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Introduction: Typical practitioners choose from among only two to three products when selecting liners for their patients. A lack of comparable objective information about similarities and differences among elastomeric liner products may be part of the reason. Methods: Commonly used, commercially available polyurethane, silicone, and thermoplastic elastomer (TPE) liners were tested for their compressive, shear, tensile, and volumetric elasticities as well as their coefficients of friction (CoFs) and thermal conductivities. Results: Polyurethane and silicone liners tended to be stiffer in compression and shear than TPE liners. Fabric backings contributed primarily to increased tensile elasticity (and thus reduced pistoning). Polyurethane liners demonstrated relatively low CoFs, whereas silicone and TPE liners had higher CoFs and wider ranges. All materials tested were essentially incompressible. Thermal conductivities of all materials were comparable and similar to that of leather. Conclusions: Polyurethane liners are softer and less sticky than 16 years ago, and TPE liners have higher tensile stiffness than previously. A stiff fabric backing can increase tensile stiffness by more than 200%. Compressive stiffness may be used to characterize a liner's ability to flow. Elastomeric liners move heat almost exclusively via conduction. [ABSTRACT FROM AUTHOR]

Introduction: The purpose of this research was to develop a retractable tethered pin system to facilitate partial doffing and redonning of prosthetic sockets with locking-pin suspension. Materials and Methods: The system included a tethered cord th at extended from a retracting mechanism on the pylon th rough the shuttle lock to a clip at the bottom of the locking pin. The mechanism operated similarly to a seatbelt retractor, applying low-level tension unless the user made a rapid pull on the tether to lock the mechanism. Results: Evaluation tests on four people with limb loss demonstrated th at users liked the retracting m echanism and its capability to facilitate partial doffing and redonning. However, participants reported that the clip used to connect the mechanism to the locking pin worsened initial donning and final doffing of the socket. Conclusions: Modifications to the retractable tethered pin system design may overcome limitations and result in an easy and effective accommodation technology for people with transtibial amputation. [ABSTRACT FROM AUTHOR]

Objective: The objective of this research was to develop a bioimpedance platform for monitoring fluid volume in residual limbs of people with trans-tibial limb loss using prostheses. Methods: A customized multifrequency current stimulus profile was sent to thin flat electrodes positioned on the thigh and distal residual limb. The applied current signal and sensed voltage signals from four pairs of electrodes located on the anterior and posterior surfaces were demodulated into resistive and reactive components. An established electrical model (Cole) and segmental limb geometry model were used to convert results to extracellular and intracellular fluid volumes. Bench tests and testing on amputee participants were conducted to optimize the stimulus profile and electrode design and layout. Results: The proximal current injection electrode needed to be at least 25 cm from the proximal voltage sensing electrode. A thin layer of hydrogel needed to be present during testing to ensure good electrical coupling. Using a burst duration of 2.0 ms, intermission interval of 100 μs, and sampling delay of 10 μs at each of 24 frequencies except 5 kHz, which required a 200-μs sampling delay, the system achieved a sampling rate of 19.7 Hz. Conclusion: The designed bioimpedance platform allowed system settings and electrode layouts and positions to be optimized for amputee limb fluid volume measurement. Significance: The system will be useful toward identifying and ranking prosthetic design features and participant characteristics that impact residual limb fluid volume. [ABSTRACT FROM PUBLISHER]

For people who wear a prosthetic limb, residual-limb fluid volume loss during the day may be problematic and detrimentally affect socket fit. The purpose of this research was to test the capability of a novel liner with adjustable bladders positioned within its wall to mitigate volume loss and facilitate limb fluid volume recovery and retention. Bioimpedance analysis was used to monitor fluid volume changes in the anterior and posterior residual limb of participants with transtibial amputation. Participants underwent six cycles of sitting for 90 s, standing for 90 s, and walking for 5 min with liquid within the bladder-liners. Between the third and fourth cycles, participants sat for 10 min with liquid left within the bladders (Liquid-In) or removed (Liquid-Out). Results showed that participants recovered more fluid volume during the 10 min of sitting with Liquid-Out than Liquid-In (p = 0.09 for anterior and p = 0.04 for posterior). However, those fluid volume recoveries were not well retained in the short term (after the fourth cycle) or the long term (after the sixth cycle). Physiologic differences between sessions, reflected in the rates of fluid volume change at the outset of the session, and excessive stiffness of the bladder-liners may have affected fluid volume retentions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A device using radio frequency identification (RFID) technology was developed to continuously monitor sock use in people who use prosthetic limbs. RFID tags were placed on prosthetic socks worn by subjects with transtibial limb loss, and a high-frequency RFID reader and antenna were placed in a portable unit mounted to the outside of the prosthetic socket. Bench testing showed the device to have a maximum read range between 5.6 cm and 12.7 cm, depending on the RFID tag used. Testing in a laboratory setting on three participants with transtibial amputation showed that the device correctly monitored sock presence during sitting, standing, and walking activity when one or two socks were worn but was less reliable when more socks were used. Accurate detection was sensitive to orientation of the tag relative to the reader, presence of carbon fiber in the prosthetic socket, pistoning of the limb in the socket, and overlap among the tags. Use of ultra-high-frequency RFID may overcome these limitations. With improvements, the technology may prove useful to practitioners prescribing volume accommodation strategies for patients by providing information about sock use between clinical visits, including timing and consistency of daily sock-ply changes. [ABSTRACT FROM AUTHOR]

The objective of this research was to use computer-aided design software and a tabletop 3-D additive manufacturing system to design and fabricate custom plastic inserts for trans-tibial prosthesis users. Shape quality of inserts was tested right after they were inserted into participant's test sockets and again after four weeks of wear. Inserts remained properly positioned and intact throughout testing. Right after insertion the inserts caused the socket to be slightly under-sized, by a mean of 0.11 mm, approximately 55% of the thickness of a nylon sheath. After four weeks of wear the under-sizing was less, averaging 0.03 mm, approximately 15% of the thickness of a nylon sheath. Thus the inserts settled into the sockets over time. If existing prosthetic design software packages were enhanced to conduct insert design and to automatically generate fabrication files for manufacturing, then computer manufactured inserts may offer advantages over traditional methods in terms of speed of fabrication, ease of design, modification, and record keeping. [ABSTRACT FROM AUTHOR]

The purpose of this research was to conduct a preliminary effort to identify quantitative metrics to distinguish a good socket from an oversized socket in people with trans-tibial amputation. Results could be used to inform clinical practices related to socket replacement. A cross-over study was conducted on community ambulators (K-level 3 or 4) with good residual limb sensation. Participants were each provided with two sockets, a duplicate of their as-prescribed socket and a modified socket that was enlarged or reduced by 1.8 mm (∼6% of the socket volume) based on the fit quality of the as-prescribed socket. The two sockets were termed a larger socket and a smaller socket. Activity was monitored while participants wore each socket for 4 weeks. Participants’ gait; self-reported satisfaction, quality of fit, and performance; socket comfort; and morning-to-afternoon limb fluid volume changes were assessed. Visual analysis of plots and estimated effect sizes (measured as mean difference divided by standard deviation) showed largest effects for step time asymmetry, step width asymmetry, anterior and anterior-distal morning-to-afternoon fluid volume change, socket comfort score, and self-reported utility. These variables may be viable metrics for early detection of deterioration in socket fit, and should be tested in a larger clinical study. [ABSTRACT FROM AUTHOR]