Timothy R. Myers

Effects of elevated vacuum on in-socket residual limb fluid volume

Bioimpedance analysis was used to measure the residual limb fluid volume of seven transtibial ampu- tee subjects using elevated vacuum sockets and nonele- vated vacuum sockets. Fluid volume changes were assessed during sessions with the subjects sitting, stand- ing, and walking. In general, fluid volume losses during 3 or 5 min walks and losses over the course of the 30 min test session were less for elevated vacuum than for suc- tion. Numerous variables, including the time of day that data were collected, soft tissue consistency, socket-to- limb size and shape differences, and subject health, may have affected the results and had an equivalent or greater effect on limb fluid volume compared with elevated vac- uum. Researchers should well consider these variables in the study design of future investigations on the effects of elevated vacuum on residual limb volume.

Clinical Utility of In-Socket Residual Limb Volume Change Measurement: Case Study Results

Bioimpedance analysis was used to measure conductive tissue extracellular fluid (ECF) volume changes in the residual limbs of four unilateral transtibial amputee subjects during standing and walking conditions. Results showed that all residual limbs experienced ECF volume decreases during 5 min standing intervals. During 5 min of walking immediately after a standing interval, the residual limbs of healthy subjects increased in ECF volume while those of diseased subjects, one with peripheral vascular disease and another with cardiovascular insufficiency and a high-salt intake, decreased. One subject demonstrated less absolute value ECF volume change during standing and walking at 12 months post-surgical revision compared with at six months. Presentation of bioimpedance data to patients improved compliance to practitioner recommendations and patient understanding. Results were useful towards clinical assessment, patient education, and decision-making about treatment.

Preliminary investigation of residual-limb fluid volume changes within one day

The purpose of this research was to investigate rates of residual-limb fluid volume change within one day for people with transtibial limb loss. Rates of fluid volume change during 30 min test sessions of sitting, standing, and walking activities were measured twice a day, once in the morning and once in the afternoon, on 12 regular prosthesis users with the use of bioimpedance analysis. Between test sessions, all subjects consumed food and drink, and subject activity ranged from low to high. The rate of fluid volume change within sessions ranged from -8.5 to 5.9 %/h (median: -2.2%/h). The rate of fluid volume change between sessions ranged from -2.7 to 0.9 %/h (median: -1.0%/h). The between-session rate of fluid volume change correlated highly with afternoon within-session rates of change (r = 0.9) but was not well correlated with morning within-session rates of change (r = 0.8). Subjects with peripheral arterial complications showed greater fluid volume loss rates during test sessions than between sessions. Rate of fluid volume change may be affected by sitting, standing, and walking activities; presence of peripheral arterial complications; being female; time since amputation; and wearing the socket without doffing for extended periods.

Central fabrication: carved positive assessment

Background: It is estimated that only 24% of practitioners use CAD/CAM regularly. Socket manufacturing error may be a source of the limited use of central fabrication. Objectives: The purpose of this study was to investigate the differences in shape between computer-manufactured, centrally fabricated carved models and electronic file shapes, to determine if carving was a major source of socket manufacturing error in central fabrication. Study design: Experimental, mechanical assessment. Methods: Three different trans-tibial model shapes were sent electronically to each of 10 central fabrication facilities for the fabrication of positive foam models. A custom mechanical digitizer and alignment algorithm were used to measure the model shapes and then compare them with the electronic file shapes. Results: Volume differences between the models and the electronic file shapes ranged from −4.2% to 1.0%, and averaged −0.9 (SD = 1.1)%. Mean radial error ranged from −1.2 mm to 0.3 mm and averaged −0.3 (SD = 0.3) mm. Inter-quartile range was between 0.3 mm and 2.7 mm and averaged 0.6 (SD = 0.5) mm. The models were significantly smaller than sockets made from the same electronic file shapes (p < 0.01), but the range of mean radial error and the interquartile range were not significantly different between the models and sockets. Conclusions: The results demonstrated that there was considerable variability in model quality among central fabricators in the industry, and that carving was not the sole source of socket fabrication error. Clinical relevance The results provide insight into the severity and nature of carving error by central fabrication facilities. Because we found a wide range of model quality, there is not a consistent fabrication problem across the industry, but instead some central fabrication facilities practice the art of model fabrication better than others.

Post-doffing residual limb fluid volume change in people with trans-tibial amputation.

Background: Residual limb volume may change after doffing, affecting the limb shape measured and used as a starting point for socket design. Objectives: The purpose of this study was to compare residual limb fluid volume changes after doffing for different test configurations. Study Design: The study was a repeated measures experimental design with three conditions (Sit, Liner, and Walk). Methods: Residual limb fluid volume on 30 people with trans-tibial amputation was measured using bioimpedance analysis. Three tests were conducted – Sit: sit for 10 minutes, remove the prosthesis, socks and liner, sit for 10 minutes; Liner: sit for 10 minutes, remove the prosthesis and socks but not the liner, sit for 10 minutes; Walk: conduct sit, stand and walk activities for 30 minutes, remove the prosthesis, socks and liner, sit for 10 minutes. Results: The percentage fluid volume increase after doffing was significantly higher for Walk (2.8%) than for Sit (1.8%) (p = 0.03). The time to achieve a maximum or stable fluid volume was shorter for Liner (4.3 min) than for Sit (6.6 min) (p = 0.03). Conclusions: Activity before doffing intensified the post-doffing limb fluid volume increase. Maintaining a liner after doffing caused limb fluid volume to stabilize faster than removing the liner. Clinical relevance To minimize residual limb volume increase before casting or imaging, practitioners should have patients sit with their prosthesis donned for 10 minutes. Leaving a liner on the residuum will not reduce the post-doffing volume increase, but it will help to more quickly achieve a consistent limb fluid volume.

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

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.