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Davis, California

Thursday, June 13, 2024

Prosthetic limb technology keeps amputees active

When Aron Ralston had to amputate his own right arm to free himself from an 800-pound boulder pinning him to a cliff wall, he thought his outdoor adventures would have to end. Soon, however, the company Hanger Orthotics and Prosthetics was able to fit Ralston with a prosthetic that could support his body weight while hanging or swinging from ledges. An attachment on the end of the arm is an adapted ice ax that he uses for mountaineering and ice climbing.

Such advancements in prosthetic technology are very recent. The first records of prosthetic limbs date back to ancient Greek and Roman times. The Roman general Marcus Sergius lost his arm in battle and famously crafted a prosthetic out of iron to hold his shield.

Since that time, prosthetic limbs have become closer to natural limbs than ever before.

In 1945, the National Academy of Sciences established the Artificial Limb program in response to the surge of World War II veterans who required amputations for their injuries and hoped technology would allow for better prosthetic limbs. New materials, computer models, better surgical techniques and better resources for the rehabilitation of amputees resulted in rapid advancement in prosthetic limb technology.

Modern prosthetic limbs have three major parts: the pylon, the socket and the suspension system. The pylon is the internal frame of the prosthetic limb. Historically, the pylon has been made of metal rods, but recent technological advancements have allowed lighter, carbon-fiber components to form the pylon. The lighter weight material allows the pylon to be covered so that the prosthetic may look more like the amputee’s natural limb.

The socket of the limb is the portion that interfaces with the amputee’s residual limb. In artificial legs, the skin covering the amputated portion is unaccustomed to the high impact force normally received by the foot, the new limb must match up with the residual limb to minimize pain – it’s bad to have the prosthetic bounce against a tender socket.

“[The model] is then modified, shaped and sized to increase pressure on tolerant areas and to decrease pressure on more sensitive areas,” said Scott Cummings, an orthotics and prosthetic practitioner at Next Step Amputee Care Center. “Only when we’ve established the optimal fit do we manufacture the socket out of carbon graphite.”

The suspension system keeps the prosthetic limb attached to the body. The limb may be attached by means of a harness, sleeve or suction.

No matter what technology is used for the prosthetic, rehabilitation is needed afterward for the amputee, particularly in lower-extremity amputations. Julie Gross, a physical therapy clinical specialist for the UC Davis Medical Center, provides physical therapy for amputees working to use their prosthetic limbs.

“It is important to train for getting up off the floor, recovery from a fall, going up and down stairs, walking over grass and walking in crowds,” said Gross. “A lot of the new technology for lower extremities is designed to decrease falls, which is one of the best benefits of microprocessor technology… the [prosthetic] knee reads resistance to prevent a fall, but doesn’t walk for the patient.”

Creating a hand comparable to the natural one is a complicated task as well. The Defense Advanced Research Projects Agency (DARPA) has been working to take prosthetic arms from a hook to a highly capable mechanical hand. One of the new hands has five movable fingers, a rotating thumb, and vibration and temperature sensors.

According to a press release from DARPA scientist Geoffrey Ling, the agency has developed a device that lays on the surface of the brain and captures signals to move arms. The device is about the “half the size of your pinky finger nail.”

As time goes on, both DARPA and private companies around the country hope to increase the durability, sensitivity and motion range of prosthetic limbs. Until then, war veterans and accident victims, diabetes sufferers and developmentally disabled children, continue to test the limits of technology.

AMY STEWART can be reached at science@theaggie.org.


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