How does adding and removing liquid from socket bladders affect residual-limb fluid volume?

Abstract

Adding and removing liquid from socket bladders is a means for people with limb loss to accommodate residual-limb volume change. We fit 19 people with transtibial amputation using their regular prosthetic socket with fluid bladders on the inside socket surface to undergo cycles of bladder liquid addition and removal. In each cycle, subjects sat, stood, and walked for 90 s with bladder liquid added, and then sat, stood, and walked for 90 s again with the bladder liquid removed. The amount of bladder liquid added was increased in each cycle. We used bioimpedance analysis to measure residual-limb fluid volume. Results showed that the preferred bladder liquid volume was 16.8 +/- 8.4 mL (mean +/- standard deviation), corresponding with 1.7% +/- 0.8% of the average socket volume between the bioimpedance voltage-sensing electrodes. Residual-limb fluid volume driven out of the residual limb when bladder liquid was added was typically not recovered upon subsequent bladder liquid removal. Of the 19 subjects, 15 experienced a gradual residual-limb fluid volume loss over the test session. Care should be taken when implementing adjustable socket technologies in people with limb loss. Reducing socket volume may accentuate residual-limb fluid volume loss.

Figures

FIGURE 1. A-C. Hypothesized response

Plots indicate the expected interactions between bladder liquid volume changes and residual limb fluid volume.

FIGURE 2. Instrumented socket

View inside socket with bladders in place.

FIGURE 3. Residual limb instrumented with bioimpedance electrodes

FIGURE 4. A-C. Example results from a subject

Results are typical. A: Percentage residual limb fluid volume change for each bladder liquid addition and removal. The subject showed a gradual decrease in fluid volume over the session, with increased loss when bladder liquid was added. B: Percentage limb fluid volume change vs. percentage of socket volume change for each bladder liquid addition. C: Fluid transport compliance for each bladder liquid addition.

FIGURE 4. A-C. Example results from a subject

Results are typical. A: Percentage residual limb fluid volume change for each bladder liquid addition and removal. The subject showed a gradual decrease in fluid volume over the session, with increased loss when bladder liquid was added. B: Percentage limb fluid volume change vs. percentage of socket volume change for each bladder liquid addition. C: Fluid transport compliance for each bladder liquid addition.

FIGURE 4. A-C. Example results from a subject

Results are typical. A: Percentage residual limb fluid volume change for each bladder liquid addition and removal. The subject showed a gradual decrease in fluid volume over the session, with increased loss when bladder liquid was added. B: Percentage limb fluid volume change vs. percentage of socket volume change for each bladder liquid addition. C: Fluid transport compliance for each bladder liquid addition.

FIGURE 5. A-S. Limb fluid transport compliance

Results for all nineteen subjects are shown. A-I: Subjects were at the primary inflection point or a minimum in their transport compliance curve when the most comfortable bladder liquid setting was reached, indicated in the lot by a transition to a red line. J-M: Subjects were beyond the primary inflection point when the most comfortable bladder liquid setting was reached. N-O: Subjects for whom the bladder broke during testing. P-S: Subjects showed an initial increase in limb fluid transport compliance, followed by a decrease.