Real time monitoring of transtibial elevated vacuum prostheses: a case series on socket air pressure

Abstract

Elevated vacuum is a prosthetic suspension method used to reduce slippage between the prosthetic socket and the residual limb. Evaluation of the effectiveness of these systems is limited due to a lack of correlation to actual socket air pressure, particularly during unconstrained movements. This may explain some of the variability in functional outcomes reported in the literature. We developed a light-weight portable socket measurement system to quantify internal socket air pressure, temperature, and acceleration. We implemented the system onto the sockets of three transtibial prosthesis users with mechanical elevated vacuum pumps. Participants completed five functional tasks with and without the vacuum pumps actively connected, including the 2-Minute Walk test, 5-Times Sit-to-Stand test, 4-Square Step test, L-Test, and Figure-8 test. Results demonstrated that the use of elevated vacuum pumps produced different gait profiles and pressure ranges for each user, with significant differences between pump conditions. Two of the participants demonstrated substantially lower air pressure (higher vacuum) over time while the pump was active compared to inactive. The minimum air pressure measured at the completion of the 2-Minute Walk test was -34.6 {+/-} 7.7 kPa, which is not as low as pressures reported in literature during benchtop experiments. One participant did not show substantial changes in pressure over time for either pump condition. Functional task performance was not significantly different between pump conditions. Correlation with accelerometer readings allowed air pressure data to be aligned with the gait cycle; peak positive pressures occurred just following initial contact of the foot in early stance, and the most negative pressures (vacuum) were observed throughout swing. This study has demonstrated the use of a portable data logging tool that may serve the clinical and research communities to quantify the operation of elevated vacuum systems, and better understand the variability of mechanical pump operation and overall system performance.