About half of the one million people in the United States with lower-limb amputation experience a fall each year, usually during walking. These falls often result in serious injury, with annual health care costs of over one billion dollars. Side-to-side motions are least stable during walking, especially on uneven terrain, and require more active control for balance. Surprisingly, little is known about how balance is affected by prosthesis properties that influence side-to-side motions. While robotic prostheses have improved propulsion and energy cost, this technology has not yet been used to improve stability or reduce fall risk. This project explores new approaches to the control of side-to-side balance using robotic prostheses, characterizes the effects of prosthesis parameters on stability, and establishes quantitative cost-benefit relationships for balance-related performance. It will yield new fundamental understanding of the role of ankle control in human balance and of the impact of instability on other aspects of gait and mobility. The project will develop technologies that lead to reduced fall rates, increased satisfaction and enhanced mobility for individuals with amputation, improving quality of life. Active, semi-active and passive prosthesis elements that enhance balance are being developed and their relative costs and benefits quantified along key dimensions, facilitating rational design choices. This will lead to increased efficiency in health care delivery, with increases in device cost being offset by reductions in costs for treating fall-related injuries. This project takes place in an interdisciplinary educational setting, in which doctoral, Master's and undergraduate students interact with clinical experts and gain experience in developing technologies to address disability. This compelling application of technology to improve people's well-being attracts new participants to science and engineering, enhancing the recruitment of female and minority students. A private-sector partner is helping to address commercial translation.
This project establishes new techniques for stabilizing amputee gait and compares implementation costs to balance-related benefits in terms of stability, metabolic energy use, and balance confidence. Experiments utilize a previously-developed, tethered ankle-foot prosthesis with high-fidelity torque control in both plantarflexion and inversion-eversion directions. This tool enables a new class of rapid, well-controlled tests of the effects of prosthesis features and control on human performance. The project team includes experienced physicians, prosthetists, entrepreneurs and researchers to ensure medical, clinical, commercial and scientific relevance. The primary goals of the project are: Goal 1: Develop new prosthesis control methods to stabilize amputee gait. Several promising techniques are being examined in experiments with unilateral trans-tibial amputees, including: i) once-per-step ankle push-off work modulation based on medial-lateral center of mass velocity, a technique the investigators previously established in simulations and experiments with non-disabled subjects; ii) once-per-step inversion-eversion torque modulation, expected to further enhance side-to-side balance; iii) once-per-step surface matching, expected to mitigate the effects of ground irregularities; and iv) optimized inversion-eversion stiffness, expected to modestly improve balance at low implementation cost. These methods are independently examined in separate tests and then compared. Participants are subjected to irregular terrain, a common balancing challenge for amputees. Performance is measured in terms of gait variability, metabolic rate, muscle activity, and self-reported confidence and preference. Goal 2: Cost-benefit analysis of stabilization techniques. Active control techniques, such as push-off work modulation, require expensive, high-power motors and large batteries. Semi-active techniques, such as surface matching, could be implemented with smaller, less-expensive actuation schemes. Estimates of implementation costs are combined with experimentally measured benefits to determine relationships between cost and benefit for each outcome and identify Pareto-optimal prosthesis characteristics.