Spare Parts: The Uses and Challenges of Prosthetics

by John M. Williams

The War in Iraq is resulting in thousands of individuals with permanent disabilities-at least 8,000 or more thus far-requiring either a prosthetic arm, hip or leg, thereby giving them hope that they will be whole again. According to Pentagon authorities, the number of soldiers requiring a prosthetic will continue to increase as long as the country is engaged in war in the Middle East.

Veterans using prosthetics face new physical and psychological challenges unlike hurdles they have faced before. “To deal with these hurdles veterans should talk to long-time users of prosthetics,” Dr. Hal Allan, a veteran and orthopedic surgeon said.

Not counting the casualties of war, according to a spokesman for the National Rehabilitation Hospital in Washington, DC, more than 1.25 million people in the United States wear a prosthetic device. The causes for prosthetics use vary from injuries to birth defects and diseases such as diabetes and vascular conditions. Aging is the number one cause of a person requiring prosthetics.

Replacement Parts

A prosthesis is an artificial device that replaces a missing limb or other part of the body. Parts of the prosthesis are referred to as components, and they are changing all the time. Each year prosthetic manufacturers design new components, and each component may be similar but have different brand names.

In choosing the correct prosthetic, wearers should know the vocabulary dealing either with a lower or upper limb prosthetic. Doctors, physical therapists, and prosthetists provide advice on particular types of prosthesis. For example:

• Socket is the part of the prosthesis that comes in contact with your limb. It may or may not have an additional part called an insert or liner.

• Suspension fastens the prosthesis to the residual limb.

• Hip is for patients with hip disarticulations and is the mechanical joint that replaces a hip joint.

• Knee is the mechanical joint that replaces your knee joint.

• Shank is the part of the prosthesis between the knee and foot. It can be either a metal pipe covered with foam or a hard, hollow tube.

• Foot/Ankle comes in contact with the ground and provides movement. It may allow movement at the ankle itself, or the foot may be flexible to allow movement.

Challenges

Individuals receiving prosthetics require medical rehabilitation. Rehabilitation helps veterans with physical disabilities, due to trauma or disease, achieve greater independence through high- quality medical care, while helping people with disabilities learn new ways of accomplishing daily activities that are often taken for granted-such as walking, dressing, running, skiing, swimming, feeding oneself, working a computer, or driving a car.

Besides the psychological impact, there are other hurdles facing users of prosthetics. For instance, short users with small body frames should know that weight plays a role in determining the effectiveness of some prosthetics. A motorized, high-tech arm or leg can be difficult to manage, thereby counteracting the benefit of the high-tech performance. Mobility is another challenge. For example, individuals with prosthetic arms and hands can’t use regular wheelchairs, but they can use motorized wheelchairs.

Another hurdle is cost. According to Kevin Carroll, vice president, Prosthetics, Hanger Corp., “The price for a prosthetic device ranges from $3,000 for a body-powered device, such as an arm, to $52,000 for an above-the-knee prosthetic.”

Who pays for these products is another hurdle. Medicare and the VA will each pay for a formulary of prosthetic devices. Still, not all insurance companies pay for all parts, but they usually will pay for a comparable part if there is good justification from a physician. The price to replace a prosthetic device can run fro m $3,000 for an arm to more than $20,000 for an above-the-knee prosthetic replacement using a computer. The average lifespan of a prosthetic device is from three to five years, depending upon the amount of usage.

Maintenance is also a factor to consider. If a new part is less durable, the user must be willing to have regular maintenance.

Upper-Extremity Prostheses

Upper-extremity care includes partial hand, hand, wrist disarticulation, below-elbow, above-elbow, and shoulder disarticulation amputees. Advances in electronics, microchip technology, specialized terminal devices, and lightweight, contoured sockets have brought dramatic improvements to upper-extremity prosthetics.

Prosthetists assist users to discover the combination of componentry to meet their needs. For example, the socket is the critical first component in all upper extremity prosthetic designs. Manufacturers custom- contour each socket to fit the bone, muscle, vascular, and nerve areas of the residual limb. The result is a socket that has total contact and even pressure with all the surfaces of the residual limb. That means greater comfort, increased muscle function, better suspension, and greater range of motion.

The conventional or body-powered prosthesis uses a harness to suspend the arm and fastens around the patient’s upper torso. A cable extends from the harness to a mechanical hand, hook or elbow; exaggerated upper body movements activate the cable, which controls the prosthesis. A different approach is seen in the electrically powered prosthesis where motors can open and close the hand, flex and extend the elbow, or rotate the wrist. This type of prosthesis is often referred to as myoelectric. By contracting muscles in the residual limb, the patient activates the motor in the elbow, wrist or hand. The most advanced myoelectric arms have proportional control hands and flex wrists.

One exciting new technology allows the patient to connect the arm to their computer and use a special software program for technical troubleshooting and to make minor adjustments. It is also possible for the prosthetist to be involved by way of computer modem when more complex analysis and adjustments are necessary.

Lower-Extremity Prostheses

Lower extremity care includes partial foot, below-knee, above-knee, hip disarticulation, knee disarticulations, and hemi-pelvectomy amputees. The goal is to build a comfortable prosthesis based on your goals and lifestyle.

The key component in lower extremity designs is also the socket. It is the critical interface between the amputee and the prosthesis. Older, conventional sockets had a rigid shape that was uncomfortable-even painful-for the patient to wear. Years of research led to a flexible, lightweight socket that is contoured to fit the bone, muscle, vascular, and nerve structures of each patient’s residual limb.

The below-knee socket has varying degrees of flexibility depending on each individual’s needs. A totally flexible brim, total contact fit, and suction suspension provide a degree of comfort.

An important feature of the above-knee socket is that of “containment” of the residual limb. A higher fit is important for rotational stability and side-to-side control of the prosthesis. It also locks the leg into alignment directly beneath the body. Perhaps most importantly, the flexible material and contoured design of the socket make it comfortable to wear.

Many of the advances seen in above-knee prosthetics are applied to patients with hip disarticulation or hemi-pelvectomy amputations. Although these sockets wrap around the entire pelvic area, they are lightweight, flexible, and trimmed out enough to allow greater freedom of movement than previous designs.

Partial foot prosthetics have advanced in design and materials. The slipper-type designs a re fabricated from silicone which simulates human subcutaneous tissue much more accurately than plastics or rubberized epoxy.

The Future

As for the future of prosthetics, new research is speeding the development of brain controlled devices that may soon allow amputees and paraplegics to use their limbs. Within a few short years, these so-called brain-computer interfaces (BCI) may also allow people completely paralyzed by neurode-generative diseases to regain some movement or ability to communicate with those around them.

John M. Williams has been writing about assistive technology for more than 25 years. A sample of his book Assistive Technologies: Creating a Universe of Opportunities for People with Disabilities can be seen at www.atn-ctcf.org.