Prosthetics

Prosthetics is a branch of surgery that is involved in devising and fabricating a prosthesis for a missing or infirm body part. A prosthesis is an artificial part used to restore some amount of normal body function. The classic example of a prosthesis is a false leg or arm to replace one that has been amputated. A diseased heart valve can be removed and replaced by an artificial one.

Artificial body joints have been designed to replace diseased or impaired ones, especially those that have been damaged by osteoarthritis, the most common form of arthritis causing degeneration of the main body joints.

There are a wide range of prosthetic devices for different parts of the body and for internal and external use. Some prosthetic devices are used to improve a body function such as a hearing aid. Others, such as breast implants used after mastectomies, are mainly designed for cosmetic rather than functional purposes. Another example of a cosmetic prosthesis is a glass eye designed to replace an eye lost in surgery. Hip and knee replacements

are examples of internal joint replacements with artificial parts.

Prosthodontics is a branch of dentistry that provides replacements of teeth and other related supportive dental structures. The two main types of replacements are either partial or complete dentures and crowns and bridges, which are placed over existing teeth.

Orthotics is a branch of medicine, allied to prosthetics, that designs devices, such as braces, to correct or control a bone deformity or other anatomical problem that interferes with the correct performance of a part of the body such as the leg, arm, or wrist.

Arthroplasty is a branch of surgical orthopedics in which artificial joints or parts of joints are used to replace joints in the hip, knee, finger, shoulder, and elbow.

Bionics is a field of science that combines mathematics , electronics , biochemistry , and biophysics with the study of living systems to develop innovations in both general and medical technology. It has been responsible for recent major developments in prosthetics. With the application of bionic principles, new prostheses have allowed amputees and those who are paralyzed to walk with feeling by using electronic neuromuscular stimulation. Microprocessors are able to transmit a voltage charge to muscles triggering a reflex response.

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.

Effectiveness

Artificial legs are usually more effective than artificial arms or hands in duplicating the motions of the natural limb. The broad and straight movements of the legs are easier to duplicate than the more intricate and quicker actions of the arms and hands. To compensate for these difficulties, artificial hands and arms with advanced designs that include electronic circuitry allow for a wider range of motion and use. Nerve impulses reaching the stump are transformed to appropriate movements of the prosthesis. Individuals using specialized hand and arm prostheses may have several different ones for different occasions. One could be a glove for social use while another for work might be shaped like a claw or have several different power attachments.

Arthroplasty

Replacing all or part of diseased or degenerated joints through the use of prosthetic joint parts provides the basis for a form of orthopedic surgery known as arthroplasty. Hip replacements were the first arthroplasty operations. They are still being performed with a high rate of success. Other routine joint replacement operations now also include knee joint replacement, finger joint replacement, and the replacement of the shoulder and elbow.

Hip replacement

Hip replacement surgery goes back to the 1930s. By the 1960s three substantial improvements in hip surgery made this procedure both popular and successful. The materials used for the hip prostheses were made from metals and plastics that were strong enough to support the weight brought on the hip and were also self-lubricating. Cements were developed to adhere well to the bone. Extremely antiseptic operating rooms and clothes worn by the operating personnel reduce the danger of infection that accompanies a hip replacement operation.

The hip is the joint between the pelvis and upper end of the femur (thigh bone). It is an example of a ball-and-socket-joint that is subject to several major disorders. The most common disorder is osteoarthritis. Pain and stiffness accompany the movements of the hip. Other types of arthritic disorders can cause similar malfunction. Fracture of the hip often occurs with the elderly, who may be prone to falls. In the case of extreme trauma there may be a dislocation of the hip, which is rare but may occur in such mishaps as an automobile accident.

Hip replacements are surgical procedures in which either part or all of the hip joint is replaced with artificial parts. In the operation, the hip joint is exposed from around the surrounding fat and muscle tissue . The thigh bone (femur) and pelvis is prepared to accept the two component parts for the replacement to the natural hip joint. The components consist of a metal shaft and ball as one unit replacing the shaft of the thigh bone with its natural ball and a socket that is made either from metal or plastic. The new socket receives the shaft and ball after it is cemented into the pelvis. These parts are bound into place by a special cement into the surrounding bone. After the new ball is attached to the socket, the muscles and tendons are stitched back into place and the incision is closed.

Recently, a robot has been devised that can drill a hole in the femur much more accurately than a surgeon can. The robot's precise hole can hold the prosthesis much better, thus extending the life of the hip replacement. A surgeon can be as much as 30% off in his drilling. When that happens, only twenty percent of the implant comes in contact with the bone, leaving wide gaps around the prosthesis. Use of the surgical robot brings 96% percent of the implant in contact with the bone and gaps were reduced from 0.15-0.02 in (4.0-0.5 mm). This technology is still in an early state of development.

Recovery

It takes about a week for the cement to become fixed. In that time the patient is expected not to engage in movements that would dislocate the new joint. They are given special advice on how to sleep (on their backs) and told not to cross their legs. Care must be exerted during this period in conducting such movements as getting in and out of a bathtub. Recent research indicates that when the candidates for hip replacement surgery perform the rehabilitation exercise before the surgery the rate of recovery time is significantly reduced.

While hip joint replacements have proven to be very successful there is a problem of the cement loosening after an extended period of time. Research is being done for designs that do not rely as much on the use of cements. Hip replacements are usually not advised for those under 50 because of the unknown long-term effects, especially with the use of cement. Younger patients, however, are now considering cementless artificial hips as an alternative to the conventional procedures that do use cement. The newer technique that does not use cement takes longer, but some orthopedists believe the procedure offers better long-term results.

These newer types of hip replacements are of special interest to athletes in need of relief from hip pain. Athlete Bo Jackson returned to play with the Chicago White Sox after an operation that replaced his left hip.

Knee joint replacement

Large hinges were used in early examples of knee joint replacements. Operations for knee joint replacement, today, are implants within the joint using metal and plastic parts used to cover the worn parts of cartilage in the joint. The objective is to save as much of the joint as possible. This procedure is used mostly for elderly patients suffering from osteoarthritis or rheumatoid arthritis. Younger people are usually not advised to have a knee prosthesis because it reduces the range of movement for the knee and usually will not withstand the strains of vigorous use.

In the operation to install the knee prosthesis the flat undersurfaces of the knee joint are exposed. The lower end of the femur (thigh bone) is smoothed down to accept the prosthesis and then holes are drilled to fasten it. Likewise, the upper end of the tibia (leg bone) is prepared and the back part of the patella (knee cap) is prepared to accept the patellar component of the prosthesis. The parts are then cemented and tested to see if the joint movements are proper. The knee prosthesis consists of the femoral component and the tibial component along with the patella component.

The main purpose of the knee joint replacement procedure is to reduce pain and to restore some movement to the joint. The outcome of the operation lacks certainty and the duration of the prosthesis is limited. Research continues to find better cements and materials for the joints as well as designs that come closer to the actual joint.

Wrist and finger implants

The wrist is a complex joint consisting of eight bones and lies between the lower forearm and the hand. In the United States there are about 2,000 wrist implants and 7,000 hand and finger implants each year. There have been studies that indicate these implants may have damaging effects since they use silicone materials to replace damaged bone. The silicone particles may travel to nearby tissues, causing an immune response that ultimately damages surrounding bone. Many patients require additional surgery as a result. Some physicians maintain that the implants can cause more damage to the healthy bone than the harm done by the disease itself. So far the FDA has not decided to investigate these implants.

Breast implants

Due to the prevalence of breast cancer in women, which necessitates the removal of one or more breasts, breast reconstruction surgery is a common procedure. This involves the implantation of a sac filled with silicone gel or saline. Breast augmentation is also practiced as a purely cosmetic procedure by women who wish to enlarge their breasts.

The use of silicone in this procedure has become controversial. Silicone is a polymer , that is, a silicon compound united with organic compounds. While silicone rubbers have been used for many years, in 1992 the FDA asked that the use of silicone for breast implants in cosmetic surgery be suspended in order to have time to study the complaints against silicone. There have been reports of autoimmune reactions caused by implanted silicone. Some cases showed permanent sores and lumps arising after the implant. There was also a fear expressed by researchers of the possibility that silicone might migrate to the lungs, causing death. Although subsequent testing cast doubt on the actual negative side effects of silicone implants, they have been replaced in most cases by implants using saline solution .

Implanted prosthetic materials

Heart valve implants and plastic surgery for the face or in smoothing wrinkles employ the use of silicone materials as well. The FDA continues to study other high-risk medical prostheses. These include inflatable penile implants, testicular implants, heart-bypass pumps, cranial stimulators, and saline-filled breast implants.

Heart transplants

Heart disease is one of the most common killers of middle-aged men and women. Artificial heart valves are now commonly transplanted into living hearts to replace malfunctioning valves. However, this procedure only treats one type of heart malfunction. Many types of artificial heart have been tested, with the hope of replacing the entire organ with an electro-mechanical substitute. This technique attracted a great deal of publicity in the early 1980's, when a few patients received permanent mechanical replacement hearts. Unfortunately, these patients lived only a short time after receiving the transplants. Though research continues into smaller, more reliable devices that do not trigger rejection from the body's auto-immune system, they are still considered temporary expedients that allow a patient to remain alive until a suitable human heart is available for transplantation. Even then, artificial hearts and Vascular Aid Devices (VAD) are used in only the more desperate cases, since infection and rejection can cause further damage, which would reduce the chances of a successful human heart transplant, causing the patient to be removed from the transplant list.

Bionics

The field of prosthetics has received a major impetus from the development of bionics. In bionics, engineering problems are solved by studying the properties of biological systems. For example, studying the swimming movements of fish and the flight of birds give the bionics engineer clues on how to solve problems in jet and rocket propulsion. Problems of conservation of energy in engineering are studied in relation to other biological examples.

Bionics is an outgrowth of the field of study known as cybernetics . The concern of cybernetics is to relate the way machines communicate, are controlled, and acquire information to similar processes in life systems. Bionics, like cybernetics, depends on the understanding of physiology , biochemistry, and both the physical and mechanical properties of living things. The bionic scientist must be prepared to apply mathematics, physics , and electronic engineering for the formulations of the interfaces between living and mechanical systems.

Bionics grew out of a concept known as the general-systems theory. Nicholas Rashevsky, a Russian-American scientist, was the first to develop a correlation between the workings of the central nervous system and mathematical models. After his initial studies, other physicists and engineers entered the field of bionics. They have studied the way in which visual images are established within biological visual systems. From these investigations technologically advanced cameras, television , and optical-recognition systems have emerged. Those who studied biological auditory systems were able to devise major improvements in radio transmitters and receivers.

Along with all of its other applications, bionics has been a major force in the development of prosthetics. The field of artificial organ transplantation owes its development to bionics. Artificial limbs—arms and legs—can now be electronically controlled by an electronic process that recognizes various patterns of electrical movement. Complicated movements of the prosthesis can be brought about by microcircuits that detect the patterns of electrical impulses within the tissue of the surrounding muscle as it is expressed on the outer skin. Electronic motors then carry the prosthesis to its task.

Other prosthetic devices employing bionic principles allow some of the blind to regain a sense of sight by transmitting nerve impulses around the damaged neural pathways to ones that are still capable of transmitting signals. Hearing aids are another example of prosthetic devices that have benefited from bionic research.

Resources

books

Delisa, Joel A., et al. Rehabilitation Medicine. Philadelphia: Lippincott, 1993.

Sanders, Gloria T. Amputation Prosthetics. F.A. Davis Company, Philadelphia, PA., 1986.

Wilson, A. Bennet, Jr. "History of Amputation Surgery and Prosthetics." Atlas of Limb Prosthetics: Surgery and Prosthetic Principles. Americal Academy of Orthopedic Surgeons, C.V. Mosby Company, St. Louis, MO., 1981

periodicals

Jones, Stella. "Making Artificial Organs Work." TechnologyReview 97 (September 1994): 32-41.

Padula, Patricia A., and Lawrence W. Friedmann. "Acquired Amputation and Prostheses Before the Sixteenth Century." The Journal of Vascular Disease (February 1987).

Randall, Teri. "Silicone Implants for Hand and Wrist." TheJournal of the American Medical Association 268. (July 1, 1992): 13-16.

Romm, Sharon. "Arms by Design: From Antiquity to the Renaissance." Plastic and Reconstructive Surgery (July 1988).

Sterling, Bruce. "The Artificial Body." The Magazine of Fantasy and Science Fiction (October-November 1994): 138-147

Jordan P. Richman

KEY TERMS

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Autoimmune reactions

—The use of certain substances in prosthetic devices may trigger the production of antibodies from the immune system causing adverse effects.

Ball and socket joint

—A type of joint that allows the widest range of movement found in the hip and shoulder joint.

Bionics

—A new field of science that combines engineering with biology.

FDA

—The Unites States Federal Drug Administration; oversees and regulates the introduction of new drug products into the medical marketplace.

Femur

—The thigh bone which is the site for the implantation of hip and knee prostheses.

Myoelectric control

—The electrical stimulation of prosthetic devices from the surrounding muscle tissue.

Osteoarthritis

—The most common form of arthritis which is responsible for the degeneration of the cartilage in bone joints.

Silicone

—A controversial substance that has been used in breast and other types of implants. It has moved from a low-risk prosthetic material to a high-risk category by the FDA.

Socket

—The part of a limb prosthesis that fits over the stump of the amputated limb.

Tibia

—The leg bone.