May 2021

POWERED PROSTHETIC ANKLES CAN RESTORE A WIDE RANGE OF FUNCTIONS FOR AMPUTEES

When the participant used his daily prosthesis (left) he had a limited range of motion and had to bend his back significantly to lift objects off the ground. When using a neural controlled prosthetic ankle (right) he was able to voluntarily control his prosthetic ankle joint force and angle and keep a healthy posture while lifting weight from the ground. Image courtesy of Aaron Fleming.

Researchers from North Carolina State University (NC State) and the University of North Carolina (UNC) at Chapel Hill have demonstrated that, with training, neural control of a powered prosthetic ankle can restore a wide range of abilities, including standing on challenging surfaces and squatting.

Helen Huang PhD, the Jackson Family Distinguished Professor in the Joint Department of Biomedical Engineering (BME) at NC State and UNC; Aaron Fleming, a PhD candidate in the joint BME department; and their collaborators wanted to know what would happen if an amputee, working with a physical therapist (PT), trained with a neural controlled powered prosthetic ankle on activities that are challenging with typical prostheses. Would it be possible for amputees to regain a fuller range of control in the many daily motions that people make with their ankles in addition to walking?

The powered prosthesis they used reads electrical signals from 2 residual calf muscles, which are responsible for controlling ankle motion. The prosthetic technology uses a control paradigm developed by the researchers to convert electrical signals from those muscles into commands that control the movement of the prosthesis.

The participant, who has a left transtibial amputation, was fitted with the prosthesis and underwent an initial evaluation. He then had 5 2-hour-long training sessions with a PT over 2 ½ weeks, followed by a second evaluation. After training, the participant could do a variety of tasks that had been difficult before, such as going from sitting to standing without assistance or squatting to pick something up off the ground without compensating for the movement with other body parts. One of the most pronounced differences was the participant’s stability, whether standing or moving. This was reflected in both empirical evaluations, such as testing the patient’s stability when standing on foam, and in the patient’s confidence level in his own stability.

The researchers are already having more people go through the training paradigm and are expanding their testing to assess the results of that training and how broadly applicable the findings may be. The researchers also want to conduct real-world beta testing.

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