Prosthetics: Lower Limb – Sockets 2 (4.4.1.a-e)

Prosthetic sockets are a key component in connecting the user’s body with the prosthesis [1]. The socket fit is critical for enabling prosthesis users to effectively complete activities of daily living. Normal fluctuations in residual limb volume often affect the fit between the residual limb and the prosthetic socket [2]. Vacuum-assisted socket suspension (VASS) technology, also known as elevated vacuum, is a form of socket suspension commonly used by prosthesis users to maintain this fit [3].

The purpose of this study was to conduct a systematic review to evaluate the current body of evidence on elevated vacuum functional impacts and proven clinical benefits.

Database searches were conducted to locate published evidence regarding VASS: MEDLINE via PubMed, Scopus, Cumulative Index to Nursing and Allied Health Literature (CINAHL), and Web of Science. Keywords and subject headings (when available) for elevated vacuum and persons with limb loss were utilized to identify literature addressing vacuum-assisted socket system technology in prosthesis users. Resulting references were screened in two stages: (1) eliminate duplicates and (2) determine articles that met inclusion/exclusion criteria. Two raters independently completed stage 2 screening to verify inclusion/exclusion and for classification as Pertinent, Not Pertinent, or Uncertain. Discrepancies on any article classifications were resolved by discussion between the two raters.

The search yielded 2,366 manuscripts. Stage 1 screening identified and removed 632 duplicate records. The remaining 1,734 records were reviewed in Stage 2 screening. Stage 2 screening eliminated an additional 1,670 articles, resulting in 64 articles meeting eligibility criteria. An additional 2 eligible studies familiar to the team were subsequently added, resulting in 66 articles included in this review. Data in each article were extracted for categorization and analysis. The studies also underwent examination for quality of research. The complete results of the systematic review will be presented.

The systematic review presents the latest evidence regarding VASS technology and its impact on prosthesis user function. VASS research has indicated benefits for prosthetic socket fit, residual limb volume management, and outcomes as compared to other suspension systems. The evidence collected in the systematic review serves as the foundation for clinical practice guidelines and evidence tables to support clinical care.

1. Klute GK. J Rehabil Res Dev. 2009;46(3):293-304.
2. Goswami J. Prosthet Orthot Int. 2003;27(2):107-113.
3. Rink C. J Rehabil Res Dev. 2016;53(6):1121-1132.

The work was supported by an AOPA Research Award administered by the Center for Orthotic and Prosthetic Learning.

Sub-ischial sockets have been suggested as a more comfortable alternative to Ischial Containment (IC) Sockets for people with transfemoral amputation due to the lower proximal trim lines [1-4]. However, it is unclear if removing the ischial containment might reduce function due to compromised coronal plane stability or improve function due to increased hip range of motion.

To compare comfort and functional performance of the Northwestern University Flexible Sub-Ischial Vacuum (NU-FlexSIV) Socket to the IC Socket in persons with unilateral transfemoral amputation.

Two custom sockets (IC; NU-FlexSIV) worn in random-order full-time for 7 weeks.. Testing at 1, 4 and 7 weeks. Primary outcome: change in Socket Comfort Score (SCS) at 7 weeks. Secondary outcomes: Orthotic and Prosthetic Users’ Survey (OPUS) to assess lower-extremity functional status, health-related quality-of-life, and satisfaction with device, also 3D-gait analysis at multiple speeds, 5-Times Rapid Sit-to-Stand Test, Four Square Step Test, and T-Test of Agility to assess functional performance. Gait variables related to hip motion and coronal plane stability assessed. Two analysis approaches used: paired t-tests at week 7 and linear mixed-effect models (LMM, main and interaction effects of socket and time considered using data from all weeks).

30 participants enrolled, 25 completed with full (n=18) or partial data (n=7). 19/25 males, mean age: 45.9±13.7years, mean height: 177.2±11.6cm, and mean mass: 88.6±19.7kg. 23/25 had amputation due to non-vascular issues. All had K3/K4 mobility levels. At 7 weeks (n=19), mean SCS for IC (7.0±1.7) and NU-FlexSIV (8.4±1.1) were significantly different (p<0.001, 95%CI = 0.8, 2.3). Similarly, LMMs (n=25) indicated SCS was 1.7 (SE=0.45) points higher for NU-FlexSIV (p<0.001). Among other outcomes, only OPUS satisfaction was significantly better in NU-FlexSIV using LMM (n=25). No differences at 7 weeks in gait variables between sockets at normal speed (n=19). However, using LMMs (n=25) there was a significant main effect of socket: prosthetic-side sagittal plane hip motion significantly greater for NU-FlexSIV at all speeds. No differences in lateral trunk flexion or step width for any speed for either analysis.

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 non-vascular unilateral transfemoral amputation and K3/K4 mobility. Other patient-reported outcomes and function were no different between sockets. The NU-FlexSIV Socket did not alter gait biomechanics related to hip motion and coronal plane socket stability.

1. Fatone S, Caldwell R. Prosthet Orthot Int. 2017; 41: 237-45. 2. Fatone S, Caldwell R. Prosthet Orthot Int 2017; 41: 246-50. 3. Kahle et al. Prosthet Orthot Int. 2020; 44: 145-54. 4. Kahle JT, Highsmith MJ. Gait Posture. 2014; 40: 315-20.

Work supported by Assistant Secretary of Defense for Health Affairs through the Peer Reviewed Orthopaedic Research Program (Award No. W81XWH-15-1-0708).

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.

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

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.  

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. 

OPUS CSD questions related to the function of the interface for all subjects indicate a significant improvement in user satisfaction with their DS-TF interface over their previous interface. All improvements were consistent between the 6-week and 6-month study periods. At 6MFU the average CSS score was 93, or 14.8% higher, a significant improvement. 

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

Paternò L, et al. Sockets for limb prostheses: A review of existing technologies and open challenges. IEEE Trans Biomed Eng. 2018;65(9):1996–2010. 

Kamrad I, et al. SwedeAmp-the Swedish amputation and prosthetics registry: 8-year data on 5762 patients with lower limb amputation... Acta Orthop. 2020;22:1-7.

Study financially supported by Össur, authors are employees of Össur except I. Atlason. Principle Investigators received no compensation from Össur.

The prosthetic socket is the interface which connects the human body to the artificial limb and allows transmission of body weight and forces during gait.

The review purpose is to assess the quality of scientific evidence and compare this for a variety of available TF socket designs. Comparisons will be made of socket biomechanics, metabolic efficiency and comfort and the advantages/disadvantages associated with each design.

Socket designs included were: Quadrilateral; Ischial Containment; Marlo Anatomical Socket; Sub-Ischial; High-Fidelity and the Socket-less socket. A literature review was conducted in five online databases - Compendex, Embase, PubMed, ProQuest Materials science and ProQuest Biological Science - using Boolean search terms and truncation of relevant keywords. Included articles were published between 1989 and 2018. A predetermined methodological criterion was used in conjunction with a modified version of the Oxford Levels of Evidence to assess and grade the quality of selected articles.

13 clinical studies were included in this review. Based on the chosen search strategy and quality criterion, this review found a limited, low quality evidence base for all included socket designs. All articles, except one, compared the various socket designs: Quad; Quad and MAS; MAS; Sub-Ischial and HiFi, against an IC socket as this was deemed the ‘standard of care’ design.

Although Ischial Containment attained the highest volume of evidence, this socket design was not proven to be superior. The variety of biomechanical features pertaining to each socket design provide several advantages/disadvantages. Recommendations are made for future research.

I would like to thank Marlo Ortiz, R.J. Garrick, Randall Alley and Jay Martin for the images and additional information they provided regarding socket designs.

Nearly 40% of individuals with lower limb amputation report that their biggest concern when receiving a prosthesis is comfort and fit [1].  One major contributor to socket discomfort is residual limb volume fluctuations throughout the day. Adjustable-volume sockets, utilize a dynamic mechanism to allow the user to modify the socket volume to manage fit and comfort. There is limited evidence on the efficacy of adjustable sockets, however.

The purpose of this study was to explore clinician perceptions and experiences fitting adjustable-volume prosthetic sockets.

An anonymous online survey was developed and pilot tested with local prosthetists.  The survey contained questions about prosthetists’ demographics, whether they had previously fit an adjustable socket, whether these fittings were successful, and what challenges they experienced. The survey was distributed to certified prosthetists through advertisements at a national prosthetics conference and through oandp-l.  We compared demographics between the groups who had and who had not fit adjustable-volume prosthetic sockets using Fisher’s exact tests.

A total of 221 prosthetists responded to the survey. After screening, 195 responses were deemed eligible. A majority of the respondents had fit an adjustable socket (82.1%). There were no differences in prosthetist characteristics between those who had and had not fit an adjustable socket (p > 0.081).  Respondents had fit a variety of adjustable sockets, with various degrees of perceived success (Fig 1). For successful fits, the most often reported challenges experienced were increased bulk (n=181), complicated fabrication (n = 141) and poor cosmesis (n =127).  The most common reasons prosthetists had not fit an adjustable socket were lack of training (n = 15) and not believing they were effective (n = 12). However, 81.8% respondents would fit an adjustable socket if the obstacles they indicated were removed.

A majority of the prosthetists surveyed were aware of adjustable prosthetic sockets and had fit them in their clinical practice. Prosthetists reported improved outcomes with more customizable designs.  Adjustable socket technology may have several benefits, but prior to widespread use, prosthetists need guidance on proper candidate selection, best practice fitting and fabrication procedures, and clear evidence of functional advantages of these systems over traditional socket styles.

1. Seaman, J.P. J Prosthet Orthot, 22, 257-65, 2010.

This work was supported by the U.S. Department of Defense under Award No. W81XWH-18-1-0656