Explained: A prosthetic leg suited for the way Indians sit and walk, adjustable and affordable

The knee

“Western-style” prosthetic legs do not allow for the squat necessary for those using a squat toilet. These devices allow sitting only in the “chair position”, or at 90°.

“If a person tries to sit further down, the knee locks itself. Instead of trying to support the patient in standing up, it will reverse itself… and the person will be forced to sit down,” researcher S Kanagaraj, professor of mechanical engineering at IIT-G, told The Indian Express.

The prosthetic leg Kanagaraj and his team have developed uses a “deep squat mechanism” that helps to prevent this arrest of motion while standing up.
Western-style devices are also unsuitable for cross-legged sitting, and exercise postures in yoga which can be used for rehabilitation. In the new device, an advanced “knee rotation mechanism” facilitates cross-legged sitting.

The ankle

In walking with a prosthetic leg on variable terrain, the hindrance comes from the way the ankle is structured. Whatever ankle joints are available are either rigidly fixed mechanical devices, or advanced ones that use microprocessors, which are expensive. “And maintenance is a bigger problem than affordability,” Kanagaraj said.

The available rigid foot — mechanical foot, rubber foot, or Jaipur foot — allows for no motion beyond a bit of flexing. The joint from IIT-G is not only a little more flexible, allowing a degree of motion, but also has a design suitable for various terrain. The joint is equipped with springs in a configuration similar to the muscular structure that existed before the amputation. Kanagaraj said. “And because there is a little rotation possibility, if there is an angle, something like a ramp, the foot adjusts itself to that particular angle,” he said.

Universal needs

Some needs are not specific to Indian users, such as stability to address the fear of falling at the early stages of using the prosthesis, and walking on staircases once the patient gets used to the device. Also, the needs of the prosthesis vary depending on length of the patient’s leg that remains after the amputation.

The device contains a knee-locking mechanism that can be activated and deactivated depending on varying conditions. It also provides for adjustment of link length, and includes an alignment adjuster mechanism.

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Accessibility

The reason the device will cost in the range of Rs 25,000 is that it integrates all its features into a single design. “There are no multiple mechanical connectors. That’s how we were also able to reduce the number of parts,” Kanagaraj said. “We are also reducing costs in terms of material choices.” The device uses polymers, aluminium alloys and stainless steel for various components.

The team has been working on the project for several years, and Kanagaraj called the present version the “third generation” of the prosthetic leg. “Over the years, we refined the design, we spoke to patients, we understood their needs, we understood the drawbacks of what are available,” he said. He said the device has already been given to several patients and the team is still collecting feedback for further possible refinements.

“We are also in contact with some industries. Let’s say in under a year, it will be available commercially,” Kanagaraj said.