Prosthetics

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Photo by: Shariff Che'Lah

Prosthetics (pronounced prahs-THEH-tiks) is the branch of medicine that deals with the artificial replacement of a missing body part. A prosthesis (pronounced prahs-THEE-sis) is the general term for the artificial part itself that replaces the body part usually lost to disease or injury. Prosthetics has a long history, and recent design advances that use battery power and new lightweight composite materials are making prostheses better and easier to use.

History

Although nothing can ever fully replace any part of our bodies, most people who have suffered the loss of a body part or who were born missing something that everyone else has and needs—like a foot or a hand—would agree that something is usually better than nothing. People have used all sorts of artificial devices probably from the beginnings of human history to help them compensate for the loss of a limb. Thus in very ancient times, the first and simplest prosthesis may have been a forked tree limb that was used as a crutch to help someone walk whose leg may have been badly damaged or lost in an accident or to a disease.

The known history of prosthetics or designing and making prostheses goes back at least to 300 B.C. , from which time we have evidence of crude devices being made to replace a missing lower leg. These consisted of metal plates being hammered over a wooden core, which was then strapped to the stump of the remaining leg. These very early prostheses were usually made by blacksmiths, armor makers, and other artisans who were skilled at using metal, wood, and leather.

One of the earliest written references to prosthetics is found in a book published in France in 1579. That year, French surgeon Ambroise Paré (1510–1590) published his complete works, part of which described some of the artificial limbs he fitted on his amputees. As a military surgeon, Paré had removed many a soldier's shattered arm or leg, and he eventually began designing and building artificial limbs to help the men who had been maimed. Once Paré's work became better known, others tried to follow his lead. German history tells of the Knight of the Iron Hand who had lost his arm in battle, but who was fitted with an artificial arm that had gears and levers that moved his metal fingers. It is said that he became an even fiercer warrior with his new arm. By the 1700s, metal hooks attached by a wooden or leather shell and leather straps were being use to replace missing hands. In the next century, articulated joints or those that could bend began to replace the stiff solid limb.

Wartime advances

Wartime always pushes surgery beyond its limits, and it is not surprising that most of the advances in prosthetics have taken place during wars. The American Civil War (1861–65) was especially gruesome when it came to maiming healthy young men, and over 30,000 amputations were performed on the Union side alone. A manufacturer in New York priced its wooden socket limbs anywhere from $75 to $150. Most of these prostheses differed little from those of a century before, and it was not until the two twentieth-century world wars that any real progress was made in the design and manufacture of artificial limbs.

During and after World War II (1939–45), newer and lighter materials like plastics and aluminum were joined to newly updated mechanical joints, and for the first time, prostheses became more comfortable and easier to use. With postwar research supported by the U.S. Veteran's Administration, mechanical arms were developed whose hook end could open or close with a shrug of the shoulder. Advances were also made in above-knee and below-knee devices for amputees. Following the Vietnam War during the 1960s and 1970s, a new wave of needy amputees spurred further refinements in prosthetics, and by then electronic control was being introduced.

Many types of prostheses

It should be noted that the term prosthetics does not refer only to the replacement of lost arms or legs. In fact, the word prosthesis includes any artificial body part, and therefore includes everything from a set of false teeth to an artificial breast for women who have undergone a mastectomy (pronounced mass-TEK-tuh-mee) or breast removal. However, the fact that the amputee population in the United States alone ranges somewhere between 400,000 and 1,000,000 makes those in need of a limb predominate. This is especially so since nine out often of these amputations involve the leg from the foot to the knee. Further, three-fourths of these amputations are necessitated by disease, usually cancer or a circulation disease associated with diabetes. The remainder are caused by accidents, with a very small percentage being due to birth defects.

Modern advances in design

An artificial knee joint made out of plastic. (Reproduced by permission of

Photo Researchers, Inc.

)

Given these numbers, it is obvious that there is a real need for new and better prostheses. Fortunately, the beginnings of a major change in design is taking place as composite materials—such as those that combine plastics and carbon fiber—are used more and more. These new materials are much stronger, lighter, and more durable than traditional materials. Silicon-based compounds are used to make artificial arms that are not only softer and more comfortable to wear than the old rigid plastic ones, but are also more real-looking. Often a person can have a mold made of a remaining limb, and a new one is cast to look just like its twin. These new limbs are also adjustable so they can be changed if the person gains weight or increases his or her level of activity. Further, amputees may have shock absorbers in their new knees, which can be made more and more flexible as they become more accustomed to their new leg.

Computers not only assist in the design and manufacture of some of these newer devices, but are being used to revolutionize all manner of prostheses as well. Amazingly, artificial eyes are being researched that will replace a damaged retina and allow certain blind people to see at least basic shapes and movements. Cochlear (pronounced COCK-lee-ur) implants stimulate the auditory nerve with electricity and allow certain deaf people to hear. These do not make sounds louder like hearing aids. Instead, an electrode in the inner ear bypasses the damaged part of the ear and creates a nerve impulse that stimulates the hearing part of the brain.

A typical above-the-knee prosthesis. (Reproduced by permission of

The Gale Group

.)

While some of these devices are astounding in the new or regained capabilities they provide, future systems presently being researched will be truly revolutionary. The goal of today's designers is to build an active device that works very much as our own muscles do. This means that for controlling movement, the ultimate goal is to tap into the nervous system itself and move naturally what are basically artificial muscles. Doing this is very difficult since it means being able to stimulate or detect signals from individual nerve cells. If this type of linkage is ever achieved, humans will be truly melded with a machine.

Besides the difficult problem of connecting with the brain's control system, the other great challenge is providing the power to run these bionic (pronounced by-ON-ik) implants. The energy requirements of any prosthesis are very important, and it appears that for decades to come, batteries of all types will still be used. However, continued battery improvements suggest that future prostheses will use electricity both to power and to control the artificial body part. Today, amputees are able to run races, peddle bicycles, and ski. In England, a man was fitted with the first fully powered electrical shoulder. Continued research and development in prosthetics suggests that life for an amputee will be closer to normal than ever before.