Machine Design

Prosthetics technologies become safer and more reliable

When accidents result in serious injury, amputations are not uncommon. My columns usually focus on factors that lead to injuries with little mention of an injured person’s recovery. However, when there’s an amputation, either at the time of the accident or as part of the injured person’s treatment, prosthetic limbs often bring full or partial function to the injured body part.

I recently spoke with a woman whose leg was amputated many years ago as a result of a bicycling accident. It happened that she had been injured again in an accident that I was investigating, but her amputation was only a peripheral factor in the more-recent accident.

We discussed her artificial leg in great detail because it intrigued me from an engineering standpoint. Her leg used hydraulic and mechanical mechanisms, motion-control devices, and computer control. And it accounts for human factors as well or better than most machines I see in my line of work.

In general, those with prostheses do not appear to be more prone to later accidents. Of course, some amputees using artificial limbs are not able to engage in their previous work or leisure activities or they perform them in a modified way. And, in at least one instance, a long-distance runner’s prosthetic limb improved his speed.

The technologies used in prosthetic limbs continue to evolve into moreuseful and more-reliable devices. Prosthetic-device manufacturers are at the leading edge of a long history of artificial limbs.

Ancient literature and archeological finds show the Greeks, Romans, Egyptians, and ancient Indian societies all fashioned artificial body parts from wood or metal. Prosthetics were either minimally functional decorations meant to hide a missing limb or functional attachments that barely resembled natural body parts.

The technology for replacement limbs advanced little until the 16th century, when doctors developed hinged designs and better ways to attach artificial limbs to natural tissues. Starting in the 1800s, better surgery techniques, including anesthesia and antiseptic practices, let surgeons better prepare limb stumps to accept prostheses and cut amputation-related mortality rates.

Other advances have helped amputees control their artificial limbs. Engineers in the 1800s developed prosthetic arms controlled by the movement of the opposite shoulders via straps or cables. This has evolved to the conversion of nerve signals and voluntary muscle movements into electrical signals that control artificial joints.

Finally, the materials used in making prosthetics have evolved from metals — which were of limited use due to their weight — to wood and on to lightweight engineered plastics and carbon-fiber composites. Computer imaging and modeling also aid in designing and fitting modern artificial limbs.

I’ll discuss the state of the art of prosthetics and its implications for safety and product liability in upcoming columns.

Lanny Berke is a registered professional engineer and Certified Safety Professional involved in forensic engineering since 1972. Got a question about safety? You can reach Lanny at [email protected].

© 2011 Penton Media, Inc.

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