Brace Yourself

Engineers design an ankle device that could prevent falls among the elderly.

September/October 2005

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Brace Yourself

Photo: Linda A. Cicero

The group of 20-something engineers needed to know what it feels like to be 70, getting out of bed in the dark, stumbling toward the bathroom—and taking a fall.

So they stood in buckets of ice water for 10 minutes to simulate losing sensation in their feet. They also shut their eyes, tilted their heads back and spun around in chairs to approximate impaired balance. With each step, they were that much closer to designing a “smart” ankle brace that would help prevent falls by the elderly—injuries that hamper mobility, affect one’s outlook and cost an estimated $26 billion annually.

The six graduate students—Buzzy Bonneau, ’03, MS ’05, Jeremy Dittmer, Surag Mantri, ’03, MS ’03, Tejas Mazmudar, MS ’05, Ryan McDonell, ’05, and Tim Ramsey, ’04, MS ’04—were enrolled in Mechanical Engineering 382: Biomedical Device Design and Evaluation. The Stanford biodesign innovation program had asked Tom Andriacchi, a professor of mechanical engineering and of orthopedic surgery who designed a total knee replacement for arthritis patients in the early 1980s, if his students could come up with a product that would somehow prevent falls.

As the team started out, no idea was too outlandish, says teaching assistant Alfonso Pulido, ’04, MS ’05. They considered wearable harpoons that would shoot into the ceiling as a patient fell and suspend him in midair. Or inflatable air bags that would cushion the impact of a fall. Full-body sumo suits were on the table briefly.

Then Bonneau had dinner with his dad, an orthopedic surgeon. “We were talking and he said, ‘I see all these old people who have no idea what happened when they fell,’” he recalls. “He said they would think their feet were stepping down normally, but their ankles would totally roll and they’d fall over.”

Overnight the project had a focus: proprioception, the awareness of one’s body in relation to the surroundings. As people age, proprioception degrades, along with mobility in their ankle joints. They lose track of how they’re positioning their feet when they’re walking.

Digging into the medical literature, the team found studies that showed that wearing a knee brace had a proprioceptive effect in reducing knee injuries. They bought neoprene braces at Wal-Mart and electronics at RadioShack, and set about building the first prototype for preventing ankle rolls: a sandal with five motors imbedded in the sole.

But the sandal was bulky and no one was convinced that older people would actually wear it. So it was back to the design stage, to come up with something smaller, lighter and less expensive that could be comfortably worn 24 hours a day.

In the Brainstorming Room at the Clark Center, the six students gathered near signs reading “Encourage Wild Ideas” and “Defer Judgment.” As they drew on the whiteboard walls, played with Koosh balls and got their sugar highs from Pez candies, they began to envision an ankle brace with bend sensors and vibrating motors. Positioned near tendons, the motors would deliver a tingling sensation on the side of the ankle to warn the wearer her ankle was rolling—in time to correct the misstep. “The more intense the vibration, the higher the magnitude of your roll,” Mazmudar says. “Which means you’re gonna fall big time.”

The brace they designed is “smart” because of an algorithmic “brain” in the microcontroller that records a history of the wearer’s walking pattern over time. “If there’s a deviation from your past history, it warns you on the side of the ankle that needs to be warned,” Mantri says.

There are still a few dangling wires and the circuit box could be further compressed, but the student engineers have a working model that could be readied for a clinical trial, at a cost of about $1,000. “Right now we need access to a patient population and someone who could manufacture it in large numbers,” says Andriacchi, who heads Stanford’s BioMotion Lab.

Mazmudar thinks there might even be multiple uses for the brace. “I suck at dancing,” he says, “but if someone could teach me how to waltz, and if I made the wrong move, it would vibrate . . .”

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