Fitting Socket Research Articles

A Survey of Prosthetists' Perspectives on Adjustable-Volume Lower-Limb Prosthetic Sockets

ABSTRACT Introduction Adjustable-volume prosthetic sockets have been available for many years to address residual limb volume changes, although little research has been conducted regarding their efficacy. As such, prosthetists are guided by patient preference, personal experience, and professional perception. The purpose of this study was to explore clinician perceptions and experiences fitting adjustable-volume prosthetic sockets. Materials and Methods An anonymous online survey was distributed to certified prosthetists. The survey contained questions about prosthetists' demographics, whether they had previously fit an adjustable-volume prosthetic socket, whether these fittings were successful, and what challenges they experienced. Those who had not previously fit adjustable sockets were asked what barriers had prevented them from doing so. Results A total of 221 certified prosthetists completed the survey. Of the 195 eligible respondents, 82% had experience in fitting adjustable prosthetic sockets. The most commonly fit socket styles were the RevoFit (n = 123), Socket-less (n = 67), and Infinite (n = 66) sockets. Prosthetists had varied success with the different socket styles, with the RevoFit being the most successful, and the Infinite and Socket-less sockets the least successful. Respondents most frequently noted increased bulk (93% of respondents; n = 181), complicated fabrication (72%; n = 141), and poor cosmesis (65%; n = 127) as challenges faced when fitting adjustable-volume sockets. Some respondents felt these sockets were a useful clinical tool; however, common themes regarding clinical perception of adjustable sockets included issues with cost/reimbursement and appropriateness for only a subset of the population of individuals with amputation only. Other respondents felt that adjustable sockets were either not adequate for clinical use or required improvements before their use would be beneficial. Conclusions There is no majority opinion regarding the benefits and challenges of adjustable sockets among prosthetists. In general, prosthetists feel that adjustable sockets can be used as one of the various tools to accommodate complicated lower-limb fittings. Additional work is needed to provide clinicians with a best practice guideline for providing adjustability within lower-limb sockets. Clinical Relevance The study showed that prosthetists feel that adjustable sockets can be one of the tools used for complicated lower-limb fittings. Additional work is needed to develop a best practice guideline for providing adjustability in lower-limb sockets.

Developing a control framework for self-adjusting prosthetic sockets incorporating tissue injury risk estimation and generalized predictive control.

To perform activities of daily living (ADL), people with lower limb amputation depend on the prosthetic socket for stability and proprioceptive feedback. Poorly fitting sockets can cause discomfort, pain, limb tissue injuries, limited device usage, and potential rejection. Semi-passively controlled adjustable socket technologies exist, but these depend upon the user's perception to determine safe interfacial pressure levels. This paper presents a framework for automatic control of an adjustable transtibial prosthetic socket that enables active adaptation of residuum-socket interfacial loading through localized actuators, based on soft tissue injury risk estimation. Using finite element analysis, local interfacial pressure vs. compressive tissue strain relationships were estimated for three discrete anatomical actuator locations, for tissue injury risk assessment within a control structure. Generalized Predictive Control of multiple actuators was implemented to maintain interfacial pressure within estimated safe and functional limits. Controller simulation predicted satisfactory dynamic performance in several scenarios. Actuation rates of 0.06-1.51kPa/s with 0.67% maximum overshoot, and 0.75-1.58kPa/s were estimated for continuous walking, and for a demonstrative loading sequence of ADL, respectively. The developed platform could be useful for extending recent efforts in adjustable lower limb prosthetic socket design, particularly for individuals with residuum sensory impairment.

Parametric Design and Hybrid Fabrication of Above-Knee Prosthesis.

India has a large number of above-knee amputation patients who require a prosthetic leg that is affordable, conformal, functional, and durable. Available low-cost solutions, such as Jaipur foot, employ gypsum plaster in the process of fabricating a fitting socket. This has four shortcomings: (1) requirement of trained technicians, (2) high possibility of manual errors leading to rework, (3) long production time of several hours, and (4) difficulty in scaling up for widespread application. An improved approach is presented here, which combines computer-aided parametric design and numerically controlled machining with manual thermoforming to overcome the above issues. The socket is semi-automatically designed based on 60 parameters, derived from 23 measurements obtained on the natural stump of a patient. The three-dimensional (3D) computer-aided design model of the socket can be used for additive manufacturing (3D printing), which was found to be accurate, but time-consuming and expensive. Hence, a hybrid process was evolved with the following three steps: computer numeric control machining of the stump and shank replica in polyurethane (PU) foam, followed by coating with suitable epoxy, and finally high-density polyethylene pipe thermoforming over the PU foam replicas. Three prostheses were fabricated using both conventional and hybrid processes and provided to volunteer patients. The hybrid process resulted in 28% reduction in overall fabrication time and improved satisfaction of patients due to better fit and comfort. The proposed approach can be adapted for mass customization, required to meet the large gap in demand and supply, especially in resource-constrained settings.

Capturing prosthetic socket fitment: Preliminary results using an ultrasound-based device.

The acceptance of advanced prosthetic systems by users requires overcoming unique challenges of fitting prostheses to unique user anatomies to achieve systematic performance across a user base. Variations among individuals introduce complexities in fitting the sockets. Due to the difficulty of measuring socket interface characteristics, there is a lack of quantifiable diagnostic fitment information available. As a result, the process of fitting sockets is currently a laborintensive, manual approach, and can often result in sockets that are uncomfortable, unstable, or impede full range of motion. Additionally, results can be difficult to reproduce reliably. A diagnostic tool has been developed to quantify the relative movement between the socket and the residual bone during the fitting process. The approach leverages low cost and high precision ultrasound transceivers and intuitive visualization software to provide quantifiable socket fitment data. The goal is to enable a systematic socket-fitting strategy that yields reliable and reproducible results. Human subject testing and results are presented that show movement tracking relative to a cuff with an ultrasound transducer with an RMSD of 0.36 mm.

Biomechanical analysis of the effect of congruence, depth and radius on the stability ratio of a simplistic 'ball-and-socket' joint model.

ObjectivesThe bony shoulder stability ratio (BSSR) allows for quantification of the bony stabilisers in vivo. We aimed to biomechanically validate the BSSR, determine whether joint incongruence affects the stability ratio (SR) of a shoulder model, and determine the correct parameters (glenoid concavity versus humeral head radius) for calculation of the BSSR in vivo.MethodsFour polyethylene balls (radii: 19.1 mm to 38.1 mm) were used to mould four fitting sockets in four different depths (3.2 mm to 19.1mm). The SR was measured in biomechanical congruent and incongruent experimental series. The experimental SR of a congruent system was compared with the calculated SR based on the BSSR approach. Differences in SR between congruent and incongruent experimental conditions were quantified. Finally, the experimental SR was compared with either calculated SR based on the socket concavity or plastic ball radius.ResultsThe experimental SR is comparable with the calculated SR (mean difference 10%, sd 8%; relative values). The experimental incongruence study observed almost no differences (2%, sd 2%). The calculated SR on the basis of the socket concavity radius is superior in predicting the experimental SR (mean difference 10%, sd 9%) compared with the calculated SR based on the plastic ball radius (mean difference 42%, sd 55%).ConclusionThe present biomechanical investigation confirmed the validity of the BSSR. Incongruence has no significant effect on the SR of a shoulder model. In the event of an incongruent system, the calculation of the BSSR on the basis of the glenoid concavity radius is recommended.Cite this article: L. Ernstbrunner, J-D. Werthel, T. Hatta, A. R. Thoreson, H. Resch, K-N. An, P. Moroder. Biomechanical analysis of the effect of congruence, depth and radius on the stability ratio of a simplistic ‘ball-and-socket’ joint model. Bone Joint Res 2016;5:453–460. DOI: 10.1302/2046-3758.510.BJR-2016-0078.R1.

Torsional locomotion.

One edge of an elastic rod is inserted into a friction-less and fitting socket head, whereas the other edge is subjected to a torque, generating a uniform twisting moment. It is theoretically shown and experimentally proved that, although perfectly smooth, the constraint realizes an expulsive axial force on the elastic rod, which amount is independent of the shape of the socket head. The axial force explains why screwdrivers at high torque have the tendency to disengage from screw heads and demonstrates torsional locomotion along a perfectly smooth channel. This new type of locomotion finds direct evidence in the realization of a ‘torsional gun’, capable of transforming torque into propulsive force.

Vacuum-Assisted Socket Suspension Compared With Pin Suspension for Lower Extremity Amputees: Effect on Fit, Activity, and Limb Volume

Klute GK, Berge JS, Biggs W, Pongnumkul S, Popovic Z, Curless B. Vacuum-assisted socket suspension compared with pin suspension for lower extremity amputees: effect on fit, activity, and limb volume. Objective To investigate the effect of a vacuum-assisted socket suspension system as compared with pin suspension on lower extremity amputees. Design Randomized crossover with 3-week acclimation. Setting Household, community, and laboratory environments. Participants Unilateral, transtibial amputees (N=20 enrolled, N=5 completed). Interventions (1) Total surface–bearing socket with a vacuum-assisted suspension system (VASS), and (2) modified patellar tendon–bearing socket with a pin lock suspension system. Main Outcome Measures Activity level, residual limb volume before and after a 30-minute treadmill walk, residual limb pistoning, and Prosthesis Evaluation Questionnaire. Results Activity levels were significantly lower while wearing the vacuum-assisted socket suspension system than the pin suspension ( P=.0056; 38,000±9,000 steps per 2wk vs 73,000±18,000 steps per 2wk, respectively). Residual limb pistoning was significantly less while wearing the vacuum-assisted socket suspension system than the pin suspension ( P=.0021; 1±3mm vs 6±4mm, respectively). Treadmill walking had no effect on residual limb volume. In general, participants ranked their residual limb health higher, were less frustrated, and claimed it was easier to ambulate while wearing a pin suspension compared with the VASS. Conclusions The VASS resulted in a better fitting socket as measured by limb movement relative to the prosthetic socket (pistoning), although the clinical relevance of the small but statistically significant difference is difficult to discern. Treadmill walking had no effect, suggesting that a skilled prosthetist can control for daily limb volume fluctuations by using conventional, nonvacuum systems. Participants took approximately half as many steps while wearing the VASS which, when coupled with their subjective responses, suggests a preference for the pin suspension system.

Stump/socket pressure profiles of the pressure cast prosthetic socket

Objective. The aim was to evaluate stump/socket interface pressure in amputees wearing a socket developed by a pressure casting system. Design. Five unilateral transtibial amputees wore a pressure cast socket and walked at a self-selected speed. Background. The socket produces equally distributed pressure at the stump/socket interface, deviating from the conventional belief that pressure varies in proportion to the pain threshold of different tissues in the stump. Methods. The socket was fabricated while the subject placed his stump in a pressure chamber. Pressure was applied while he adopted a normal standing position. A specially built strain gauged type pressure transducer was used for measuring pressure distribution. Pressure and gait parameters were measured simultaneously while the subjects were standing and walking. Results and conclusion. The pressure cast technique was able to provide comfortable fitting sockets. A hydrostatic pressure profile was not evident during standing or gait. Results also showed that no standard pressure profile for the pressure cast socket was observed. This was expected as no rectifications were done on the pressure cast socket. Pressure profiles at 10%, 25% and 50% of gait cycle did not correlate with the pressure profiles previously proposed. Relevance The hydrostatic theory is an attractive concept in socket design as it produces a stump/socket pressure profile that is evenly distributed. Furthermore, it is a method that is easily implemented, independent of a prosthetist’s skill and experience and reduces manufacturing time. However, there is still controversy surrounding the efficacy of this hydrostatic theory.

Handmade fixed partial prosthesis remover

J Prosthet Dent 2002;88:232-3.

9A21 即時試歩行可能な義足採型システムの開発

Immediate fitting socket (IFS) system was developed to shorten the long term for making of an artificial leg, by applying powder technology. The IFS is constructed of an outer shell and a particle containing bag, whose rigidity can be controlled by the applied negative air pressure. The shape modeling performance was evaluated by measuring the circumferences of the models from a plaster imitation and three amputees stump. The modeling error was less than 0.5% in plaster imitation, and less than 6% in amputees stump. The polymer sockets cast from the models were successfully utilized by the amputee.

Measurement of Socket Discomfort???Part II: Signal Detection

The purpose of the study was to demonstrate how the psychophysical theory of signal detection (SDT) can be applied to the process of fitting sockets and used to model the ability of patients to make judgments concerning the expectation of discomfort problems when uncertainty exists. For experimental purposes, a signal was defined as the ability of a patient to detect aspects of socket geometry that could lead to discomfort or tissue breakdown after initial fitting. An experiment was designed that consisted of varying the check socket geometries for three transtibial amputees by inserting 1.6-mm and 2.6-mm thick wafers at the distal tibia and fibula head and asking the subjects to report the degree of certainty they had regarding the discomfort the socket might produce after a day of use. In addition, psychophysical category ratio scales were used to measure the magnitudes of the pressure, discomfort, and pain perceived by the subjects for each experimental condition. Two of the subjects were experienced prosthesis users, and the third was an inexperienced individual in the process of being fitted for a first temporary prosthesis. One experienced subject indicated with maximum certainty that any alteration which reduced relief at the distal tibia and fibula head by even 0.6 mm, the thinnest insert in the experiment (a pressure-sensing element), would produce intolerable discomfort. However, the other two subjects provided good experimental data representing a range of uncertainties, and receiver operating characteristic (ROC) curves were fitted to their responses. The curves for the inexperienced subject for the weakest signals presented (1.6-mm thickness) indicated performance no better than pure guessing, but performance improved for the thicker wafers (2.6-mm thickness). The ROC curves for the remaining experienced subject indicated much less uncertainty with the thinnest wafer and nearly perfect signal detection for the thicker wafer. Possible explanations for these results are presented. The paper also discusses how the probabilities associated with the four possible outcomes of the judgment task—hit, miss, correct rejection, and false alarm—are dependent on the relative costs and benefits of the outcomes.

Bacteria on stumps of amputees and the effect of antiseptics

Amputees get stump infections usually from the natural inhabitants of the healthy skin and probably due to the unnatural environment of tight fitting sockets. The aim of the present study was to investigate the natural stump bacteria and the effect of antiseptics as well as the amputees' evaluation of such treatment. Fifteen amputees using their prostheses all day were investigated. Bacterial samplings were taken by swab technique with respect to bacteria and fungi from the stumps in the morning before prosthetic application and in the evening after a whole day's prosthetic use without antiseptic cleaning; after antiseptic cleaning with a combination of Isopropanol 45%. N-propanol 30% and N-cetyl-pyridiniumchloride 0.2% for one day: after fourteen days continuous use. The patients were asked if they liked the antiseptic and if they would like to continue to use it. Two patients did not submit bacteriological samples after the cleaning period. Before cleaning S. epidermidis, S. aureus and alpha-hemolytic streptococci were commonly found. In two instances gram negative rods were found. After the cleaning period there was a reduction of bacteria in 11 out of 13 patients. All patients liked the antiseptic and the simplicity by which the stumps and the sockets could be kept clean. The authors feel that the use of antiseptics to increase stump and socket hygiene is justified.