Affordable prosthetic legs, such as those provided by the International Committee of the Red Cross (ICRC), can restore mobility and independence for users. The ICRC has provided more than 400,000 services to amputees since 1971. Those lower-limb prostheses do not allow for knee rotation, however, which limits common daily actions such as sitting cross-legged, praying and driving.
A project from students at Imperial College London set out to solve that problem. Funded by a £500 IMechE grant, the team aims to improve the everyday lives of users of the transfemoral prosthesis with a new rotational adapter.
The young engineers started by exploring the capabilities of existing adapters, says Prithvi Philip, project lead for the Imperial College Prosthetic Society. Those products often cost hundreds of pounds, yet they are incompatible with the polypropylene prosthetic system provided by the ICRC.
“When I first heard ‘rotational adapter’, in my head it sounds like it just allows free rotation. That’s not the case,” Philip says. “You can press a button that allows you to rotate your leg when you need it to be rotated, such as when you sit cross-legged. And then once you’re done, you can rotate your leg back, then it locks in place.”
Working over several months, the team defined key user needs through co-design with experienced researchers. They prototyped several variants using a combination of 3D printing and CNC machining.
Speaking to Professional Engineering, Philip holds the latest prototype up to the camera to demonstrate how it works. Pressing a small metal button on the adapter, which looks like a white band, he is able to rotate the two halves of the ICRC prosthesis. He then rotates the lower part of the prosthetic leg back into its starting position, and the button clicks into place as it locks.
The team selected the push mechanism for the button as it is easier to use than a pull mechanism, working better under clothes or a prosthetic cosmesis.
Allowing the affordable prostheses to rotate about the knee could make fundamental changes to people’s lives, helping them to engage in communal worship or rejoin the workplace. “Things as simple as tying a shoelace can be made a lot easier by the ability to access your foot,” Philip adds.
A supervisor on the project took a prototype to Cambodia, where it was integrated into a prosthetic leg. Experts provided positive feedback during the field testing.
“Our supervisor spoke to a lot of prosthetists about the design,” Philip says. “They gave us a lot of feedback, which we’re currently working on implementing… that means integrating that feedback, ensuring that it can be designed for injection moulding.”
The adapter also needs to comply with ISO 10328, a standard for the strength of lower-limb prostheses. “There are some other considerations we want to take into account which aren’t in these standards, such as dust ingress and water ingress, which are important considerations in low-to-middle-income countries,” Philip says.
The IMechE grant “has been invaluable in allowing us to prototype with freedom,” says team member Sara Galal. “The funding has enabled us to prototype using materials that would normally be out of reach for student projects, producing a more accurate representation of the final product.
“In addition, it has enabled us to transition further along the development process through increased design iterations, ultimately leading to a more refined and stronger final outcome. Particularly, as a student-run community, it has alleviated students from having to make purchases themselves and supported our development as aspiring engineers.”
After the positive feedback from Cambodia, the young engineers plan to refine the design and scale it for manufacturability.
The students thanked the Cambodian School of Prosthetics and Orthotics, Dr Angus Clark of the Imperial College London Musculoskeletal Mechanics Lab and the team at the Advanced Hackspace for their extensive support throughout the project.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.