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Prosthetics

Artificial Limbs

Artificial limbs have been used for more than 2,000 years. The earliest known artificial limb was a leg made of metal plates surrounding a wooden core. It was not, however, until the World War II that the major developments in artificial limbs occurred. In this period, much progress was made by surgeons and prosthetic makers to help wounded soldiers adjust to civilian life with the help of newly designed and effective prostheses.

War has been the greatest impetus for advances in prosthetic design. For centuries, amputation was the most common therapy for traumatic injuries to a soldier's extremities. But until the middle of the nineteenth century, most patients died of infection due to the unsanitary surgical techniques of the time, leaving little room for advances in prosthetic technology for the survivors. Amputated hands were often replaced by simple hooks, and amputated legs by wooden pegs topped with open saddle-like sockets. Since the second world war, improvements in low-weight, high-strength materials and techniques for fitting and shaping artificial limbs have made these types of prosthesis much more useful and comfortable for the patients.

Candidates for artificial limbs to replace legs, feet, arms, and hands are those who have either lost the limb as a result of surgical amputation or were born with an impaired or missing limb. The process of preparing a patient for an artificial limb begins with the amputation. The amputating surgeon considers the best design for the stump or remaining part of the limb. After the wound has healed, a prosthetist chooses an artificial limb or prosthesis that will either have to be a weight-bearing replacement, or an arm and hand prosthesis that will have to manage a number of different movements.

There are several criteria of acceptability for limb prostheses. They must be able to approximate the function of the lost limb. They should be light, comfortable to wear, and easy to put on and take off. Substitute limbs should also have a natural appearance.

Pre-constructed artificial limbs are available for ready use. Going to a prosthetist, one who specializes in constructing and fitting artificial limbs, gives better results in adjusting the prosthesis to the individual's requirements. Recent technological developments have enabled prosthetists to add to artificial joints made from plastic, carbon fiber, or other materials that enable the wearer to include a variety of motions to the limb prosthesis. These motions include rotation around the joint and counter pressures that stabilize a weight bearing joint, like the knee, or they may even be able to control the length of the stride of an artificial leg.

The prosthetist first makes a mold from the stump of the missing limb. This mold forms the basis for the artificial limb and holds the top of the prosthesis comfortably on the stump. The socket can be constructed from various materials, such as leather, plastic, or wood and is attached to the stump by a variety of means. The leg prosthesis socket in which the residual limb fits is aligned with the feet, ankles, and knees for each individual. Improvements have been made in foot design to make them more responsive and in designing comfortable and flexible sockets. Materials such as carbon graphite, titanium, and flexible thermoplastics have permitted great advances in leg prostheses. Applications of electronic technology allows for a wider range of sensory feedback and control of artificial knee swing and stance.

Extending from the socket is the strut, which is the artificial replacement of the thigh, lower leg, upper arm, or forearm. Different types of material can go into the making of the strut. The strut is covered by foam rubber pressed into the shape of the limb it is replacing. The outer covering for the finished prosthesis can be made from different types of materials, such as wood, leather, or metal.

The aerospace industry has provided materials and electronic technology for developing prosthetic devices that can approximate movements of the muscles. Hand and arm replacements are usually operated by voluntary muscle control from the opposite shoulder through cables that connect from the shoulder harness to the artificial hand or hook, called the terminal device. Arm prostheses may also be operated by myoelectric control. (Myo means muscle.) The electrochemical activity of key arm muscles is received by electrodes in the prosthesis and is then transmitted to a motor that operates the prosthesis. Although this branch of prosthetics is still in its infancy, there is great hope that electronic controls will result in much more articulate hand movement, and will eventually replace cables that can simply open or close a hook or artificial hand.

Ironically, progress in prosthetic technology has been slowed by advanced surgical techniques, which have made amputation as a result of traumatic injury much more rare. Orthopedic surgeons can now repair limbs that would have once been routinely amputated. Severed limbs can even be re-attached in many cases.

Additional topics

Science EncyclopediaScience & Philosophy: Propagation to Quantum electrodynamics (QED)Prosthetics - Artificial Limbs, Effectiveness, Hip Replacement, Recovery, Knee Joint Replacement, Wrist And Finger Implants - Arthroplasty, Implanted prosthetic materials