's body (Credit: BBC)

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