Northwestern University Flexible Subischial Vacuum Socket for persons with transfemoral amputation: Part 2 Description and Preliminary evaluation

Quantitative analysis of interface pressures in transfemoral prosthetic sockets

BACKGROUND

Among the different factors affecting socket comfort, the pressure applied on residual limb tissues is a crucial parameter for the success or failure of any prosthetic device. However, only a few incomplete data are available on people with transfemoral amputation, in this regard. This work aims at filling this gap in the literature.

METHODS

Ten people with transfemoral amputation wearing 3 different socket designs were recruited in this study: 2 ischial containment sockets featured by proximal trim lines that contain the ischial tuberosity and ramus and greater trochanter, 2 subischial sockets with proximal trim lines under the ischium level, and 6 quadrilateral sockets with proximal trim lines that contain the greater trochanter and create a horizontal seat for the ischial tuberosity. The pressure values at the anterior, lateral, posterior, and medial areas of the socket interface were recorded during 5 locomotion tasks (ie, horizontal, ascent, and descent walking, upstairs and downstairs) by using an F-Socket System (Tekscan Inc., Boston, MA). Gait segmentation was performed by exploiting plantar pressure, which was acquired by an additional sensor under the foot. Mean and standard deviation of minimum and maximum values were calculated for each interface area, locomotion task, and socket design. The mean pressure patterns during different locomotion tasks were reported, as well.

RESULTS

Considering all subjects irrespective of socket design, the mean pressure range resulted 45.3 (posterior)-106.7 (posterior) kPa in horizontal walking; 48.3 (posterior)-113.8 (posterior) kPa in ascent walking; 50.8 (posterior)-105.7 (posterior) kPa in descent walking; 47.9 (posterior)-102.9 (lateral) kPa during upstairs; and 41.8 (posterior)-84.5 (anterior) kPa during downstairs. Qualitative differences in socket designs have been found.

CONCLUSIONS

These data allow for a comprehensive analysis of pressures acting at the tissue-socket interface in people with transfemoral amputation, thus offering essential information for the design of novel solutions or to improve existing ones, in this field.

Design trends in actuated lower-limb prosthetic systems: a narrative review

INTRODUCTION

Actuated lower limb prostheses, including powered (active) and semi-active (quasi-passive) joints, are endowed with controllable power and/or impedance, which can be advantageous to limb impairment individuals by improving locomotion mechanics and reducing the overall metabolic cost of ambulation. However, an increasing number of commercial and research-focused options have made navigating this field a daunting task for users, researchers, clinicians, and professionals.

AREAS COVERED

The present paper provides an overview of the latest trends and developments in the field of actuated lower-limb prostheses and corresponding technologies. Following a gentle summary of essential gait features, we introduce and compare various actuated prosthetic solutions in academia and the market designed to provide assistance at different levels of impairments. Correspondingly, we offer insights into the latest developments of sockets and suspension systems, before finally discussing the established and emerging trends in surgical approaches aimed at improving prosthetic experience through enhanced physical and neural interfaces.

EXPERT OPINION

The ongoing challenges and future research opportunities in the field are summarized for exploring potential avenues for development of next generation of actuated lower limb prostheses. In our opinions, a closer multidisciplinary integration can be found in the field of actuated lower-limb prostheses in the future.

A finite element analysis of load distribution during donning and orthostatic posture in the ITOP hybrid subischial socket

INTRODUCTION

Pressure and shear stresses applied to the stump of a transfemoral amputee wearing a newly designed prosthetic socket have been analyzed by a finite element modeling approach.

METHODS

The new socket was developed by the Istituto Tecnico Ortopedico Preneste, and it was named the "hybrid subischial socket." This work aimed at understanding the loads' distribution on the stump surface in 2 operative conditions: at the end of the wearing phase and during the orthostatic posture. The model of the stump was composed of 4 different materials: the femoral bone, the muscle tissue, the fat, and the skin layers. Except for the bone (rigid), the biological tissues were modeled as Neo-Hookean, and their mechanical properties were taken from the literature. The socket was composed of a containment frame, made of carbon fiber composite material, a shell made of flexible silicone, and a liner made of hyperelastic silicone.

RESULTS

The results of our simulation show that the main support areas are located in a proper position, in agreement with the ideal principles of this prosthetic design, and the maximum pressures are well below the pain threshold reported in the literature for the same contact areas.

CONCLUSIONS

We can conclude that although the upper rim of the socket is well below the ischiatic area, the new socket design allows for a safe and comfortable support of the body weight. This is in agreement with the evidence of a good functionality and acceptance of this prosthetics gathered in the many real applications.

A prospective assessment of an adjustable, immediate fit, subischial transfemoral prosthesis

Objective

To assess the feasibility of an adjustable, subischial transfemoral prosthesis by comparing self-reported outcome measures regarding socket comfort, fit and utility relative to a persons’ conventionally made socket. Assessing limb compressibility was another aim of this study.

Design

A single-group pre-post intervention design.

Setting

Physical medicine and rehabilitation biomechanics laboratory.

Participants

All 18 enrolled participants (N = 18) completed the feasibility trial. There were 16 men and 2 women with an average age of 59.4 (±7) years. Most of the participants (61.1%) had worn a socket for 1 to 10 years before the trial, 22.2% of the participants had worn one for less than a year, and 16.7% of the participants had worn a prosthesis for more than 10 years.

Intervention

Participants were fit with the study prosthesis and used it for a 2-week home trial.

Main Outcome Measures

A Prosthetic Comfort and Utility Questionnaire was completed on the participant's conventional prosthetic device and the subischial socket system after the trial.

Results

The adjustable subischial prostheses were rated superior overall to the participant's conventional sockets (40.9 ± 7.2 vs 32.8 ± 10.8; P=.004). Six of the 10 parameters measured (adjustability, overall fit, prosthesis weight, sitting comfort, standing comfort, and standing stability) were rated higher for the adjustable prostheses compared to the conventional sockets. Compression of the soft tissues of the thigh ranged from 5.6 ± 4.2 cm at the distal end to 7.3 ± 3.6 cm at the proximal site. There were no falls, skin breakdown, or limb ischemia. At the 2-month telephone follow-up, 61% of subjects had transitioned to using the adjustable subischial socket most of the time.

Conclusions

The adjustable, immediate fit, subischial prosthesis provided safe, comfortable, and functional ambulation for persons with transfemoral limb loss in this short-term feasibility study. This study supports the consideration of a new paradigm in transfemoral prosthetics—adjustable subischial sockets. These devices should be tested in a larger multi-center study.

The Impact of Limited Prosthetic Socket Documentation: A Researcher Perspective

The majority of limb prostheses are socket mounted. For these devices, the socket is essential for adequate prosthetic suspension, comfort, and control. The socket is unique among prosthetic components as it is not usually mass-produced and must instead be custom-made for individual residual limbs by a prosthetist. The knowledge of what constitutes "good" socket fit is gained by expert prosthetists and technicians over years of experience, and rarely documented. The reliance on tacit knowledge makes it difficult to standardize the criteria for a well-fitting socket, leading to difficulties understanding the impact of socket fit. Despite its importance, the workflow for socket fitting is often overlooked in literature. Due to the customized nature of sockets, if information is provided in literature, generally only the type of socket and suspension mechanism is noted, with information regarding the fitting and manufacturing processes omitted. In this article, the concerns, issues and consequences arising from lack of upper and lower limb socket documentation are discussed from a researcher perspective, supported by healthcare professionals and socket fabrication specialists. Key changes are proposed to the way socket manufacturing and evaluation are documented to assist future research.

Prosthesis satisfaction and quality of life in US service members with combat-related major lower-limb amputation

BACKGROUND

Military amputee patient care programs offer extensive services, including advanced prosthetic devices, to restore function and improve quality of life (QOL) among veterans and service members with combat-related limb loss, but research on satisfaction with these devices is limited.

OBJECTIVE

To assess prosthesis satisfaction and QOL in US service members and veterans with combat-related major lower-limb amputation.

STUDY DESIGN

Cross-sectional study.

METHODS

Eighty-six participants with combat-related major lower-limb amputation completed the Orthotics and Prosthetics Users' Survey (OPUS) Satisfaction with Device scale and Quality of Well-Being Scale, Self-Administered, for the Wounded Warrior Recovery Project.

RESULTS

Most participants (62%-88%) responded Agree or Strongly Agree to OPUS Satisfaction with Device items on the fit, weight, comfort, ease of donning, appearance, and durability of their prosthesis. By contrast, the majority of participants (55%-79%) responded Disagree or Strongly Disagree to items on clothes being free of wear and tear, skin free of abrasions and irritations, and the affordability of their prosthesis. In linear regression analysis, total OPUS Satisfaction with Device score was positively associated with Quality of Well-Being Scale, Self-Administered score (β = 0.0058; P = 0.004).

CONCLUSIONS

Findings indicate the majority of participants were satisfied with the overall functionality of their prosthesis, but dissatisfied with the effect of their prosthesis on clothing and skin, as well as expenses related to their prosthesis. Additionally, prosthesis satisfaction was positively associated with QOL.

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.

The Hybrid Subischial Socket for Persons With Transfemoral Amputation: Gait Parameters and Clinical Assessment of a Case Series

BACKGROUND

The subischial socket interface design is a promising new shape of socket for persons with transfemoral amputation. Typically, the proximal trim line is located distal to the ischial tuberosity, improving comfort in prosthetic users without interfering with gait parameters compared to Ischial Containment Socket (ICS). No studies have investigated the performances of a subischial sockets with suction suspension system. A new subischial socket (Hybrid Subischial Socket - HySS) combined with a hypobaric passive suspension system has been recently developed.

OBJECTIVE

To assess the effects of HySS in terms of comfort, hip range-of-motion and gait parameters.

METHODOLOGY

Three persons with transfemoral amputation were tested first using their usual ICS and then after one month of continuous use of HySS.

FINDINGS

The following parameters improved in all participants using HySS: 1) hip range-of-motion, 2) walking speed and distance, 3) Timed-Up-and-Go-Test time, 4) stride length, 5) double support duration, 6) peak value of hip extension during stance, 7) satisfaction with the prosthesis.

CONCLUSION

These findings suggest that the use of HySS could allow improvements for prosthetic use.

Comparison of Ischial Containment and Subischial Sockets on Comfort, Function, Quality of Life, and Satisfaction With Device in Persons With Unilateral Transfemoral Amputation: A Randomized Crossover Trial

OBJECTIVE

To compare comfort and functional performance of the Northwestern University Flexible Subischial Vacuum (NU-FlexSIV) Socket with the ischial containment (IC) socket in persons with unilateral transfemoral amputation.

DESIGN

Randomized crossover trial with two 7-week periods.

SETTING

Private prosthetic clinics and university research laboratory.

PARTICIPANTS

A total of 30 enrolled (N=30); 25 participants completed the study with full (n=18) or partial data (n=7).

INTERVENTIONS

Two custom-fabricated sockets (IC and NU-FlexSIV), worn full-time for 7 weeks, with testing at 1, 4, and 7 weeks after socket delivery.

MAIN OUTCOME MEASURES

The primary outcome was change in Socket Comfort Score (SCS) at 7 weeks. Secondary outcomes at 7 weeks included the Orthotic and Prosthetic Users' Survey (OPUS) to assess lower extremity functional status, health-related quality of life, and satisfaction with device, as well as the 5-Times Rapid Sit-to-Stand Test, Four Square Step Test, and T-Test of Agility to assess functional performance.

RESULTS

At 7 weeks, the mean SCS for IC (7.0±1.7) and NU-FlexSIV (8.4±1.1) Sockets were significantly different (P<.001; 95% confidence interval, 0.8-2.3). Results from a linear mixed-effects model, accounting for data from all time points, indicated that the SCS was 1.7 (SE=0.45) points higher for the NU-FlexSIV Socket (P<.001). For the secondary outcomes, only OPUS satisfaction with device was significantly better in the NU-FlexSIV Socket after accounting for all data points.

CONCLUSIONS

The results suggest that after 7 weeks' accommodation, the NU-FlexSIV Socket was more comfortable and led to greater satisfaction with device than the IC socket in persons with unilateral transfemoral amputation and K3/K4 mobility. Other patient-reported outcomes and function were no different between sockets.

Clinical Outcome of Transfemoral Direct Socket Interface (Part 2)

BACKGROUND

Amputation at the transfemoral (TF) level reduces the rate of successful prosthetic fitting, functional outcome, and quality of life (QoL) compared with transtibial amputation. The TF socket interface is considered the most critical part of the prosthesis, but socket discomfort is still the most common user complaint. Direct Socket for transfemoral prosthesis users is a novel interface fabrication process where the socket is shaped and laminated directly on the residual limb and delivered in a single visit.

OBJECTIVES

The aim of this study was to investigate if prosthetic users' quality of life (QoL), comfort, and mobility with a Direct Socket TF interface were comparable to their experience with their previous prostheses.

METHODOLOGY

The pre/post design prospective cohort study included 47 subjects. From this cohort, 36 subjects completed the 6-months follow-up (mean age 58 years, 27 males). Outcomes at baseline included EQ-5D-5L®, PLUS-M™, CLASS, ABC, AMPPRO, and TUG. At 6-weeks and 6-months, subjects repeated all measures. Seven Certified Prosthetist (CP) investigators performed observations and data collection at six different sites (from July 2018 to April 2020).

FINDINGS

Results showed significant improvement in all outcome measures for the 36 subjects that completed both 6-weeks and 6-months follow-ups. CLASS sub-scales showed significantly improved stability, suspension, comfort, and socket appearance. Improvement in K-Level and less use of assistive devices were observed with the AMPPRO instrument, indicating improved user mobility and performance. QoL was also increased, as measured in Quality-Adjusted-Life-Years (QALY) from the EQ-5D-5L.

CONCLUSIONS

Evidence from the findings demonstrate that the Direct Socket TF system and procedure can be a good alternative to the traditional method of prosthetic interface delivery.

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.

Transfemoral Socket Fabrication Method Using Direct Casting: Outcomes Regarding Patient Satisfaction with Device and Services

BACKGROUND

Direct Socket for transfemoral (DS-TF) prosthetic user is a novel method of fabricating a laminated interface on to the residual limb but requires different training, production method and service model than what most prosthetists are familiar with. This method and model may improve patient satisfaction by enabling interface fabrication and delivery in one visit.

OBJECTIVES

Document patient satisfaction regarding DS-TF interface versus the prosthetic users' previous socket in terms of interface function and the clinic service model.

METHODOLOGY

In this longitudinal study (from July 2018 to April 2020), the DS-TF was implemented in six prosthetic clinics across the United States. Certified prosthetists (CP) and assistants were trained using a standard protocol. 47 prosthetic users participated, both those in need of a new socket and those without need. Two modules from the Orthotics and Prosthetics Users' Survey (OPUS), involving questions related to satisfaction with the Device and Services, was used to evaluate each DS-TF user outcome vs. baseline. The only part of the prosthesis that was replaced was the interface, except in 2 cases.

FINDINGS

Each DS-TF interface was fabricated, fit and delivered in a single clinic visit. At 6-months follow-up, 38 users reported an average of 29.8% increase in satisfaction with their new interface compared with original, and a 14.8% increase in satisfaction with the services they received from the clinic in providing of the new prosthesis vs. their original prosthesis. The main outcome increases were between baseline (initial fitting) and 6-week follow-up and remained consistent after 6 months. This improvement was consistent irrespective if the user needed a new socket for clinical reasons or not.

CONCLUSIONS

This study shows that after a standardized training and implementation, the DS-TF fabrication process including a new interface, improves the user's satisfaction with their prosthetic device and services.

The effect of the transfemoral prosthetic socket interface designs on skeletal motion and socket comfort: A randomized clinical trial

BACKGROUND

The most crucial aspect of a prosthesis is the socket, as it will directly determine gait stability and quality. The current standard of care ischial ramus containment socket is reported to increase coronal stability through gait; however, socket discomfort is the primary complaint among prosthetic users.

OBJECTIVES

The purpose of this study is to compare ischial ramus containment to alternatives in the transfemoral amputee population. All subjects were fit with three different sockets: traditional ischial ramus containment, a dynamic socket, and a sub-ischial. In this study, authors hypothesized socket skeletal motion would be equivalent across interventions.

STUDY DESIGN

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

METHODS

Outcome measures were socket comfort score and skeletal motion, viewed coronally with X-ray measuring the position of the skeleton in relationship to the socket in full weight-bearing and full un-loading.

RESULTS

The mean age was 38.2 and mean Amputee Mobility Predictor score was 40. Mean vertical movement, horizontal movement, single limb prosthetic stance, mean femoral adduction in swing and stance, and median socket comfort score were not statistically different.

CONCLUSION

The socket design did not significantly effect skeletal motion and socket comfort. All socket designs are suitable depending on the patient-centric preferences and prosthetist skill set.

CLINICAL RELEVANCE

The comfort of the standard of care transfemoral amputation socket has been widely reported as problematic. A comparison of alternative designs in a controlled clinical trial environment will assist the clinician in understanding the impact of design regarding skeletal motion and comfort. Users could benefit from alternatives applied in clinical practice.

Parametric Design and Hybrid Fabrication of Above-Knee Prosthesis

BACKGROUND

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.

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSION

The proposed approach can be adapted for mass customization, required to meet the large gap in demand and supply, especially in resource-constrained settings.

Technique modifications for a suction suspension version of the Northwestern University Flexible Sub-Ischial Vacuum socket: The Northwestern University Flexible Sub-Ischial Suction socket

BACKGROUND AND AIM:

Development of a passive suction version of the Northwestern University Flexible Sub-Ischial Vacuum socket would expand application of sub-ischial sockets to a larger proportion of persons with transfemoral amputation. While active vacuum suspension provides more positive coupling of the residual limb to the prosthetic socket, there are circumstances when use of active vacuum is not appropriate or feasible. Therefore, this technical note describes the technique modifications required to cast, fabricate, and fit a passive suction version of the Northwestern University Flexible Sub-Ischial Vacuum socket (i.e. the Northwestern University Flexible Sub-Ischial Suction socket).

TECHNIQUE:

Most technique modifications stem from the use of an internal seal with the Northwestern University Flexible Sub-Ischial Suction socket and the need to account for the greater relative motion occurring between the residual limb and socket with passive suction compared to active vacuum suspension.

DISCUSSION:

Between January 2015 and March 2018, 266 Northwestern University Flexible Sub-Ischial Suction sockets were fit successfully using the described technique modifications.

CLINICAL RELEVANCE

A passive suction version of the Northwestern University Flexible Sub-Ischial Vacuum socket-the Northwestern University Flexible Sub-Ischial Suction socket-broadens the application of sub-ischial sockets to a larger proportion of the population with transfemoral amputation.

Change in residual limb size over time in the NU-FlexSIV socket: A case study

BACKGROUND:

This case study represented a unique opportunity wherein a long-time user of sub-ischial sockets had kept nearly every socket he wore for a decade. This individual let us borrow these sockets so we could digitize them and indirectly assess change in residual limb size over time by calculating changes in socket volume and circumferences over time.

CASE DESCRIPTION AND METHODS:

Over a decade, the subject maintained a relatively stable body weight of 84-88 kg and received nine sub-ischial sockets. The internal surface of each socket was scanned using a mechanical digitizer and volume and circumferences calculated.

FINDINGS AND OUTCOMES:

Socket volume increased 31.3%, from a low of 2659.2 cm³ for the oldest socket to a high of 3490.6 cm³ for the most recent socket. Proximal circumferences increased more than distal circumferences with a 15.9% total increase proximally versus 8.9% total increase distally.

DISCUSSION AND CONCLUSION:

The results suggest that this individual's residual limb increased in size over time despite the compressive effect of the socket and liner. In addition, the increase in circumference was greater proximally than distally, which is where the remaining muscle bellies are located.

CLINICAL RELEVANCE

This case study provides insight into the long-term effect of the sub-ischial socket on residual limb volume given compression of the soft tissues by the socket system.

Test-Retest Reliability of Dynamic Balance Performance-Based Measures Among Adults With a Unilateral Lower-Limb Amputation

BACKGROUND

There is large variation in administration of performance-based, dynamic balance measures among adults with lower-limb amputation (LLA). Further, there has been limited exploration of test-retest reliability of these measures in adults with lower-limb loss, including whether there is a difference in reliability if one records "best" vs "average" performance across trials.

OBJECTIVE

To determine test-retest reliability of several balance tests for both "best" and "average" score performance in community-dwelling adults with a unilateral LLA, including quantification of the precision of individual scores (SE of the measurement, SEM) and estimates of minimal detectable change (MDC₉₀ ).

DESIGN

Cross-sectional study.

SETTING

Mobile research laboratory.

PARTICIPANTS

27 participants (55.5% female) with an average age of 51 (SD = 12.2) years, who were predominantly community-ambulators (92.5%), after a unilateral transtibial (n = 20), transfemoral (n = 5), or other major lower-extremity (n = 2) amputation, were included. Median time since amputation was 6.3 (2.3, 19 [25th, 75th interquartile range]) years.

METHODS

Reliability was evaluated using intraclass correlation coefficient (ICC) models (3,1 or 3,k). SEMs and MDC₉₀ values with 95% confidence intervals (CIs) were calculated.

MAIN OUTCOME MEASURES

360^o Turn Test, 5 Times Sit-To-Stand, Functional Reach Test, Figure-of-8 Walk Test, and Four Square Step Test (FSST).

RESULTS

The ICCs (3,1 or 3,k) for all tests (for both "best" and "average" performance) were considered good-to-excellent and CIs varied from 0.69 (95% CI = 0.40-0.85) to 0.97 (95% CI = 0.95-0.99). For most tests, "best" and "average" performance demonstrated similar ICC values. MDC₉₀ values did not surpass 10% of test means for any of the measures.

CONCLUSIONS

The dynamic balance measures evaluated for use among community-dwelling adults with a unilateral LLA demonstrated excellent reliability, along with high precision of scores and MDC values that did not exceed 10% of testing means. Either best or average scoring may be used when administering the majority of these tests, as long as the assessment method is appropriately documented and replicated at follow-up to allow direct comparisons. With the FSST, clinicians should consider taking the average of two FSST trials.

LEVEL OF EVIDENCE

III.

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.

Northwestern University Flexible Subischial Vacuum Socket for persons with transfemoral amputation-Part 1: Description of technique

BACKGROUND

Current transfemoral prosthetic sockets restrict function, lack comfort, and cause residual limb problems. Lower proximal trim lines are an appealing way to address this problem. Development of a more comfortable and possibly functional subischial socket may contribute to improving quality of life of persons with transfemoral amputation.

OBJECTIVES

The purpose of this study was to (1) describe the design and fabrication of a new subischial socket and (2) describe efforts to teach this technique.

STUDY DESIGN

Development project.

METHODS

Socket development involved defining the following: subject and liner selection, residual limb evaluation, casting, positive mold rectification, check socket fitting, definitive socket fabrication, and troubleshooting of socket fit. Three hands-on workshops to teach the socket were piloted and attended by 30 certified prosthetists and their patient models.

RESULTS

Patient models responded positively to the comfort, range of motion, and stability of the new socket while prosthetists described the technique as "straight forward, reproducible."

CONCLUSION

To our knowledge, this is the first attempt to create a teachable subischial socket, and while it appears promising, more definitive evaluation is needed. Clinical relevance We developed the Northwestern University Flexible Subischial Vacuum (NU-FlexSIV) Socket as a more comfortable alternative to current transfemoral sockets and demonstrated that it could be taught successfully to prosthetists.