Most of the existing research on robotic prosthetic ankles has focused solely on walking using autonomous control. Autonomous control, in this context, means that while the person wearing the prosthesis decides whether to walk or stand still, the fine movements involved in those movements happen automatically - rather than because of anything the wearer is doing.
Huang, Fleming and their collaborators wanted to know what would happen if an amputee, working with a physical therapist, trained with a neurally 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 in this study reads electrical signals from two residual calf muscles. Those calf muscles 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.
After training, the study participant was able to do a variety of tasks that had been difficult before, such as going from sitting to standing without any external assistance or squatting to pick something up off the ground without compensating for the movement with other body parts. But one of the most pronounced differences was the study 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 level of confidence in his own stability.
"The concept of mimicking natural control of the ankle is very straightforward," Huang says. "But implementation of this concept is more complicated. It requires training people to use residual muscles to drive new prosthetic technologies. The results in this case study were dramatic. This is just one study, but it shows us what is feasible."
"There is also a profound emotional impact when people use powered prosthetic devices that are controlled by reading the electrical signals that their bodies are making," Fleming says. "It is much more similar to the way people move intuitively, and that can make a big difference in how people respond to using a prosthesis at all."
The researchers are already having more people go through the training paradigm and are expanding their testing to assess the results of that training.
"Powered prostheses that exist now are very expensive and are not covered by insurance," Fleming says. "So there are issues related to access to these technologies. By attempting to restore normal control of these type of activities, this technology stands to really improve quality of life and community participation for individuals with amputation. This would make these expensive devices more likely to be covered by insurance in the future if it means improving the overall health of the individual."
COMPAMED-tradefair.com; Source: North Carolina State University
