Lots of prosthetic feet are available, but most are built to fit men’s shoes, and none can adjust to a heel more than 2 inches high. That’s less than the average women’s heel height in the US, according to the creators of a new, taller option.
Five mechanical engineering students from Johns Hopkins University and their advisors have developed what would be the first non-custom-made prosthetic foot on the market that can adapt to heels 4 inches or higher.
Some 2,100 American women have lost a leg or foot in military service, and more are entering combat assignments, so the demand for a prosthesis that accommodates a range of shoes is expected to grow. The team—who created what they call the Prominence as their senior project—hope their work can help.
The challenge was daunting: Create a foot that adjusts without a separate tool to a range of heel heights, holds position without slipping, supports up to 250 pounds, weighs less than 3 pounds, and is slender enough to accommodate a woman’s shoe.
The human foot “took thousands of years of evolution to get this way; we have one year to match it,” team member Luke Brown says.
The students struggled to balance the foot’s strength with flexibility, reliability with convenience, and sturdiness with light weight.
They tried a balloon in the heel to give it spring, or “energy return,” as engineers say. That didn’t work. They tried a mousetrap spring, but that didn’t work either. They tried a sideways sandwich of 23 slender titanium plates to form the foot itself, but that was too heavy and not springy. A 20-layer carbon fiber footplate failed a stress test, but a 28-layer version worked, forming the base of the foot.
The students built a heel-adjustment mechanism with two interlocking aluminum disks; it opens and closes with an attached lever at the ankle. For the ankle, they used an off-the-shelf hydraulic unit that enables a smooth gait and flexing at the sole.
Using four types of women’s shoes—including a gold 5.5-inch stiletto—the team had the foot prototype tested by seven people. Three were amputees; four were non-amputees who attached the foot to the bottom of a bulky boot, a bit like walking on stilts.
Alexandra Capellini, a junior who lost her right leg to bone cancer as a child, tried the foot with a flat shoe and liked it.
“I had a good time walking” with it, says Capellini. “It felt stable. … An adjustable ankle is useful in contexts even beyond high heels. Ballet flats, sneakers, boots, and high heels especially, all vary in height, so an adjustable ankle opens up opportunities to wear a variety of shoes.”
One tester recommended a stiffer, longer toe. Another suggested moving the adjustment lever.
The design is still a work in progress. James K. Gilman, a physician and retired Army major general who is executive director of the Johns Hopkins Military and Veterans Health Institute, advised the students. He says it will take time to assess the commercial potential of the Prominence, including the question of whether anything the team created could qualify for a patent.
“I think the final prototype produced showed the way forward,” says Nathan Scott, a senior lecturer in the Whiting School’s Department of Mechanical Engineering, who also advised the student group. “As usual we just need to go around the design and prototyping loop one more time.”
Source: Johns Hopkins University