Plastic Prosthetics Help Put Amputees Back in Action

Eagle hand swing

Bob Radocy demonstrates the TRS EAGLE®, a recreational prosthesis with plastic-based joints that store energy from the backswing motion. With this golf model an amputee can duplicate the human biomechanics of a swing.

In the Oscar-nominated feature film 127 Hours rock climber Aron Ralston, played by Oscar nominee James Franco, suffers a rock climbing accident that forces him to amputate his own right arm.

Ralston credits Bob Radocy, the designer of a unique plastic prosthesis and founder of TRS, a Boulder-based prosthetics design and consulting company, with giving him the ability to get back on the mountain. Radocy and his team design unique prosthetics that return amputees to sports and outdoor recreation.

Radocy has been driven by his own experiences as an amputee to create “active prosthetics.” After he lost his left hand in 1971, Radocy used a variety of prosthetics, most of which were made from stainless steel or aircraft aluminum.

Although the all-metal devices were durable, he recalls feeling frustrated by their limitations. “I felt more handicapped by the technology,” he said. In 1977, with degrees in engineering and biology, Radocy began drafting his own device criteria. He refined his designs while he was in graduate school and then founded TRS. As the company grew, Radocy experimented with new materials aiming to develop an “active prosthesis” that could mimic the strength, resilience and flexibility of the human hand. He eventually chose a combination of rigid core plastics and more supple, coated polyurethane for many of the designs. TRS’s Free Flex® and Super Sport ®, multipurpose prosthetic hands for contact athletics, both make use of injection molding technologies and consist of single solid pieces of polyurethane. The solid plastic exterior allows for increased friction and flexibility of grasp and the resulting biofeedback enables amputees to determine how much pressure they exert—something all-metal devices do not offer.

Polyurethane was chosen for the active-use prostheses because the polymer can mimic the characteristics of the human hand such as energy return,  flex and strength in addition to grip and friction, Radocy explains. The Super Sport hand, for example, replicates the palm and is designed to flex and extend like a hand and wrist. “We began to look at polyurethane permaset polymers and temper plastics to create gripping surfaces in the prehensors (hand replacements). Using injection molding, they are easily replaceable, low cost and they give you necessary friction,” says Radocy.

TRS continues to explore new materials and designs that enable amputees to regain their active lives. Radocy has recently started using high-strength synthetic materials to replicate human joints. Introduced in 2009, the TRS EAGLE® golf model is a recreational prosthesis that duplicates human biomechanics and achieves or surpasses human performance.  Plastic-based joints store energy from the backswing motion and release energy at the apex so that prosthetic users can drive further and hit harder. “A person watching from the sidelines wouldn’t know you don’t have a hand,” Radocy says.

“With the right materials that don’t fatigue—synthetic polyurethane in particular—you can create devices that store and return energy when you exert external force to augment and improve the capabilities of the prosthesis.”

“TRS will continue to innovate and improve our products,” says Radocy, with the goal of coming “even closer to doing what actual human limbs can do.