If you have an intact body, whilst reading this, stop and think for a minute. How would life change for you, if you lost a hand? How would things change if you lost a foot? If you lost an entire leg or arm? It's a sobering thought. List all the things you do that require two arms, or the ability to walk or run.

How can an amputee hold a frying pan whilst they movethe contents around, take a leisurely stroll, play football, cricket, any competitive sport? Even composing a letter becomes hard if you only have one hand.

Although nothing to date is anywhere near as good as the original flesh and bone, doctors can provide artificial replacements, called prosthesis, for some damaged body parts. In addition to replacing lost functions, prostheses can result in cosmetic improvements for the patient and build self-confidence.

Static Prosthesis

Simple prostheses like peg legs have been around for centuries. This kind of prosthetic, that does not use electronic components to allow it to bend and move, is called a static prosthesis. For example, one variety of artificial arm ends in a pair of hooks rather than a hand. The other end is attached to the remaining portion of the patient's arm, and then to a harness that straps over the shoulders.

By moving the shoulder, the patient can pull on the harness, which in turn pulls on flexible cables to open and close the hooks, allowing the person to grasp objects. There is no sensory feedback in this -no touch, pressure, pain, heat or cold, no sense of grasping, so the only way the user can function, is by watching like a hawk, every minor movement, and correcting visually. Very frustrating and soul-destroying if the person has fully functioning mind-body relations. Picture an amputee with poor hand-eye co-ordination trying to do this…

Dynamic Prosthesis

A dynamic prosthesis is, as the name suggests, much more advanced than a static one. Dynamic prostheses use electronic, and mechanical parts of varying levels of sophistication.

As the nerve and muscle systems within the human body itself, are electro-chemically based, an electronic system can graft onto the body, and tie in with the natural electronics of the nervous system.

For example, an amputee with a myoelectric arm tenses his or her remaining arm muscle. Sensors detect this muscle electricity (myoelectricity) and transmit the signal to the artificial hand, where capacitor and battery arrays increase the level of electrical signal, and open or close the hand.

In more advanced . dynamic prostheses, signals flow from the prosthesis, back to the patient. In the first, crude examples, some prosthetic hands have sensors that can detect heat or cold and transmit that information to electrodes on the patient's skin, which pass that temperature sensation to the central nervous system.

New materials allow artificial feet to press and spring on the ground very much like a real foot. One type of artificial foot transmits electronic information about pressure to amputees, allowing them to balance because they can tell whether their weight is on the toes, heels, or sides of the feet.

BMI and Advanced Dynamic Prosthesis

BMI, or Brain-Machine-Interface, is a new class of dynamic prosthesis, where the prosthetic arm, or leg interfaces directly with the remaining nerve endings in the body, incorporating it directly within the body's periphery nerve network.

With one arm prosthesis, cutting edge at the time of writing, the arm itself hooks directly into the four main nerves which the organic arm uses to connect itself to the central nervous system. Between these four nerve paths, all joint movements and positioning for the natural arm occurs.

Instead of communicating with a missing arm, the stubs of these nerves are re-routed from the arm stub and into the chest, where they can be assured a plentiful blood supply. The ends of these nerves and then fixed 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 net result, is a prosthesis that works off of sub-conscious thought. The brain goes to move a natural arm, but there is no natural arm to move. Instead, the artificial arm picks up on those same signals, and moves itself, exactly as the original would have done.

The arm in the example above, provides no haptics, no tactile, temperature or pain response back to the body. It is strictly one way, radiating from the nervous system, not writing to it. This is mostly because it is not yet possible to include full touch sensors on an artificial arm. However, this is an active area of research, and is unlikely to remain the case for too long.

In Closing

Researchers will continue to improve prosthetic limbs until they are as good, or better than the originals. Some athletes who have received prosthetic parts, already are capable of out-performing their wholly-organic counterparts.

References

First woman fitted with bionic arm, VWN news, http://www.virtualworldlets.net/Archive/IndividualNews.php?News=1659

Are prosthetics Obsolete? Priced out of The Heal Game, VWN staff article, http://www.virtualworldlets.net/Resources/Hosted/Resource.php?
Name=AreProstheticsObsolete

Monkeys Treat Robot Arm as Their Own, BetterHumans.com, link invalid due to site redesign, overview at: http://www.virtualworldlets.net/Archive/IndividualNews.php?News=1047

Resource List: Augmenting the body: Critical Technologies, VWN staff article,
http://www.virtualworldlets.net/Resources/ResourceList.php?ID=16

ASAH - Live Life without Limitations, prosthetic research
http://astepaheadonline.com/