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Refining Prosthetic Legs - One Accident at a Time

Shown here, 71-year-old Marjorie Brasier, one of six volunteers with prosthetic legs, walked semi-confidently on a treadmill, with instruments monitoring her prosthetic, and her thigh nerve bundles. Again and again she tripped or slipped. Sometimes she recovered on her own and kept walking, while at other times the harness she wore was all that kept her from tumbling to the floor.

When it comes to advanced prosthetic limbs - or for that matter virtual limbs relying on the same basic principles, getting the control circuitry to function properly is crucial. One of the most important aspects of said control circuitry, is the neural coding that binds the limb to the nerve impulses of the surviving ends of the peripheral nervous system.

A great deal of data is regularly passed both ways between an organic human body and a natural arm or leg. We have managed to tap into and translate some of it, in order to have a prosthetic leg respond semi-naturally to unconscious commands such as walking or climbing stairs, but we have by no means gotten even close to reverse engineering every signal along every nerve fibre.

One of the many areas of succh natural data that remains largely untapped, but which is vital to normal walking, is the signal set that passes to the leg automatically when we trip or stumble and the brain tries to regain balance. In prosthetics, this reflex is missing, causing the person to compensate with their other limbs, consciously, or fall over.

It has therefore fallen to a group of researchers at the University of Rhode Island in the US, to try and correct this issue. If not fully, at least to the point where our understanding of such reflex actions allows the signals to be detected and answered by the prosthetic, or virtual limb.

"When we become unbalanced, our neural system reacts quickly and sends a signal to help us recover," said He (Helen) Huang, assistant professor of biomedical engineering at URI. "Our challenge is to see if we can detect these neural reactions fast enough to activate a mechanism in a patient's prosthetic leg to stabilise them before they fall."

Six volunteers, each of which possessed a prosthetic leg with some degree of binding to their peripheral nervous system, were selected to take place in the trials. The video below, shows 71-year-old Marjorie Brasier, one of these six, going through her paces on the treadmill. Brasier was hooked up to dozens of electrodes, wore shoes containing 99 pressure sensors, and 40 light-reflective markers on her body were tracked by eight cameras surrounding the room to collect the data necessary for the research.

Unfortunately, people such as her are not the ideal type of candidate for studies such as this one. The reason for this is that Majorie has had a prosthetic leg for some years, and her body has become used to compensating for it. Thus, her responses to a trip or stumble, are not the same at a base level, as someone who is freshly used to a natural leg and fully functioning capabilities of such.

It would perhaps have been more ideal to study the signals of those with their original legs, for this reason.

Thankfully, the researchers have realised this, and a second, parallel study by the same team, is ongoing, to collect ad compare just this sort of data. What the team are looking for at this time, is something similar to event related potential, or ERP activity in the limb's nerves - a regular, definable signal of activity that is duplicable across individuals when the same manner of trip occurs. Once this is found, by studying the variance in signal over different types and intensities of trip and stumble, a rough guide to the neural coding can be ascertained. This can then hopefully be used to program the leg with how to respond with a reflex action.

"If we can detect the stumble reaction fast enough, then there may be time to react to it," said Huang, who is collaborating on the project with Brown University Assistant Professor Susan D'Andrea. "Hopefully we can develop a system that can mimic the normal human reaction to stumbling."

According to the URI researcher, the population of lower-limb amputees in the United States is large and growing, especially so during this time of war, and she believes that the design of a high performing prosthetic leg is critical to reducing the burden of this disability.

"We need to give a lot of credit to the patients involved in this study as they are allowing us the opportunity to collect unprecedented data related to stumble and recovery reactions in amputees," said Michael Nunnery, owner of Nunnery Orthotic and Prosthetic Technologies, Inc., another partner in the research project. "We hope to utilize this data to have an innovative impact on the future of above knee amputee prosthetics needs. "


URI researcher trips amputees in effort to develop improved prosthetic legs


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