Prosthetics

Summary

Prosthetics is the branch of medicine focused on replacing of missing body parts with artificial substitutes so that an individual can function and appear more natural. Prostheses are commonly used to replace hands, arms, legs, and feet; however, other prosthetic devices developed to improve one's quality of life are heart valves, pacemakers, and components of the ear. Some prosthetic devices, including eye and breast implants, are developed primarily for cosmetic reasons. Several healthcare professions work together as a team in this process, and teams include a surgeon, a nurse, a prosthetist, and physical and occupational therapists.

Definition and Basic Principles

“Prosthetics” is the science of developing and fitting substitute body parts. This branch of medicine is devoted to assisting patients in regaining as much function as possible after they have lost a body part from trauma, a congenital disability, or illness. Replacing a limb or other impaired or lost body part involves fitting an individual with an artificial leg, arm, or other body part to allow them to perform the activities of daily living.

A “prosthesis” is a device that replaces a missing body part or augments a partial one; an individual who measures, fits, and modifies the prosthesis is referred to as the “prosthetist.” Legs, arms, feet, and hands are the most commonly known artificial devices.

Although closely related to the field of prosthetics, the term “orthotics” is not identical in meaning. Orthotics usually focuses on the management of impairment, but the treatment may be more temporary, whereas prosthetics concerns permanent artificial replacements of body parts. An orthotist designs and fits surgical appliances; this process is referred to as “orthosis.” Orthotic devices include braces, neck collars, and splints. Such devices are designed to support the patient's limbs or spine while relieving pain and helping movement. They also may be designed to restrict movement and provide an environment of protection and healing.

Background and History

The use of prosthetic devices can be traced back to sixteenth-century knights. A German knight known as Götz of the Iron Hand may have been the first to apply the science of prosthetics. He developed and used an appliance with movable fingers to help him hold a sword (hence his nickname).

Until the twentieth century, most prosthetic devices were made of wood, but because of the large number of amputees produced by World Wars I and II, these devices began to be made of metals and fibers. The devices were designed to increase function and, therefore, incorporated mechanical devices and elastic materials to allow individuals to move their artificial limbs more effectively and easily.

In the late twentieth and early twenty-first centuries, advances in biomechanics and bioengineering resulted in prosthetic devices such as hydraulic knees and computer-programmable hands that sense the slightest muscle movement. Such technology has led to advances in prosthetic devices for other body parts, including the heart and the ear.

How It Works

Prosthetics is often defined as a branch of surgery involving a team approach comprising such professionals as surgeons, nurses, prosthetists, physical and occupational therapists, prosthetic technicians and assistants, rehabilitation counselors, and social workers. By combining medical science with technology, rehabilitation engineering assists in designing and developing devices to meet each individual's needs.

Interaction with the patient begins well before any surgery, with the physician determining if replacement of the natural body part is required. If a surgical procedure such as amputation is required, the physician, nurse, and social workers must prepare the patient emotionally and physically. The prosthetist, physician, and physical therapist consult with the patient to determine the size, shape, and material most appropriate for the appropriate device. The physical therapist evaluates factors such as strength and ability to wear the prosthesis and works with the patient to increase physical strength as appropriate for the device involved.

Prosthetists and technicians work with their hands and high-tech machinery to make molds or casts of the amputated area to create the desired device. This process may include casting molds, using sewing machines, and heating plastics in a special oven. Rehabilitation engineers apply their expertise as well; for example, depending on the needs of the individual patient, they may suggest a prosthetic foot that offers a more natural spring to help push off from the floor from a standing start, or they may help design a prosthetic knee to facilitate stair climbing that avoids rubbing the foot on the steps (which could result in a fall).

Most prosthetists and related healthcare team members often work in a combination of environments inspected and regulated by the American Board for Certification in Orthotics, Prosthetics, and Pedorthics. Later stages of rehabilitation engage an occupational therapist, who focuses on helping the patient complete everyday tasks independently with the new prosthesis and suggests activities to strengthen weakened muscles.

Applications and Products

The products of prosthetics are primarily the physical devices used to replace lost body parts. The most common prosthetic devices replace limbs, but other, less familiar devices are also considered to be prostheses. The users of these products include a broad range of individuals, from children born with missing limbs to military personnel who have been injured during battle. The largest population of amputees in the United States are those individuals who have lost a limb from either diabetes or peripheral vascular disease. Trauma victims, such as those who have experienced motor vehicular accidents, make up another group of users since accidents account for many lost limbs.

Prosthetic Limbs. Over the years, prosthetic limbs consisted of combinations of springs and hinges to increase motion and function. Prosthetic limbs use a socket to fit over the remaining part of the limb and provide a link between the body and the prosthesis. Additional straps and belts are often used to attach the device to the body, with soft, socklike material used in between to protect the area of contact from excessive pressure and friction. The main body of the prosthesis is often made from material such as carbon fiber, popular for its light weight, strength, and durability. These properties require less exertion of effort from the patient, and the device appears more natural.

Prosthetic legs are generally of two types: transtibial and transfemoral. A transtibial prosthesis replaces the leg below the knee, which allows the knee joint to remain functional. A transfemoral prosthesis replaces the entire leg, including above the knee joint. Traditionally, the force needed to move either type of device has come from the patient's remaining muscles, including the momentum from using their entire body. Newer technology has brought the use of myoelectric limbs, which respond by converting muscle movement to an electric signal to move the device. This technology has allowed patients with leg and arm prostheses to have better control of the limb.

Prosthetic devices for the hip are made from materials similar to those used for prosthetic legs to provide strength, comfort, and support. A prosthetic hip joint is designed to support and link the patient to the prosthetic leg using a socket fitted to the body's torso and pelvis using a system of straps. Some artificial hip joints use a roller system to convey forces from the socket directly to the prosthetic leg.

Prosthetic arms and hands have advanced, using stronger and lighter materials that also look more like skin. The biomechanics of these devices have improved: Once anchored to the opposite shoulder with straps across the back, these devices have come to use electrical signals from the patient's nearby muscles to move specific fingers. By 2015, the online nonprofit group e-NABLE, founded two years earlier, began making affordable prosthetic hands—mainly for children—using 3-D printers. After getting measurements using an online tool to custom make each hand, the plans are downloaded into the machines and the prosthesis is made using materials of relatively little cost that can be pieced together by the recipient. A team of e-NABLE community members designed a kinetic hand in 2020 by using computer-aided design (CAD) software like Geomagic Freeform for virtual sculpting and Solidworks, a computer-aided engineering (CAE) platform. A technique known as targeted muscle reinnervation (TMR), whereby the arm or hand will respond to signals from the brain to specific remaining muscles, has also gained promise. Patients can potentially manipulate a prosthetic hand as naturally as they once could move their own hand. In 2015, this procedure, once only experimental, was made available to the public at facilities such as the Rehabilitation Institute of Chicago and the Johns Hopkins Hospital. The TMR procedure helps prevent neuroma formation that causes phantom pain (post-amputation painful sensations from the missing part or limb). It can provide better control in patients with myoelectric prostheses, especially in upper limb amputees and functional prostheses used in hand and finger injuries.

Prosthetic applications for the foot have been primarily rigid in design, with little, if any, movement. Traditionally, prosthetic feet were made from leather, metal, plastic, or a combination of such materials. Modern foot prostheses have improved, with computer-controlled components designed to handle the user's weight and the return of their momentum. Such products have been reported to be comfortable enough for participation in recreational sports. Further improvements have occurred with the use of carbon fiber, compression springs, and telescoping tubes that help the prosthetic foot move more naturally without inducing pain or discomfort.

Nonlimb Prosthetic Devices. Other prosthetic devices include artificial eyes, breasts, heart valves, and pacemakers. The body's natural heart valve may need to be surgically replaced if it no longer functions properly because of disease, aging, or a congenital disability. This vital prosthetic heart component is made from plastic, metal, or pig tissue. Calcification of the prosthetic heart valves is the major cause of product problems, and efforts have been aimed at constructing artificial valves with surfaces that resist calcification. Technological advancements in the durability of the tissue heart valves are also an area of research and could be more applicable to younger patients.

Prosthetic eyes are traditionally made from hard materials such as acrylic, gold, ceramics, and glass. When an individual loses an eye, it is replaced with a temporary implant positioned toward the back of the eye socket to allow proper room for the prosthetic eye. Using of an impression, a wax model is made, followed by a mold for casting the prosthetic eye. Components of the eye, such as the pupil and the iris, are painted on a round plastic base and eventually inserted on the prosthetic eye. Some prosthetic eyes can even be designed to allow for the attachment of eye muscles. One of the trends in design is to develop an ocular system that allows for more natural movement.

A popular product for women who have had a mastectomy, prosthetic breasts are made of various materials, including lightweight silicone, soft gel, and a variety of fabrics. Breast prosthetics are often engineered using a cast of the body shape and other parameters. The prosthetic breast needs to be lightweight to avoid strain on the back and shoulders. Cosmetics—shape and contour—are a concern in the design and development of this form of prosthesis, as is comfort. For example, one breast prosthesis has at its center a climate control pad made of a soft gel that absorbs body heat, creating a cooling sensation. Future breast prostheses are expected to be developed with some type of climate-control technology.

Pacemakers are a complex form of prosthetic devices whose design and development require high-tech electric and computer expertise. These units are manufactured by the biomedical industry and have progressed significantly to keep up with advances in medicine. Originally stimulating the heart to beat at a standard rate of around seventy beats per minute, pacemakers can now interpret signals from the patient to change the heart rate. The latest device can take the electrical impulses from the heart's natural pacemaker, the sinoatrial node, and increase the heart rate during activity as needed.

Ear components, specifically the cochlea, are less well-known but are gaining popularity. Artificial cochleas can now duplicate the function of converting sound waves into electronic chemical impulses.

Neuroprosthetics. Neuroprosthetics, a subspecialty of prosthetics, aims to integrate body, mind, and machine. One example is the development of a system that can decipher brain waves and translate them into computer commands. A young science, this specialty promises to allow people with quadriplegia to gain sufficient function to operate household electric appliances and computers by using their thoughts transmitted by an implant.

Tissue Engineering. The concept of tissue engineering to complement prosthetics promises to play a key role in twenty-first-century prosthetic devices. Surgical techniques are being developed that could lengthen the bone in a residual limb to fit artificial limbs more effectively. Problems associated with anchoring methods can be solved with tissue engineering by developing the technology of attaching prosthetic legs to a titanium bolt directly in the bone, a process known as osseointegration. Research in nanoscale biocompatible 3-D printed bone substitutes can improve materials used in the prosthetic industry.

Careers and Course Work

The need for prosthetists, prosthetics assistants, and technicians is expected to increase as a result of an aging population, increases in obesity and diabetes, and the medical demands of war-related amputees.

A Bachelor's degree in prosthetics is usually required from a program accredited by the American Board for Certification in Orthotics, Prosthetics, and Pedorthics (ABC). Following a period of supervised clinical internship, college graduates are eligible to take examinations given by its governing board. Another route to the profession has been designed for other members of the healthcare team, such as surgeons, nurses, and physical therapists. These professionals may receive training in prosthetics while studying to achieve certification in their respective specialties.

Another avenue is to become certified by earning an associate degree in any field, then completing a certificate program in orthotics and prosthetics, followed by working for four years in the field and eventually passing certification exams. Programs for prosthetics assistants and technicians range from six months to two years of study, and internships are offered by the American Academy of Orthotics and Prosthetics, which also provides continuing education courses and forums so those in the prosthetics industry can learn about new developments.

Because some patients will require both prosthetic devices and orthotics, many programs offer degrees and certificates in both disciplines. Individuals with education and experience in both disciplines will possess much more knowledge and therefore be more employable, compared with those with degrees or certificates in only one of the disciplines. Various sectors that recruit prosthetists include the federal government, medical equipment suppliers, and ambulatory service providers.

Social Context and Future Prospects

Prosthetic devices can restore independence to people who have lost limbs or function through the impairment of body parts. With a prosthesis, people can return to such fundamental activities as walking, writing with a pen, feeding themselves with a fork or spoon, receiving a handshake, holding a newborn, and even performing sports. Such abilities, which most people take for granted, are dramatic to the person who has lost function and may mean the difference between independent living and institutionalization. With rising amputations, research in robotics and myoelectric wireless sensors can improve control, comfort, and aesthetics of prostheses, restoring self-esteem and body image.

As the twenty-first century progressed, innovations continued to be made in prosthetics, improving the quality of life for patients and extending their abilities. Patients could better control their artificial limbs through developing technologies, like myoelectric control and Targeted Muscle Reinnervation. The medical and scientific community also made strides in the sensory perception of prosthetics, allowing patients to feel the physical touch of others or changes in temperature. New prosthetic materials were also being developed, and the use of virtual reality and artificial intelligence in rehabilitation grew. 

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