& Joints

It has been shown that the creation of prosthetic limbs is a science which has been around at least since the days of the Ancient Egyptians.

Prosthetic limbs made of fiber have been found in the wrappings of Egyptian mummies which were probably the creation of the burial priests rather than a functional device. In a Greek myth Pelops, grandson of Zeus, was killed and cooked by his father, Tantalus, to be served to the gods to see if they could differentiate between flesh of man and beast. Demeter, goddess of agriculture ate Pelops' shoulder, but recognizing her error restored him to life and made a prosthetic ivory shoulder [from Prosthetic History Page*].

Creating an artificial limb such as an arm is a very difficult task, even with all of our modern technologies. Not only is there the huge challenge to create a lightweight device which can simulate all of the natural arm's points of movement (shoulder, wrist, and fingers all rotate and bend, lift and lower) but there exists the additional challenge to create a comfortable and effective interface between this machine and a living body. Furthermore, a natural arm is controlled through the nervous system's motor pathways with tremendous precision, and signals from the brain to the muscles are transmitted within fractions of a second. Natural selection has had a long time to develop this brilliant system - one which is not simple to simulate.

The most basic mechanical arms are controlled with cables. These cables are strung around various parts of the body (back, shoulders, etc.), and the arm is moved by complex and quite difficult contortions. According to Dr. Janice Cauwels, 10-15% of amputees actually use cable arms, and that as few as 1% are able to use them successfully.

There is, however, much effort to better utilize modern technology in order to create prosthetic limbs which have more effective, and more natural finctions. One advanced products is a myoelectric arm, such as those made by the Utah Arm* company. Myoelectric prostheses are electric limbs which are controlled by functioning muscles in the body. Small electrodes are placed on the skin over functional muscles. These electrodes measure the electrical activity of the musclus they are over, and through practiced sequences of muscle contractons, one can control the movements of the robotic limb. In the most advanced arms, the motions are not binary (on or off) but can be graded (fast or slow, hard or soft) depending on the input from the controlling muscles.

To compliment these hi-tech arms, companies like Otto Bock* manufacture similarly dexterous hands which are also myoelectrically controlled.

Even as images of the pirate's good-old "peg-leg" still float around our modern sea of media, there have been many technological advancements in the area of prosthetic legs. A CNN* report on the 1996 Paralympic Games describes atheletes' transitions from the wheelchairs to the use of hi-tech prostheses:

In the 1968 games, events such as the shot-put and discus throw were performed only from a wheelchair, and running was unheard of. But now the stiff and heavy wooden legs have been replaced by models with flexible feet that put spring in the step Click here for short movie).

"Actually, the old legs ... you used to be able to hold them and drop them and they would fall right over," explains Paralympic athlete Karen Lewis. But her own foot, she says, would "bounce back up."

The new feet and ankles come in all shapes and sizes. The frames, made of carbon fiber graphite, bend and flex. Bent, the frames store energy; extended, they release it.

It will still be quite a while before we will see prosthetic limbs which can completely make up for the absence of a natural limb. Over time, however, with advances in both the mechanics of the prosthetic limbs themselves, and advances in the connection between the brain and these prostheses, it is hoped that this problem will be conquered.