New software that can be incorporated into powered lower-lower limb prosthetic devices to automatically tune the amount of power a prosthetic limb needs for a patient to walk comfortably has been developed by researchers at North Carolina State University (NC State) and the University of North Carolina at Chapel Hill (UNC-Chapel Hill). The software can make it easier for prosthesis users to walk, reduce the number of visits to prosthetists, and allow a prosthesis to adjust to changing conditions, all of which will make the devices more functional and lower the costs associated with powered prosthetic use. The software, however, needs improvement to better match the prosthetists’ skills, according to the researchers. The study was published online September 25 in the Annals of Biomedical Engineering.
The researchers studied stiffness and damping control in powered lower-limb prostheses, noting that making such adjustments are time and resource intensive, to develop a novel cyber expert system (CES) that encoded prosthetists’ tuning decisions as computer rules to automatically tune control parameters for a powered knee (passive ankle) prosthesis. The system works by taking into account the angle of the prosthetic knee while walking; it adjusts the amount of power the prosthesis receives in real time to maintain the proper angle.
CES tuning performance was preliminarily quantified with two able-bodied subjects and two subjects with transfemoral amputations. After CES and prosthetist tuning, the researchers observed normative prosthetic knee kinematics and improved or slightly improved gait symmetry and step width within each subject. Compared to the prosthetist’s tuning, the CES tuning procedure required less time and no human intervention. The authors noted that although CES for automatically tuning prosthesis control is a sound concept that promises to enhance the practical value of powered prosthetic legs, the tuning goals of CES might not fully capture those of the prosthetist because tuning by a prosthetist reduced trunk sway, while CES sometimes led to slightly increased trunk motion. Additional research is needed to identify more appropriate tuning objectives for powered prosthetic legs, according to the study.
“In testing, we found that the computer-using the algorithm-performed better than prosthetists at achieving the proper joint angle,” said He (Helen) Huang, PhD, lead author of the study, and associate professor of biomedical engineering at NC State and UNC-Chapel Hill. “So we know our approach works. But we’re still working to make it better. Prosthetists rely on years of experience to not only adjust the joint angle, but to adjust a prosthesis to help patients maintain a comfortable posture while walking,” Huang adds. “We’re not yet able to replicate the prosthetist’s success in achieving those comfortable ‘trunk motions,’ but it’s something we’re working on.”
Editor’s note: This story was adapted from materials provided by NC State.
To watch a video before and after the tuning software is employed, click here.