Amputees: Sensory and Unavoidable Limb Loss, Prosthetic Materials

by Food and Drug Administration (FDA)

(Page 2 of 3)

Sensory Loss

Another danger with diabetes is a deadening of the nerves in the extremities. John F. Glass, a biologist with FDA's pacing and neurological devices branch, said there are now a variety of devices that measure sensory loss in the affected limbs. In a patient with diabetes, loss of sensation because of nerve damage signals a need for diligence. Even minor injuries, undetected because the feeling is gone and thus left untreated, can become infected easily and lead to gangrene.

"If you're aware of sensory loss, you want to keep a close watch on it," Glass said. "There's a range of measurement devices, from those that detect general loss of sensation, to those that assess the specific degree of sensory loss, or that can quantify sensitivity to pressure or temperature."

Many of the devices are easy-to-use mechanical implements with no significant health risk to patients. One of the simplest is a hand-held device that looks like an old typewriter eraser with thin wires attached to it. The wires are placed on the toes or fingertips to see if there is tactile sensitivity.

Such simple devices are typically not reviewed by FDA before they are made available to the public. They are intended for use by the patient for monitoring only, not self-diagnosis.

"Loss of sensation in an extremity could indicate a lot of other conditions or disorders, so we would encourage the patient to see a physician immediately for a complete physical examination," Glass said.

Unavoidable Limb Loss

Precautions such as Glass advocates can often delay the progression of the disease. Sometimes, though, the loss of a limb is unavoidable. In those cases, physical therapy starts a day or two after surgery. Since more than 9 out of 10 amputations involve one or both legs, physical therapy usually involves the use of parallel bars, and later a walker or crutches. Part of the training involves how to fall and get up safely.

There are other adjustments as well. Barr said the loss of both legs, and covering the stumps with plastic, means his body has become much less effective at cooling itself, so he has to be on the lookout for hyperthermia. And he learned other tricks to cope, as well.

"I'm constantly on the move, never standing still, always readjusting my balance even when I'm staying in one place, because I don't want one particular area on the stump to get sore," Barr said.

Until recently, patients were not fitted with an artificial limb for four to eight weeks after surgery, but new techniques allow the use of a protective foam over a sterile bandage, and the prosthesis can be fit as soon as the day following surgery.

New Prosthetic Materials

For centuries, wood and leather were the only materials for prostheses, but today's physical therapist has a much wider range available, including advanced plastics and carbon fiber, which are much stronger and lighter and more durable.

"The industry is really moving towards composite materials, because they're lighter in weight, easier to work with, and more durable," said Douglas McCormack, vice president of the Amputee Coalition of America.

Silicone-based compounds used to make prosthetic arms, for instance, give the appearance of real skin, unlike the rigid plastic or metal limbs of years ago, and they are more comfortable for the person wearing them. Women can get prosthetic feet with life-like toes for when they wear sandals; men can get legs with the appearance of hair.

But even materials that work out in one application might not work in another.

"We tested a silicone foot at one point. On a machine it was subjected to 300 pounds of stress for a million cycles, and it didn't have any problems. But an amputee broke it within a few minutes. It really surprised us. Torque and other stresses can fatigue the material quickly," said Sabolich's Ortega. "You'd be amazed at the toll that a human body puts on even the strongest material."

New computer programs better determine where and what the forces are. But it's not just a question of choosing a material that will withstand those forces.

"With some of the new materials being developed, we could make a foot to take any of the pressures that the human body will give it," Ortega said. "The problem is it might not have any springiness. You give up flexibility for strength. You have to balance all the considerations in a prosthetic."

Prostheses are typically sold as components, so that someone who has an above-the-knee amputation would be able to choose leg, knee and foot units, often from different manufacturers, depending on their individual needs.

Most of the units are adjustable. Shock absorbers in knees, for instance, can be made more flexible as a person gains controls over the artificial leg. Ankles can be adjusted to the weight and activity level of the patient.

Arm amputees today can choose between prostheses that are powered by a harness and cable attached to the residual limb, or externally powered devices. Powered arms can be controlled by switches mounted inside or outside the socket, that the patient can activate by flexing certain muscle groups.

About the Author

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