Ordinarily, prosthetic legs have ankle joints that are passive, moving only in response to pressure exerted by the user. As a result, walking up stairs or over uneven ground can be difficult. A new "smart" prosthetic ankle, however, automatically adjusts the angle of the foot according to what the user is doing.

Developed by a team at Nashville's Vanderbilt University, the prototype device contains a motor, actuator, sensors and microchip. Utilizing these, it's able to ascertain what sort of activity the user is currently performing, allowing it to change the angle of the foot so that it's in the correct orientation at all times. This means that if the user is climbing stairs, for example, the ankle automatically raises the front of the leading foot, so that it doesn't get caught on the edge of the next step.

"Essentially, the ankle uses its on-board sensors (that sense load and motion) to determine how the user is interacting with the environment," Ph.D student Harrison Bartlett tells us. "The ankle then determines what the user is doing through those sensors and adapts its behavior accordingly."

Additionally, whereas users of traditional prosthetic legs tend to stick with one type of shoe that they're used to, the Vanderbilt ankle adapts to and compensates for the differences between various shoe types.

"Our prosthetic ankle is intelligent, so you can wear a dress shoe, a running shoe, a flat – whatever you'd like – and the ankle adapts," says lead scientist Prof. Michael Goldfarb. "You can walk up slopes, down slopes, up stairs and down stairs, and the device figures out what you're doing and functions the way it should."

It is hoped that the technology will be commercialized within the next two years. The ankle is demonstrated in the video below.

Engineers at Michigan Technological University have also developed an auto-adjusting prosthetic ankle, that uses a camera to scan the ground ahead.