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.

Fig 1. Installation of data logger onto prosthetic socket.

Modified sockets for (a) Participant 1, (b) Participant 2, and (c) Participant 3.

Fig 2. Overall gauge pressure data during 2-Minute Walk test.

Data is shown across (a) Participant 1, (b) Participant 2, and (c) Participant 3. Thin lines indicate raw data and thick lines indicate measurements smoothed using the rloess function in Matlab.

Fig 3. Individual gauge pressure stride data during 2-Minute Walk test.

Data is shown with pump inactive (top) and pump active (bottom), across (a) Participant 1, (b) Participant 2, and (c) Participant 3. Blue indicates the first stride and yellow the last, with the legend indicating total stride count.

Fig 4. Normalized individual stride data during 2-Minute Walk test.

Data is shown for gauge pressure (top) and magnitude of acceleration (bottom), across (a) Participant 1, (b) Participant 2, and (c) Participant 3. Dark lines indicate average measurements, with shaded areas indicating standard deviation.

Fig 5. Comparison of qualitative survey scores.

Solid colour bars indicate inactive pump condition scores and hatched bars indicate active pump condition scores, with error bars indicating standard deviation.