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

Abstract

Prosthetic elevated vacuum is a suspension method used to reduce daily volume changes of 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. Our objective was to develop a light-weight portable socket measurement system to quantify internal socket air pressure, temperature, and acceleration; and to present preliminary results from implementation with 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 different gait profiles and pressure ranges for each user. 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 for all participants was -34.6 ± 7.7 kPa. 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 indicated peak positive pressures occurred just following initial contact of the foot in early stance, and the most negative pressures (highest 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.

Lower limb prosthetic interfaces

“…31,[58][59][60] Variability in performance of a mechanical vacuum pump in a transtibial socket was tested by logging socket air pressure over time during functional tasks. 61 The socket showed a decrease in socket air pressure of −34.6 ± 7.7 kPa over 10 gait cycles during a 2-min walk test, but no significant difference in task performance was observed between vacuum and suction conditions, perhaps due to the short test duration. 61 A study by Xu et al 62 revealed that higher vacuum levels in transtibial VASS sockets (50-67 kPa) appeared to be more comfortable and improved loading of the intact limb, but also increased hip and knee external adduction moments, potentially increasing the risk of knee osteoarthritis on the amputated side; while lower vacuum levels adversely affected gait symmetry.…”

A Cost-Effective Inertial Measurement System for Tracking Movement and Triggering Kinesthetic Feedback in Lower-Limb Prosthesis Users

“…Although such microprocessor-controlled lower-limb prostheses rely on IMUs to monitor the prostheses’ movement and facilitate their optimal performance (e.g., by adapting to varying terrains [ 4 ]), the majority of lower-limb prostheses do not [ 19 , 20 ]. Additionally, acquiring movement data wirelessly from advanced prostheses is difficult without compromising their integrity and making physical modifications to the system [ 21 ]. Thus, retrofitting prosthetic devices with easy-to-attach, low-cost, wireless IMUs may aid researchers in acquiring prosthesis movement data, for use in closed-loop feedback systems utilizing the KI.…”