A comparison of trans-tibial amputee suction and vacuum socket conditions

Quantifying Bone and Skin Movement in the Residual Limb-Socket Interface of Individuals With Transtibial Limb Loss Using Dynamic Stereo X-Ray: Protocol for a Lower Limb Loss Cadaver and Clinical Study

BACKGROUND

Relative motion between the residual limb and socket in individuals with transtibial limb loss can lead to substantial consequences that limit mobility. Although assessments of the relative motion between the residual limb and socket have been performed, there remains a substantial gap in understanding the complex mechanics of the residual limb-socket interface during dynamic activities that limits the ability to improve socket design. However, dynamic stereo x-ray (DSX) is an advanced imaging technology that can quantify 3D bone movement and skin deformation inside a socket during dynamic activities.

OBJECTIVE

This study aims to develop analytical tools using DSX to quantify the dynamic, in vivo kinematics between the residual limb and socket and the mechanism of residual tissue deformation.

METHODS

A lower limb cadaver study will first be performed to optimize the placement of an array of radiopaque beads and markers on the socket, liner, and skin to simultaneously assess dynamic tibial movement and residual tissue and liner deformation. Five cadaver limbs will be used in an iterative process to develop an optimal marker setup. Stance phase gait will be simulated during each session to induce bone movement and skin and liner deformation. The number, shape, size, and placement of each marker will be evaluated after each session to refine the marker set. Once an optimal marker setup is identified, 21 participants with transtibial limb loss will be fitted with a socket capable of being suspended via both elevated vacuum and traditional suction. Participants will undergo a 4-week acclimation period and then be tested in the DSX system to track tibial, skin, and liner motion under both suspension techniques during 3 activities: treadmill walking at a self-selected speed, at a walking speed 10% faster, and during a step-down movement. The performance of the 2 suspension techniques will be evaluated by quantifying the 3D bone movement of the residual tibia with respect to the socket and quantifying liner and skin deformation at the socket-residuum interface.

RESULTS

This study was funded in October 2021. Cadaver testing began in January 2023. Enrollment began in February 2024. Data collection is expected to conclude in December 2025. The initial dissemination of results is expected in November 2026.

CONCLUSIONS

The successful completion of this study will help develop analytical methods for the accurate assessment of residual limb-socket motion. The results will significantly advance the understanding of the complex biomechanical interactions between the residual limb and the socket, which can aid in evidence-based clinical practice and socket prescription guidelines. This critical foundational information can aid in the development of future socket technology that has the potential to reduce secondary comorbidities that result from complications of poor prosthesis load transmission.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/57329.

Socket-residuum coupling integrity affects perception of external stimuli: Effects of altering the transtibial interface using vacuum-assisted suspension

BACKGROUND

Relative movement between the socket and residual limb can impair function in prosthesis users. It is plausible that, in addition to its mechanical effect, the integrity of the socket-residuum interface influences the ability of an individual to sense tactile cues through the prosthesis. Vacuum-assisted suspension (VAS) has been shown to reduce relative movement at this interface, providing a means to test this premise. The purpose of this pilot study was to assess the effects of altering socket-residuum interface integrity through the VAS pressure level on the thresholds of perception of an externally applied vibration stimulus.

METHODS

Seven unilateral transtibial prosthesis users participated. Socket-residual limb integrity was altered using the VAS subatmospheric (vacuum) pressure level. Vibration perception tests were conducted at low, mid, and high vacuum levels, targeting 0, 8, and 19 in Hg respectively, and performed in partially loaded and fully loaded conditions. Vibration intensity was increased using a dial until participants delivered a verbal signal indicating it was perceptible, and the nominal intensity was recorded.

RESULTS

Intensity thresholds decreased (ie, sensitivity increased) from low to high vacuum settings when fully loaded ( P = 0.008). Differences when partially loaded were nonsignificant and variable across participants.

CONCLUSION

This study provides preliminary evidence that altering the integrity between the socket and residual limb by modifying the vacuum level affects sensation related to the external environment experienced through the prosthesis, although translation of these findings to real-world stimuli remains to be tested.

Soft robotics-inspired sensing system for detecting downward movement and pistoning in prosthetic sockets: A proof-of-concept study

BACKGROUND

Vertical displacement of the residual limb within transtibial prosthetic socket, often known as "pistoning" or downward movement, may lead to skin breakdowns and ulcers. Downward movement is particularly difficult to self-manage for diabetic individuals living with amputation because of diminished sensation in the residual limb from peripheral neuropathy. Therefore, a customizable sensor at the distal end that can alert the users when high-risk downward movement and pistoning occurs is urgently needed.

OBJECTIVES

Presented herein for the first time is a lightweight, inexpensive sensing system inspired by soft robotics that can detect the occurrence and severity of downward movement at the distal end.

METHODS

The sensing system consists of a multilayered torus-shaped balloon, allowing easy integration with pin-lock socket systems. The design allows sensing of vertical displacement without imparting high reaction forces back onto the distal end. A benchtop compression tester was used to characterize system performance. Systematic and parametric benchtop tests were conducted to examine the sensor's physical characteristics. Long-term (24-h) stability of the sensor was also recorded.

RESULTS

Compared with water, air was determined to be a better medium with a higher linear full-scale span (FSS) because of its compressible nature. Repeatable 0.5-mm vertical displacements yielded a linear (>0.99 R2) FSS of 4.5 mm and a sensitivity of 0.8 kPa/mm. The sensing system is highly precise, with as low as 1% FSS total error band and average hysteresis of 2.84% of FSS. Over 24 h, a 4% FSS drift was observed.

CONCLUSION

Sensing system characteristics, coupled with low-cost, customizable fabrication, indicates promising performance for daily use to notify and alert transtibial prosthetic users of downward movement and/or pistoning.

Adjustable prosthetic sockets: a systematic review of industrial and research design characteristics and their justifications

BACKGROUND

The prosthetic socket is a key component that influences prosthesis satisfaction, with a poorly fitting prosthetic socket linked to prosthesis abandonment and reduced community participation. This paper reviews adjustable socket designs, as they have the potential to improve prosthetic fit and comfort through accommodating residual limb volume fluctuations and alleviating undue socket pressure.

METHODS

Systematic literature and patent searches were conducted across multiple databases to identify articles and patents that discussed adjustable prosthetic sockets. The patents were used to find companies, organisations, and institutions who currently sell adjustable sockets or who are developing devices.

RESULTS

50 literature articles and 63 patents were identified for inclusion, representing 35 different designs used in literature and 16 commercially available products. Adjustable sockets are becoming more prevalent with 73% of publications (literature, patents, and news) occurring within the last ten years. Two key design characteristics were identified: principle of adjustability (inflatable bladders, moveable panels, circumferential adjustment, variable length), and surface form (conformable, rigid multi-DOF, and rigid single DOF). Inflatable bladders contributed to 40% of literature used designs with only one identified commercially available design (n = 16) using this approach. Whereas circumferential adjustment designs covered 75% of identified industry designs compared to only 36% of literature devices. Clinical studies were generally small in size and only 17.6% of them assessed a commercially available socket.

DISCUSSION

There are clear differences in the design focus taken by industry and researchers, with justification for choice of design and range of adjustment often being unclear. Whilst comfort is often reported as improved with an adjustable socket, the rationale behind this is not often discussed, and small study sizes reduce the outcome viability. Many adjustable sockets lack appropriate safety features to limit over or under tightening, which may present a risk of tissue damage or provide inadequate coupling, affecting function and satisfaction. Furthermore, the relationship between design and comfort or function are rarely investigated and remain a significant gap in the literature. Finally, this review highlights the need for improved collaboration between academia and industry, with a strong disconnect observed between commercial devices and published research studies.

Assessing Socket Fit Effects on Pressure and Shear at a Transtibial Residuum/Socket Interface

Fluctuations in residuum volume during daily activities are known to occur in lower-limb amputees. This can cause frequent changes to fit, which cannot be accommodated by commonly-used prosthetic sockets. The real-time effects, if any, of these minor socket fit changes on interface biomechanics have not been studied extensively. Amputees commonly use different layers of socks to accommodate frequent volume fluctuations, enabling adjustment of socket fit. We, thus, altered socket fit levels via addition/removal of sock layers to a transtibial amputee who habitually-donned two-sock layers to mimic relatively looser and tighter socket fits. Interface pressure and shear sensors were placed at known prominent load-bearing sites of the transtibial residuum/socket interface, i.e., patellar tendon (PT), popliteal fossa (PF), and anterior-distal (AD) end, to measure real-time biomechanical interactions during standing and level walking. Although socket fit level was only slightly modified, changes in interface pressure and shear across anatomical sites were still observed. Tighter fit corresponds to notable pressure reduction at AD during early stance and pressure increase at PT during terminal stance due to the residuum being pushed up. Shear-to-pressure ratios were used to assess comfort, while pressure- and shear-time integrals were used to assess tissue health. We observed more notable changes at tissue sites (e.g., AD and PF). Combined evaluation of pressure and shear, including shear-to-pressure ratio and time integrals, may offer insight for residuum care.

Normalized kinematic walking symmetry data for individuals who use lower-limb prostheses: considerations for clinical practice and future research

Introduction

Individuals who use unilateral transtibial or transfemoral prostheses have negative secondary health effects associated with decreased kinematic (e.g., spatiotemporal and joint angle) walking symmetry between prosthetic and intact limbs. Research studies have quantified kinematic walking symmetry, but studies can be difficult to compare owing to the inclusion of small sample sizes and differences in participant demographics, biomechanical parameters, and mathematical analysis of symmetry. This review aims to normalize kinematic walking symmetry research data across studies by level of limb loss and prosthetic factors to inform considerations in clinical practice and future research.

Methods

A search was performed on March 18, 2020, in PubMed, Scopus, and Google Scholar to encompass kinematic walking symmetry literature from the year 2000. First, the most common participant demographics, kinematic parameters, and mathematical analysis of symmetry were identified across studies. Then, the most common mathematical analysis of symmetry was used to recalculate symmetry data across studies for the five most common kinematic parameters.

Results

Forty-four studies were included in this review. The most common participant demographics were younger adults with traumatic etiology who used componentry intended for higher activity levels. The most common kinematic parameters were step length, stance time, and sagittal plane ankle, knee, and hip range of motion. The most common mathematical analysis was a particular symmetry index equation.

Conclusions

Normalization of data showed that symmetry tended to decrease as level of limb loss became more proximal and to increase with prosthetic componentry intended for higher activity levels. However, most studies included 10 or fewer individuals who were active younger adults with traumatic etiologies.

Clinical Relevance

Data summarized in this review could be used as reference values for rehabilitation and payer justification. Specifically, these data can help guide expectations for magnitudes of walking symmetry throughout rehabilitation or to justify advanced prosthetic componentry for active younger adults under 65 years of age with traumatic etiologies to payers.

An Instrumented Printed Insert for Continuous Monitoring of Distal Limb Motion in Suction and Elevated Vacuum Sockets

A suction or elevated vacuum prosthetic socket that loses vacuum pressure may cause excessive limb motion, putting the user at risk of skin irritation, gait instability and injury. The purpose of this research was to develop a method to monitor distal limb motion and then test a small group of participants wearing suction sockets to identify variables that strongly influenced motion. A thin plastic insert holding two inductive sensor antennae was designed and printed. Inserts were placed in suction sockets made for four participants who regularly used suction or elevated vacuum suspension. Participants wore a liner with a trace amount of iron powder in the elastomer that served as a distance target for the sensors. In-lab testing demonstrated that the sensed distance increased when participants added socks and decreased when they removed socks, demonstrating proper sensor performance. Results from take-home testing (3–5 days) suggest that research investigation into cyclic limb motion for sock presence v. absence should be pursued, as should the influence of bodily position between bouts of walking. These variables may have an important influence on suspension. Long-term monitoring may provide clinical insight to improve fit and to enhance suction and elevated vacuum technology.

Using magnetic panels to enlarge a transtibial prosthetic socket

A novel method is described to connect a prosthetic liner to the panels of an adjustable socket to facilitate limb fluid volume stabilization in prosthesis users. Magnets are placed in the socket panels, and iron powder is embedded in the user's prosthetic liner. When the magnet is in close proximity to the liner, a firm connection is formed. The system's capability to execute panel pull on transtibial prosthesis users was tested. The backs of the panels were supported by a bracket mounted to the external surface of the socket that allowed the radial position of the panels to be adjusted. Bench testing demonstrated an optimized strength-to-weight ratio using 1.27-cm thick annular-shaped magnets supported by 0.32-cm thick backplates. Testing on four people with transtibial amputation showed that the maximum socket increase achieved using magnetic panel pull ranged from 5.3% to 13.8% of the initial (panels flush) socket volume. The results indicate that magnetic panel pull induces a meaningful increase in socket volume during sitting. The clinical relevance is a novel strategy that may help stabilize prosthesis users' limb fluid volume over the day.

A review of user needs to drive the development of lower limb prostheses

Background

The development of bionic legs has seen substantial improvements in the past years but people with lower-limb amputation still suffer from impairments in mobility (e.g., altered balance and gait control) due to significant limitations of the contemporary prostheses. Approaching the problem from a human-centered perspective by focusing on user-specific needs can allow identifying critical improvements that can increase the quality of life. While there are several reviews of user needs regarding upper limb prostheses, a comprehensive summary of such needs for those affected by lower limb loss does not exist.

Methods

We have conducted a systematic review of the literature to extract important needs of the users of lower-limb prostheses. The review included 56 articles in which a need (desire, wish) was reported explicitly by the recruited people with lower limb amputation (N = 8149).

Results

An exhaustive list of user needs was collected and subdivided into functional, psychological, cognitive, ergonomics, and other domain. Where appropriate, we have also briefly discussed the developments in prosthetic devices that are related to or could have an impact on those needs. In summary, the users would like to lead an independent life and reintegrate into society by coming back to work and participating in social and leisure activities. Efficient, versatile, and stable gait, but also support to other activities (e.g., sit to stand), contribute to safety and confidence, while appearance and comfort are important for the body image. However, the relation between specific needs, objective measures of performance, and overall satisfaction and quality of life is still an open question.

Conclusions

Identifying user needs is a critical step for the development of new generation lower limb prostheses that aim to improve the quality of life of their users. However, this is not a simple task, as the needs interact with each other and depend on multiple factors (e.g., mobility level, age, gender), while evolving in time with the use of the device. Hence, novel assessment methods are required that can evaluate the impact of the system from a holistic perspective, capturing objective outcomes but also overall user experience and satisfaction in the relevant environment (daily life).

Mechanically and physiologically optimizing prosthetic elevated vacuum systems in people with transtibial amputation: a pilot study

Introduction

The most suitable elevated vacuum (EV) pressure may differ for each individual prosthesis user depending on suspension needs, socket fit, prosthetic components, and health. Mechanical and physiological effects of EV were evaluated in an effort to determine the optimal vacuum pressure for three individuals.

Methods

Instrumented EV sockets were created based on the participants' regular EV sockets. Inductive distance sensors were embedded into the wall of the socket at select locations to measure limb movement relative to the socket. Each participant conducted an activity protocol while limb movement, limb fluid volume, and user-reported comfort were measured at various socket vacuum pressure settings.

Results

Increased socket vacuum pressure resulted in reduced limb-socket displacement for each participant; however, 81-93% of limb movement was eliminated by a vacuum pressure setting of 12 (approximately -9 inHg). Relative limb-socket displacement by sensor location varied for each participant, suggesting distinct differences related to socket fit or residual limb tissue content. The rate of limb fluid volume change and the change in socket comfort did not consistently differ with socket vacuum pressure, suggesting a more complex relationship unique to each individual.

Conclusions

Practitioners may use individual responses to optimize socket vacuum pressure settings, balancing mechanical and physiological effects of EV for improved clinical outcomes.

Reliability of three different methods for assessing amputee residuum shape and volume: 3D scanners vs. circumferential measurements

BACKGROUND

Objective and reliable methods are necessary to monitor and manage amputee residuum shape and volume and design prosthetic residuum-prosthesis interfaces. Portable 3D scanners are potential solutions for digitally recording the amputee residuum characteristics.

OBJECTIVE

To investigate test-operator reliability when measuring lower limb residuum shape and volume using two different types of 3D laser-free scanners compared with tape measurements generally adopted in clinic.

STUDY DESIGN

Ten lower limb amputees took part in this study. Residuum volume, cross sectional areas, and perimeter lengths were measured by three different operators on three different occasions using two types of 3D scanners (Artec Eva scanner and OMEGA Scanner 3D) and circumferential measurements.

METHODS

Variance components, intraclass correlation coefficients and intra-rater and inter-rater reliability coefficients were calculated for all measurement conditions.

RESULTS

Residuum volume outputs ranged from 569 to 3115 mL. The factor contributing mostly to the residuum volume error variance was the shape of the residuum (75.85%). Volume intraclass correlation coefficients for both intra-rater and inter-rater reliability exceeded 0.9 for all three conditions. Volume reliability coefficients ranged from 70.68 mL (Artec Eva intra-rater reliability) to 256.85 mL (circumferential measurements inter-rater reliability). Shape relative error reached the highest values for the circumferential measurements (>10% for the cross-sectional areas and >5% for the perimeters).

CONCLUSIONS

The Artec Eva scanner resulted in the lowest test-operator reliability coefficients. However, both investigated scanners are a potential alternative for measuring small and macroscopic changes in residuum characteristics.

Air microfluidics-enabled soft robotic transtibial prosthesis socket liner toward dynamic management of residual limb contact pressure and volume fluctuation

Residual limb volume fluctuation and the resulting contact pressures are some of the key factors leading to skin ulcerations, suboptimal prosthetic functioning, pain, and diminishing quality of life of transtibial amputees. Self-management of socket fit is complicated by peripheral neuropathy, reducing the perception of pressure and pain in the residual limb. We introduce a novel proof-of-concept for a transtibial prosthetic socket liner with the potential to dynamically adjust the fit between the limb and socket. The core of the technology is a small air microfluidic chip (10 cm³ and 10 g) with 10 on-chip valves that enable sequential pressurizing of 10 actuators in custom sizes to match the pressures required by the residual limb's unique anatomy. The microfluidic chip largely reduced the number of electromechanical solenoid valves needed for sequential control of 10 actuators (2 instead of 10 valves), resulting in the reduction of the required power, size, mass, and cost of the control box toward an affordable and wearable prosthetic socket. Proof-of-concept testing demonstrated that the applied pressures can be varied in the desired sequence and to redistribute pressure. Future work will focus on integrating the system with biofidelic prosthetic sockets and residual limb models to investigate the ability to redistribute pressure away from pressure-sensitive regions (e.g., fibular head) to pressure tolerant areas. Overall, the dynamic prosthesis socket liner is very encouraging for creating a dynamic socket fit system that can be seamlessly integrated with existing socket fabrication methods for managing residual limb volume fluctuations and contact pressure.

Scoping review to evaluate existing measurement parameters and clinical outcomes of transtibial prosthetic alignment and socket fit

INTRODUCTION

Fit and alignment are observable objectives of the prosthesis rendering process for individuals with lower limb amputation. Nevertheless, there is a dearth of validated measures to directly assess the quality of this clinical procedure.

OBJECTIVES

The objectives of this scoping review are to evaluate existing measurement parameters and clinical outcomes used in investigations of transtibial socket fit or prosthetic alignment and to identify gaps in the literature regarding tools for evaluation of prosthetic fitting.

STUDY DESIGN

Scoping literature review.

METHODS

A comprehensive search was conducted in the following databases: MEDLINE (through PubMed), Embase (through Elsevier), Scopus (through Elsevier), and Engineering Village (through Elsevier), resulting in 6107 studies to be screened.

RESULTS

Sixty-three studies were included in the review. When measuring fit, studies most frequently reported on patient-reported comfort (n = 22) and socket size compared with the residual limb volume (n = 9). Alignment was most frequently measured by the prosthetists' judgment and/or use of an alignment jig (n = 34). The measurement parameters used to determine alignment or fit varied greatly among the included studies.

CONCLUSION

This review demonstrated that most measures of socket fit rely on a patient's self-report and may vary with biopsychosocial factors unrelated to the socket fitting process. Meanwhile, alignment is determined mostly by the prosthetist's judgment, paired with objective measurements, such as alignment jigs and gait analysis. Efforts to standardize and validate measures of these parameters of prosthetic fitting are vital to improving clinical practice and reporting outcomes.

Effects of a modified passive socket system on short-term changes in residuum volume and comfort: A preliminary study in transtibial amputees

BACKGROUND

Changes in residuum volume are a common problem in lower-limb amputees during prosthesis usage, and can lead to poor suspension, impaired gait, and tissue damage. Residuum volume can be affected by the in-socket air pressure, which will influence fluid flow in and around the residuum. The use of "active" pumps to reduce air pressure has been shown to conserve the residuum volume, but these are expensive and unlikely to be widely available. An alternative, passive approach, based on Boyles' law, is to introduce a larger distal void volume at the end of the socket and hence reduce the change in pressure for a given change in volume.

OBJECTIVES

To compare the performance across three test conditions (passive-conventional, with standard distal void; passive-with increased distal void; and active system) in terms of residuum volume changes and comfort.

STUDY DESIGN

Repeated-measures experiment under three test conditions.

METHODS

Five transtibial amputee participants (three males and two females), aged between 27 and 67 years, and of mobility grade K2 or K3, were fitted with a bespoke test prosthesis that was adapted to include the three test conditions. Residuum volume was measured before and after walking under each test condition (presented in a random order). Comfort was also assessed after walking with each test condition.

RESULTS

The reduction in residuum volume, relative to the baseline volume, was higher for the conventional passive system (4.2% ± 2.8%) compared with the modified passive (1.4% ± 1.4%) and active (1.6% ± 1.1%) systems.

CONCLUSION

The use of a passive suspension system with an increased distal void within the socket may help to stabilize the residuum volume during prosthesis usage.

Design of lower limb prosthetic sockets: a review

INTRODUCTION

The prosthetic socket is the connecting part between the stump and the prosthesis, which is the important basis for the function of the prosthesis. The current prosthetic socket is difficult in meeting the needs of amputees current, which is the main reason for amputees abandoning their prostheses. This paper reviews the design and use of prosthetic sockets for lower limb.

AREAS COVERED

The contribution of this publication is to review the skin problem, interface stress and volume fluctuations for prosthetic sockets, which are proposed as the key factors affecting the use of prosthetic sockets. Moreover, the lower limb prosthetic sockets are classified into the full-contact and the frame-type sockets according to the different contact type between stump and prosthetic socket, and their advantages and disadvantages are analyzed from different perspectives.

EXPERT OPINION

Aim to design the prosthetic socket with function transfer, suspension stability and comfort of socket, a design concept for prosthetic socket with self-adapt in real-time is proposed. It can be achieved by the smart materials with special mechanical properties.

Deleterious Musculoskeletal Conditions Secondary to Lower Limb Loss: Considerations for Prosthesis-Related Factors

Significance: The intent of this work was to summarize the existing evidence of, and highlight knowledge gaps specific to, prosthetic devices/componentry and training regimes, particularly in the context of the human-device interaction and deleterious musculoskeletal conditions secondary to lower limb loss. Recent Advances: With the recent and evolving technological advancements in prostheses, there are numerous devices available to individuals with lower limb loss. Current literature demonstrates the importance of expanding the knowledge of all prosthetic device-specific factors and the significance of proper prescription, fit, and alignment, along with adequate device-/activity-specific training, to enhance human-device interaction, reduce gait abnormalities and compensatory motions, and as a result, mitigate risk for secondary musculoskeletal conditions. Critical Issues: Inadequate device prescription, fit, alignment, and training are evident owing to the lack of knowledge or awareness of the many device-specific properties and factors, leading to suboptimal use, as well as, biomechanical compensations, which collectively and adversely affect the function, activity level, and overall health of the prosthesis user. Future Directions: To maximize optimal outcomes after lower limb loss, it is essential to better appreciate the factors that affect both prosthesis use and satisfaction, particularly any modifiable factors that might be targeted in rehabilitation interventions such as device prescription, fit/alignment, and training regimes. A better understanding of such device-specific factors will help enhance the human-device interaction and resulting functional performance, thereby reducing secondary musculoskeletal conditions, allowing for the readiness of the fighting force (return-to-duty/redeployment) and/or improved reintegration into civilian society/work, and overall enhancing quality of life after lower limb loss.

Effects of Unity Prosthetic Elevated Vacuum Suspension System on Minimum Swing Toe Clearance

BACKGROUND

The risk of tripping in people with amputation is greater than that of able-bodied individuals due to reduced toe clearance during the swing phase. Appropriate prosthetic suspension may increase toe clearance by providing more secured attachment between the residual limb and prosthetic socket. Research is lacking on the Unity suspension system's effect on swing toe clearance.

METHODS

Twelve people with transtibial amputation were fitted with the Unity suspension system. After one month accommodation period, the person walked with active (ON) or inactive vacuum (OFF) in a CAREN-Extended virtual reality system, across multiple simulated real-world scenarios. Prosthetics minimum swing toe clearance, and kinematic data, while the vacuum was ON or OFF, were compared with the intact side and a group of 12 able-bodied individuals.

RESULTS

Minimum swing toe clearance (MSTC) and knee flexion angle were larger on the prosthetic side (active and inactive vacuum) compared to both the intact side and the control group. However, hip flexion angle on the prosthetic side was approximately 17% smaller than the control group. Unlike the control group, MSTC with active and inactive vacuum suspension was not significantly different between level walking and other walking conditions. Finally, among all walking conditions, the lowest swing toe clearance for both control and the amputee groups was recorded when the limb was at the top of a side-slope.

CONCLUSION

An effective suspension system could improve toe clearance; however, significant differences were not found between active and inactive vacuum conditions. The likelihood of inappropriate foot contact on side-slope ground might be greater than other walking conditions for both able-bodied and amputee groups, possibly leading to stumbling or falling.

Effect of transfemoral prosthetic socket interface design on gait, balance, mobility, and preference: A randomized clinical trial

BACKGROUND

There are alternative transfemoral (TF) socket interface designs that have not been compared with the standard of care, ischial ramus containment (IRC). The interface directly affects performance.

OBJECTIVES

To compare 3 TF interface designs, IRC, dynamic socket (DS), and subischial (Sub-I), regarding gait, balance, mobility, and preference. The authors hypothesized that these more active users may experience gait, mobility, and preference benefits from the less intrusive DS and Sub-I interface designs.

STUDY DESIGN

Single-blind, repeated-measures, 3-period randomized controlled crossover clinical trial.

METHODS

People with unilateral TF amputation with 1 year or longer prosthesis use experience, independent community ambulatory status, 18 to 60 years of age, of any race or ethnicity, with a body mass of 45 to 125 kg, and with a self-reported ability to walk for 20 minutes continuously were included in the study. Each participant was fit in all 3 interface designs.

RESULTS

Thirteen participants completed the clinical trial. Velocity, cadence, mobility, and balance were not statistically different between the 3 socket conditions. The DS demonstrated significantly greater symmetry in swing, stance, single support percentage, and toe angle compared with IRC and Sub-I. Sixty days after study completion, 7 participants changed interfaces, trending away from IRC.

CONCLUSIONS

Large differences were not observed. Small differences in spatiotemporal gait measures combined with patient preference may make a meaningful difference to individual patients and should be considered.

Residual limb volume fluctuations in transfemoral amputees

This study constitutes the first attempt to systematically quantify residual limb volume fluctuations in transfemoral amputees. The study was carried out on 24 amputees to investigate variations due to prosthesis doffing, physical activity, and testing time. A proper experimental set-up was designed, including a 3D optical scanner to improve precision and acceptability by amputees. The first test session aimed at measuring residual limb volume at 7 time-points, with 10 min intervals, after prosthesis doffing. This allowed for evaluating the time required for volume stabilization after prosthesis removal, for each amputee. In subsequent sessions, 16 residual limb scans in a day for each amputee were captured to evaluate volume fluctuations due to prosthesis removal and physical activity, in two times per day (morning and afternoon). These measurements were repeated in three different days, a week apart from each other, for a total of 48 scans for each amputee. Volume fluctuations over time after prosthesis doffing showed a two-term decay exponential trend (R2 = 0.97), with the highest variation in the initial 10 min and an average stabilization time of 30 min. A statistically significant increase in residual limb volume following both prosthesis removal and physical activity was verified. No differences were observed between measures collected in the morning and in the afternoon.Clinical Trials.gov ID: NCT04709367.

Socket release/relock: An innovative mechanism to maintain residual limb volume

Management of socket fit is challenging for people using lower-limb prostheses because of residual limb volume fluctuation throughout the day. Releasing socket pressures during sitting (partial doffing) may help users increase their limb volume after they have undergone volume loss earlier in the day. The purpose of this research was to develop and evaluate a system to allow for quick and easy locking pin and socket panel release during sitting and relock upon standing. The system was to allow the partial doff tether length to be custom set for each user, accomplish release and relock in less than 2.0 s each, require only one hand, and require a finger push force comparable to a push button on a phone. A motor-driven release/relock system (<240 g build weight) housed within the socket adjusts locking pin tether length, and an instrumented ratcheting dial adjusts socket panel position. Three participants with a trans-tibial amputation operated the system properly using one hand. For a partial doff, users preferred a tether length between 5 and 6 cm. All users executed release within 1.5 s and relock within 1.5 s.

Physical sciences

In the original edition of Prosthetics and Orthotics International, Dr Sidney Fishman identified what he anticipated as foundational educational needs for the emerging field of clinical prosthetics and orthotics. Within the broader construct of the physical sciences, this included mathematics, physics, chemistry, biomechanics, and material sciences. The clinical application of these disciplines to expanding the collective understanding within the field is described, including the biomechanics of able-bodied and prosthetic gait, the material science of socket construction, the physics of suspension and load distribution, and the engineering of prosthetic components to mimic human biomechanics. Additional applications of the physical sciences to upper limb prosthetics and lower limb orthotics are also described. In contemplating the continued growth and maturation of the field in the years to come, mechatronics and statistics are suggested as future areas where clinical proficiency will be required.

Lower limb prosthetic interfaces: Clinical and technological advancement and potential future direction

The human-prosthesis interface is one of the most complicated challenges facing the field of prosthetics, despite substantive investments in research and development by researchers and clinicians around the world. The journal of the International Society for Prosthetics and Orthotics, Prosthetics and Orthotics International, has contributed substantively to the growing body of knowledge on this topic. In celebrating the 50th anniversary of the International Society for Prosthetics and Orthotics, this narrative review aims to explore how human-prosthesis interfaces have changed over the last five decades; how research has contributed to an understanding of interface mechanics; how clinical practice has been informed as a result; and what might be potential future directions. Studies reporting on comparison, design, manufacturing and evaluation of lower limb prosthetic sockets, and osseointegration were considered. This review demonstrates that, over the last 50 years, clinical research has improved our understanding of socket designs and their effects; however, high-quality research is still needed. In particular, there have been advances in the development of volume and thermal control mechanisms with a few designs having the potential for clinical application. Similarly, advances in sensing technology, soft tissue quantification techniques, computing technology, and additive manufacturing are moving towards enabling automated, data-driven manufacturing of sockets. In people who are unable to use a prosthetic socket, osseointegration provides a functional solution not available 50 years ago. Furthermore, osseointegration has the potential to facilitate neuromuscular integration. Despite these advances, further improvement in mechanical features of implants, and infection control and prevention are needed.

Sustainable, affordable and functional: reimagining prosthetic liners in resource limited environments

PURPOSE

The purpose of this study was to evaluate function and performance of unilateral trans-tibial prosthesis users wearing an affordable liner in three types of socket designs.

METHODS

Five unilateral trans-tibial amputees participated, were provided an Affordable Ethyl-Vinyl-Acetate Roll-On liner (AERO) roll-on liner with patella tendon bearing (PTB) prosthesis, PE-Lite liner with PTB prosthesis, and an (AERO) liner with total-surface bearing (TSB) prosthesis. A battery of outcome measures; step-counts, socket comfort score (SCS), orthotics prosthetics user survey (OPUS) and socket pressure measurement during walking were administered.

RESULTS

Comparisons of step-counts indicated that PTB-AERO (3604 ± 815) was not significantly different than PTB-PE-Lite (3386 ± 942). Mean SCS was 9.2 ± .83 and 7.2 ± 2.1 for PTB-AERO and PTB-PE-Lite. A 6.6% decrease in mean peak pressure was observed between PTB-PE-Lite and TSB-AERO, and 3.2% difference between PTB-PE-Lite and PTB-AERO.

CONCLUSION

An affordable ($20 USD) and sustainably fabricated prosthesis liner was created and evaluated in trans-tibial prosthesis users. These initial results garner preliminary support for use of the AERO prosthetic liner and continued research.Implications for rehabilitationLower limb prosthetics in less-resourced settings can leverage locally sourced and affordable materials to fabricate roll-on liners for use in modern prosthetic sockets.The cost of the AERO liner is markedly lower than current standard of care gel liners, yet still facilitates use of current prosthetic sockets.

Quality of life, body image, and mobility in lower-limb amputees using high-tech prostheses: A pragmatic trial

BACKGROUND

High-tech prostheses are supposed to achieve better functional recovery over mechanical-controlled prostheses in lower-limb amputees. However, quantitative data are insufficient.

OBJECTIVE

We aimed to evaluate changes in quality of life, life satisfaction, perception of body image, and functional performance of lower-limb amputees when using a mechanical-controlled prosthesis versus a microprocessor-controlled knee (MPK) or transtibial vacuum-assisted suspension system (VASS) prosthesis.

METHODS

In this pragmatic study, 57 lower-limb amputees were assessed with the Satisfaction with the Prosthesis Questionnaire (SATPRO), revised Amputee Body Image Scale (ABIS-R), Trinity Amputation and Prosthesis Experience Scales (TAPES), Medical Outcomes Study Short Form-36 (SF-36) and 6-min walk test (6MWT). All assessments were performed under 2 conditions (i.e., using a mechanical-controlled prosthesis vs. an MPK/VASS prosthesis.

RESULTS

Amputees who used an MPK/VASS prosthesis showed significant increases in all SF-36 subscale scores and all subscale scores of TAPES except adjustment to limitation (P=0.156). The amputees showed clinically relevant improvements in 6MWT (P<0.001) and in SATPRO and ABIS-R scores (P<0.001).

CONCLUSION

Lower-limb amputees using an MPK/VASS prosthesis had better life satisfaction, quality of life and functional performance than those using a mechanical-controlled prosthesis.

Modeling the mechanics of elevated vacuum systems in prosthetic sockets

Elevated vacuum (EV) is suggested to improve suspension and limb volume management for lower limb prosthesis users. However, few guidelines have been established to facilitate configuration of EV sockets to ensure their safe and proper function. A benchtop model of an EV socket was created to study how prosthetic liner tensile elasticity, socket fit, and socket vacuum pressure affect liner displacement and subsequent pressure on the residual limb. A domed carbon fiber layup was used to represent an EV socket. Inserts were used to simulate various air gaps between the socket and liner. Various prosthetic liner samples were placed under the carbon fiber layup. Liner displacement and the corresponding pressure change underneath the liner were measured as vacuum was applied between the liner sample and socket wall. Tissue vacuum pressure increased linearly with socket vacuum pressure until the liner contacted the socket wall. Predicted tissue vacuum pressure matched well with experimental results. Findings suggest that the effect of vacuum pressure on the residual limb is primarily determined by air gap distance. The developed model may be used to assess effects of EV on residual limb tissues based on an individual's socket fit, liner characteristics, and applied vacuum. Understanding the physiological effects of EV on the residual limb could help practitioners avoid blister formation and improve EV implementation.

Using mechanical testing to assess the effect of lower-limb prosthetic socket texturing on longitudinal suspension

To function effectively, a lower limb prosthetic socket must remain securely coupled to the residual limb during walking, running and other activities of daily living; this coupling is referred to as suspension. When this coupling is insufficient longitudinal pistoning of the socket relative to the residual limb occurs. Increasing friction of the socket/liner interface may improve socket suspension and textured sockets may be fabricated relatively easily with 3D printing. The aim of this study was to investigate longitudinal displacement of sockets with different types of textures under two suspension conditions: passive suction and active vacuum. In order to do this, we developed a mock residual limb and mechanical testing protocol. Prosthetic sockets, 14 textured sockets and an Original Squirt-Shape (OSS) Socket, were fabricated from polypropylene copolymer using the Squirt-Shape^™ 3D Printer and compared to a smooth socket thermoformed from polypropylene copolymer. Sockets were mounted onto a dual durometer mock residual limb and subjected to four levels of distraction forces (100 N, 250 N, 500 N and 650 N) using a hydraulic material testing system. There was a statistically significant three-way interaction between suspension, force level and texture (p < 0.0005). Longitudinal displacements between textured and reference sockets, for all force levels and both suspension conditions, were significantly different (p < 0.0005). Using these newly developed mechanical testing protocols, it was demonstrated that texturing of polypropylene copolymer sockets fabricated using Squirt-Shape significantly decreased longitudinal displacements compared to a smooth socket. However, none of the novel textured sockets significantly reduced longitudinal displacement compared to the OSS socket under passive suction suspension.

Does actively enlarging socket volume during resting facilitate residual limb fluid volume recovery in trans-tibial prosthesis users?

BACKGROUND

Residual limb volume loss is a source of prosthetic socket fit problems in people with lower-limb amputation. The aim of this study was to investigate a novel volume recovery strategy for people with trans-tibial amputation.

METHODS

Test sockets for people with trans-tibial amputation were created that allowed panels of an adjustable socket and the underlying elastomeric liner to be pulled radially outward, using small motors mounted to the socket. One Control and one Intervention session were conducted with each participant. During Intervention sessions, panel-pull was executed during the sits of a multi-cycle sit/walk protocol. No panel-pull was executed during the Control sessions. Residual limb fluid volume was monitored in anterior and posterior regions using bioimpedance analysis.

FINDINGS

Results from 12 participants demonstrated that short-term (12 min after the intervention was applied) median posterior residual limb fluid volume change for Intervention (0.44%) was higher than that for Control (-0.02%) (P = .015). Long-term (40 min after the intervention was applied) median posterior residual limb fluid volume change for Intervention (0.95%) was higher than that for Control (-0.26%) (P = .002).

INTERPRETATION

If a panel-pull mechanism that was easy to assemble and operate could be created, then panel-pull may be an effective accommodation strategy to reduce daily limb volume loss in trans-tibial prosthesis users.

Effectiveness of elevated vacuum and suction prosthetic suspension systems in managing daily residual limb fluid volume change in people with transtibial amputation

BACKGROUND

Previous studies investigating limb volume change with elevated vacuum have shown inconsistent results and have been limited by out-of-socket volume measurements and short, single-activity protocols.

OBJECTIVES

To evaluate the effectiveness of elevated vacuum for managing limb fluid volume compared to suction suspension with an in-socket measurement modality during many hours of activity.

STUDY DESIGN

Fixed-order crossover design with a standardized out-of-laboratory activity protocol.

METHODS

Transtibial electronic elevated vacuum users participated in two sessions. Elevated vacuum was used during the first session, and suction suspension in the second. Participants completed a 5.5-h protocol consisting of multiple intervals of activity. In-socket residual limb fluid volume was continuously measured using a custom portable bioimpedance analyzer.

RESULTS

A total of 12 individuals participated. Overall rate of fluid volume change was not significantly different, though the rate of posterior fluid volume change during Cycle 3 was significantly lower with elevated vacuum. Although individual results varied, 11 participants experienced lower overall rates of fluid volume loss in at least one limb region using elevated vacuum.

CONCLUSION

Elevated vacuum may be more effective as a volume management strategy after accumulation of activity. Individual variation suggests the potential to optimize the limb fluid volume benefits of elevated vacuum by reducing socket vacuum pressure for some users.

CLINICAL RELEVANCE

A better understanding of how elevated vacuum (EV) affects residual limb fluid volume will allow prosthetists to make more informed clinical decisions regarding accommodation strategies designed to improve daily socket fit.

Fluid Volume Management in Prosthesis Users: Augmenting Panel Release with Pin Release

BACKGROUND

Management of fluid in the limbs is a challenge faced by people with disabilities. In prosthetics, a means for transtibial prosthesis users to stabilize their residual limb fluid volume during the day may improve socket fit.

OBJECTIVE

To determine if releasing the panels and locking pin of a cabled-panel adjustable socket during socket release significantly improved limb fluid volume recovery and retention over releasing the panels alone.

DESIGN

Repeated-measures experiment to assess the effects on limb fluid volume retention.

SETTING

Participants were tested in a laboratory setting while walking on a treadmill.

INTERVENTION

Release of a locking pin tether during sitting as a limb volume accommodation strategy.

MAIN OUTCOME MEASURE

Percent limb fluid volume retention for panel and pin release compared with panel release alone at 2 minutes (short term) and 50 minutes (long term) after subsequent activity. Limb fluid volume was monitored using bioimpedance analysis.

RESULTS

Median percent limb fluid volume retention for the panel and pin release was significantly greater than panel release alone for both anterior and posterior regions for the long term (P = .0499 and .0096, respectively) but not the short term (P = .0712 and .1580, respectively).

CONCLUSION

Augmenting panel release with pin release may be an effective accommodation strategy for prosthesis users with transtibial amputation to better retain limb fluid volume.

Sensing and actuation technologies for smart socket prostheses

The socket is the most critical part of every lower-limb prosthetic system, since it serves as the interfacial component that connects the residual limb with the artificial system. However, many amputees abandon their socket prostheses due to the high-level of discomfort caused by the poor interaction between the socket and residual limb. In general, socket prosthesis performance is determined by three main factors, namely, residual limb-socket interfacial stress, volume fluctuation of the residual limb, and temperature. This review paper summarizes the various sensing and actuation solutions that have been proposed for improving socket performance and for realizing next-generation socket prostheses. The working principles of different sensors and how they have been tested or used for monitoring the socket interface are discussed. Furthermore, various actuation methods that have been proposed for actively modifying and improving the socket interface are also reviewed. Through the continued development and integration of these sensing and actuation technologies, the long-term vision is to realize smart socket prostheses. Such smart socket systems will not only function as a socket prosthesis but will also be able to sense parameters that cause amputee discomfort and self-adjust to optimize its fit, function, and performance.

Reported physical activity and quality of life in people with lower limb amputation using two types of prosthetic suspension systems

BACKGROUND

Vacuum-assisted suspension systems provide better suspension than non-vacuum systems, but data are limited on whether they improve physical activity levels and quality of life for people with amputation.

OBJECTIVES

To compare the physical activity and quality of life levels of people with transtibial amputation using PIN/LOCK suspension system or vacuum-assisted suspension systems with those of able-bodied controls and to investigate parameters associated with physical activity levels.

STUDY DESIGN

A cross-sectional observational study.

METHODS

Fifty-one people with amputation and 51 controls participated. The International Physical Activity Questionnaire Short Form and Short Form 36 were used to measure the physical activity and quality of life, respectively.

RESULTS

The total physical activity and Short Form 36 scores were significantly lower in the participants with amputation than the controls. There were no significant differences between the two types of suspension systems in terms of physical activity levels and quality of life. The vacuum-assisted suspension system users reported significantly more bodily pain on the Short Form 36 questionnaire than the controls (p = 0.003). The only parameter that correlated significantly with the total physical activity was the Short Form 36 physical functioning subscale (r = 0.302, p = 0.031).

CONCLUSION

Contrary to our expectations, vacuum-assisted suspension system users compared to PIN/LOCK users did not report greater levels of physical activity or improved quality of life or levels closer to comparable controls.

CLINICAL RELEVANCE

A better understanding of the effects of different prosthetic suspension systems on physical activity and quality of life may help clinicians when prescribing prostheses, as well as setting appropriate prosthetic expectations. This study suggests that vacuum-assisted suspension systems and PIN/LOCK suspension systems provide equal benefit to users with regards to physical activity and quality of life.

How do transtibial residual limbs adjust to intermittent incremental socket volume changes?

BACKGROUND

Strategies to maintain prosthesis users' daily limb volume are needed.

OBJECTIVES

Test how intermittent incremental socket volume adjustments affect limb fluid volume and limb-socket distance.

STUDY DESIGN

Repeated measures.

METHODS

People with transtibial limb loss walked on an outdoor trail wearing a motor-driven adjustable socket that they adjusted a small amount, approximately 0.3% socket volume, every 2 min using a mobile phone app. Limb fluid volume and sensed distance between the socket and a target in their elastomeric liner were monitored. A gradual socket enlargement phase was followed by a gradual socket reduction phase.

RESULTS

An incremental socket enlargement significantly increased limb fluid volume (p < 0.001) but not sensed distance (p = 0.063). An incremental socket reduction significantly decreased both limb fluid volume (p < 0.001) and sensed distance (p < 0.001).

CONCLUSION

Participants' residual limb fluid volume increases during ambulation compensated for incremental socket volume increases. For incremental socket volume decreases, residual limb fluid volume decreases did not compensate and the socket fit became tighter.

CLINICAL RELEVANCE

Results support the hypothesis that for people without co-morbidities, intermittent incremental socket volume enlargements are an effective accommodation strategy to increase limb fluid volume while maintaining socket fit. Intermittent incremental socket volume reductions decreased limb fluid volume but also made the socket fit tighter.

The development and internal consistency of the comprehensive lower limb amputee socket survey in active lower limb amputees

BACKGROUND:

Prosthetic socket fit is an important element associated with successful ambulation and use of a prosthesis. Prosthetists and rehabilitation clinicians would benefit from an assessment tool that discriminates between and quantifies the multiple determinants that influence the lower limb amputee's performance and satisfaction of a prosthetic socket.

OBJECTIVES:

To determine the internal consistency of the comprehensive lower limb amputee socket survey, a new self-report measure of prosthetic socket satisfaction that quantifies suspension, stability, comfort, and appearance.

STUDY DESIGN:

Cross-sectional sample of active amputees.

METHODS:

Interviews were conducted with prosthetists, physical therapists, and lower limb amputees to identify clinical concerns and common activities influencing socket fit. An expert panel of five clinicians reviewed the items and constructed the original version of the comprehensive lower limb amputee socket survey which was then administered to a convenience sample of 47 active lower limb amputees. Item analysis and Cronbach's alpha were used to determine the final version of the comprehensive lower limb amputee socket survey.

RESULTS:

Following item raw score-to-total score correlation with Cronbach's alpha for comprehensive lower limb amputee socket survey determinants, internal consistency improved when nine questions were eliminated.

CONCLUSION:

The comprehensive lower limb amputee socket survey is a self-report measure of prosthetic socket satisfaction with very good internal consistency.

CLINICAL RELEVANCE

When socket problems occur, the ability to determine the specific cause can reduce modification time, enhance socket fit, and promote patient satisfaction. A standardized multi-dimensional assessment measure of socket satisfaction enables prosthetists to quantify the multiple determinants of socket satisfaction, improve patient communication, and demonstrate the value of socket interventions.

Effects of activity intensity, time, and intermittent doffing on daily limb fluid volume change in people with transtibial amputation

BACKGROUND:

The volume of a prosthesis user's residual limb changes during the day and may affect the fit of the prosthesis. These changes must be managed by the user to prevent discomfort, skin breakdown, and falls.

OBJECTIVES:

The objectives were to test how activity, time of day, and intermittent doffing affected residual limb fluid volume in people with transtibial amputation.

STUDY DESIGN:

Standardized, repeated measure (A-B-A) out-of-laboratory protocol.

METHODS:

Participants with transtibial amputation completed three 6-h test sessions. Two sessions served as controls (A protocol) during which participants left their prosthesis donned, and one session was an intervention (B protocol) where participants doffed their prosthesis twice for 20 min during the 6 h of testing. Within-socket fluid volume was measured using a custom portable bioimpedance analysis system.

RESULTS:

A total of 13 participants completed the study. The rate of limb fluid volume loss was higher early in the session compared with late in the session. Participants experienced less fluid volume loss during high activity than low activity. Socket users with pin suspension experienced less posterior fluid volume loss when they intermittently doffed their prosthesis. Intermittent doffing did not benefit limb fluid volume of mechanical vacuum and suction suspension users.

CONCLUSION:

High activity may reduce fluid volume loss compared with low activity. Intermittent doffing may provide volume accommodation for transtibial prosthesis users with pin suspension.

CLINICAL RELEVANCE

Prosthetists should query their patients about the intensity of activity they conduct when advising them on limb volume management. Patients using sockets with pin suspension may be able to offset limb fluid volume loss by periodically doffing the prosthesis.

An Inductive Sensing System to Measure In-Socket Residual Limb Displacements for People Using Lower-Limb Prostheses

The objective of this research was to assess the performance of an embedded sensing system designed to measure the distance between a prosthetic socket wall and residual limb. Low-profile inductive sensors were laminated into prosthetic sockets and flexible ferromagnetic targets were created from elastomeric liners with embedded iron particles for four participants with transtibial amputation. Using insights from sensor performance testing, a novel calibration procedure was developed to quickly and accurately calibrate the multiple embedded sensors. The sensing system was evaluated through laboratory tests in which participants wore sock combinations with three distinct thicknesses and conducted a series of activities including standing, walking, and sitting. When a thicker sock was worn, the limb typically moved further away from the socket and peak-to-peak displacements decreased. However, sensors did not measure equivalent distances or displacements for a given sock combination, which provided information regarding the fit of the socket and how a sock change intervention influenced socket fit. Monitoring of limb⁻socket displacements may serve as a valuable tool for researchers and clinicians to quantitatively assess socket fit.

Real time monitoring of transtibial elevated vacuum prostheses: A case series on socket air pressure

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.

The functional, spatio-temporal and satisfaction outcomes of transtibial amputees with a hydrocast socket following an extended usage period in an under-resourced environment

BACKGROUND

Transtibial hydrocast sockets have been shown to be a potential alternative to hand-cast patella-tendon bearing sockets, the use of which would have particular benefits in under-resourced environments. However, data concerning wearer outcomes of hard hydrocast sockets (i.e. those without silicone liners), especially over long-term usage periods, is scarce in the literature.

RESEARCH QUESTIONS

Are there any changes in wearer functional, spatio-temporal or satisfaction outcomes over a long usage period with a hydrocast socket? And how do the post-usage period outcomes compare with those from the wearers original prostheses?

METHODS

In this pre-post interventional study, the clinical outcomes of twenty-one experienced transtibial prostheses users were evaluated using widely-accepted and employed methods to assess wearer functional capacity, mobility, gait and satisfaction. The participants were fit with a hard hydrocast socket and the outcomes after an extensive usage period of 5 months were compared to the pre-usage period data following initial fitting and the data collected from the participants' original prosthetic limb.

RESULTS

Significant differences were found in the temporal parameters of gait, all indicating decreased reliance on the intact limb and an increased loading of the prosthetic limb with the post-usage period hydrocast socket compared to both the pre-usage period socket and the participants' original limbs. No differences in the functional capacity, mobility, spatial gait parameters or satisfaction were found between the socket conditions.

SIGNIFICANCE

This is the largest study to date of functional, spatio-temporal and satisfaction outcomes of hydrocast sockets following an extended usage period in an under-resourced environment.

Transtibial amputee gait during slope walking with the unity suspension system

BACKGROUND

People with lower limb amputation may experience walking limitations on slopes because of missing musculoskeletal and neuromuscular systems. Elevated vacuum suspension could benefit transtibial amputee gait for slope walking, but research is lacking to inform clinical practice.

METHODS

Twelve people with unilateral transtibial amputation were fitted with the Unity elevated vacuum suspension system (Össur) and Pro-Flex XC foot. 3D motion analysis was performed for 7° incline, 7° decline, and level walking within a CAREN-Extended system virtual Park environment. Randomized and blinded walking trials were completed with the vacuum active or inactive.

RESULTS

Statistically significant differences (p < 0.05) were found between vacuum conditions when walking uphill or downhill for temporal spatial, kinematic, and kinetic gait parameters; however, effect sizes were small (r≤0.35). Prosthetic step length decreased for both vacuum conditions on downhill compared to uphill walking. Symmetry index was <10% for step length, step time, and stance time for both vacuum condition during downhill walking, indicating acceptable symmetry. During incline walking, step length was only symmetrical with active vacuum. Knee range of motion was not restricted, for both conditions.

CONCLUSION

Active vacuum improved gait symmetry for incline walking, but the other differences between vacuum conditions were small and may not be clinically significant. Therefore, the Unity system approach for elevated vacuum suspension had a positive, but small, effect on walking and should maintain appropriate walking even with vacuum failure, until limb volume changes adversely affect socket fit (i.e., elevated vacuum helps control limb volume fluctuations over time).

Systematic Experimental Assessment of a 2D-Motion Sensor to Detect Relative Movement between Residual Limb and Prosthetic Socket

A sensor system for measuring the relative movement between prosthetic socket and residual limb based on a 2D-motion sensor is introduced and thoroughly tested experimentally. The quantitative analysis of test rig evaluation is used to identify advantageous sensor settings and liner configurations. Considering these favorable settings, sensor functionality is quantified to errrel=0.52±1.78%. Advancing to convex measurement surfaces, the sensor shows absolute errors of errabs≤1 mm in an observable measurement scenario. The feasibility of measuring gait-induced relative movement with the proposed 2D-motion sensor is shown via a biomechanical plausibility study. Overall, the findings suggest that the proposed sensor system is suitable for investigating the relative movement between residual limb and prosthetic socket in dynamic gait situations.

Effects of the unity vacuum suspension system on transtibial gait for simulated non-level surfaces

Walking on various surfaces encountered in everyday life requires lower limb prosthesis users to continually adapt their movement patterns. Elevated vacuum suspension systems could improve transtibial amputee gait on non-level surfaces; however, research is lacking to guide clinical practice. Twelve transtibial amputees were fitted with the Össur sleeveless vacuum suspension system (Unity). After a one month accommodation period, the CAREN-Extended system was used to evaluate gait on a self-paced treadmill when walking with continuous perturbations (medial-lateral translations, rolling hills, simulated uneven ground) with an active or inactive vacuum suspension system. Significant differences between active and inactive vacuum conditions (p<0.05) were found for some temporal-spatial and kinematic gait parameters, but the differences were small and not considered clinically significant. Our findings suggest that potential vacuum pump failures would not immediately affect gait performance in a moderately high functioning amputee population. However, residual limb volume changes over time due to the removal of elevated vacuum may adversely affect socket fit, leading to greater gait differences and reduced quality of life.

A new method to quantify liner deformation within a prosthetic socket for below knee amputees

Many amputees who wear a leg prosthesis develop significant skin wounds on their residual limb. The exact cause of these wounds is unclear as little work has studied the interface between the prosthetic device and user. Our research objective was to develop a quantitative method for assessing displacement patterns of the gel liner during walking for patients with transtibial amputation. Using a reflective marker system and a custom clear socket, evaluations were conducted with a clear transparent test socket mounted over a plaster limb model and a deformable limb model. Distances between markers placed on the limb were measured with a digital caliper and then compared with data from the motion capture system. Additionally, the rigid plaster set-up was moved in the capture volume to simulate walking and evaluate if inter-marker distances changed in comparison to static data. Dynamic displacement trials were then collected to measure changes in inter-marker distance due to vertical elongation of the gel liner. Static and dynamic inter-marker distances within day and across days confirmed the ability to accurately capture displacements using this new approach. These results encourage this novel method to be applied to a sample of amputee patients during walking to assess displacements and the distribution of the liner deformation within the socket. The ability to capture changes in deformation of the gel liner will provide new data that will enable clinicians and researchers to improve design and fit of the prosthesis so the incidence of pressure ulcers can be reduced.

Elevated vacuum suspension preserves residual-limb skin health in people with lower-limb amputation: Randomized clinical trial

A growing number of clinical trials and case reports support qualitative claims that use of an elevated vacuum suspension (EVS) prosthesis improves residual-limb health on the basis of self-reported questionnaires, clinical outcomes scales, and wound closure studies. Here, we report first efforts to quantitatively assess residual-limb circulation in response to EVS. Residual-limb skin health and perfusion of people with lower-limb amputation (N = 10) were assessed during a randomized crossover study comparing EVS with nonelevated vacuum suspension (control) over a 32 wk period using noninvasive probes (transepidermal water loss, laser speckle imaging, transcutaneous oxygen measurement) and functional hyperspectral imaging approaches. Regardless of the suspension system, prosthesis donning decreased perfusion in the residual limb under resting conditions. After 16 wk of use, EVS improved residual-limb oxygenation during treadmill walking. Likewise, prosthesis-induced reactive hyperemia was attenuated with EVS following 16 wk of use. Skin barrier function was preserved with EVS but disrupted after control socket use. Taken together, outcomes suggest chronic EVS use improves perfusion and preserves skin barrier function in people with lower-limb amputation.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov; "Evaluation of limb health associated with a prosthetic vacuum socket system": NCT01839123; https://clinicaltrials.gov/ct2/show/NCT01839123?term=NCT01839123&rank=1.

Sockets for Limb Prostheses: A Review of Existing Technologies and Open Challenges

In the prosthetics field, one of the most important bottlenecks is still the human-machine interface, namely the socket. Indeed, a large number of amputees still rejects prostheses or points out a low satisfaction level, due to a sub-optimal interaction between the socket and the residual limb tissues. The aim of this paper is to describe the main parameters (displacements, stress, volume fluctuations and temperature) affecting the stump-socket interface and reducing the comfort/stability of limb prostheses. In this review, a classification of the different socket types proposed in the literature is reported, together with an analysis of advantages and disadvantages of the different solutions, from multiple viewpoints. The paper then describes the technological solutions available to face an altered distribution of stresses on the residual limb tissues, volume fluctuations affecting the stump overtime and temperature variations affecting the residual tissues within the socket. The open challenges in this research field are highlighted and the possible future routes are discussed, towards the ambitious objective of achieving an advanced socket able to self-adapt in real-time to the complex interplay of factors affecting the stump, during both static and dynamic tasks.

Development of a magnetic composite material for measurement of residual limb displacements in prosthetic sockets

INTRODUCTION

Wearable limb-socket displacement sensors may help patients and prosthetists identify a deteriorating socket fit and justify the need for repair or replacement.

METHODS

A novel sensor using an inductive sensing modality was developed to detect limb-to-socket distances. Key detection elements were a coil antenna placed in the socket wall and a magnetic composite sheath worn over the outside of the prosthesis user's elastomeric liner. The sheath was a nylon or cotton prosthetic stocking coated with a polyurethane composite. The polyurethane composite contained embedded iron particles (75 wt%).

RESULTS

Brushing γ-glycidoxypropyltriethoxysilane onto the sheath fabric, coating it first with unfilled polyurethane and then iron-filled polyurethane, enhanced bonding between the sheath and the composite and overcame mechanical degradation problems. A γ-glycidoxypropyltriethoxysilane-rich fumed silica layer applied to the outside of the sheath reduced friction and improved durability. Field testing demonstrated less than a 3% signal degradation from four weeks of field use.

CONCLUSIONS

The developed wearable displacement sensor meets durability and performance needs, and is ready for large-scale clinical testing.

Clinical evaluation of a prosthetic suspension system: Looped silicone liner

OBJECTIVES

This study aimed to evaluate and compare a newly designed suspension system with a common suspension in the market.

STUDY DESIGN

Prospective study.

METHODS

Looped liners with hook fastener and Iceross Dermo Liner with pin/lock system were mechanically tested using a tensile testing machine in terms of system safety. A total of 10 transtibial amputees participated in this study and were asked to use these two different suspension systems. The pistoning was measured between the liner and socket through a photographic method. Three static axial loading conditions were implemented, namely, 30, 60, and 90 N. Furthermore, subjective feedback was obtained.

RESULTS

Tensile test results showed that both systems could safely tolerate the load applied to the prosthesis during ambulation. Clinical evaluation confirmed extremely low pistoning in both systems (i.e. less than 0.4 cm after adding 90 N traction load to the prosthesis). Subjective feedback also showed satisfaction with both systems. However, less traction at the end of the residual limb was reported while looped liner was used.

CONCLUSION

The looped liner with hook fastener is safe and a good alternative for individuals with transtibial amputation as this system could solve some problems with the current systems. Clinical relevance The looped liner and hook fastener were shown to be good alternative suspension for people with lower limb amputation especially those who have difficulty to use and align the pin/lock systems. This system could safely tolerate centrifugal forces applied to the prosthesis during normal and fast walking.