Clinical Evaluation of the Access Socket Flexible Socket for Transtibial Prosthesis (AS-TT)

Transtibial amputation significantly impacts patient autonomy and quality of life, primarily due to the limitations of conventional rigid sockets, which restrict comfort and joint range of motion. The Access Socket (AS) is an innovative prosthetic socket combining a rigid carbon-fiber structure in key load-bearing areas with flexible urethane-resin (ProtheFLEX®) zones in regions typically rigid in conventional sockets. This hybrid design aims to improve comfort and pressure distribution while preserving the mechanical properties required for ambulation.

The AS has already demonstrated benefits in transfemoral amputees and is now reimbursed in France for that population. A preliminary uncontrolled study in 12 transtibial amputees suggested significant improvements in perceived function, comfort, satisfaction, and mobility.

This multicenter, randomized, open-label, two-arm crossover study aims to compare the (AS) with the standard rigid socket (RS) in 25 adults with transtibial amputation. Participants will wear each socket for approximately 4 weeks (after a 1-2 week adaptation period) in a randomized order. The primary outcome is the Patient Specific Functional Scale (PSFS). Secondary outcomes include comfort (SCS), satisfaction (OPUS), psychosocial adjustment (TAPES-R), mobility (PLUS-M), prosthesis utility (PEQ-U), and the proportion of patients electing to keep the AS at study completion.

Study Overview

• Status: Recruiting
• Conditions: Transtibial Amputation; Lower Limb Amputation Below Knee
• Intervention / Treatment: Device: Access Socket (AS); Device: Rigid Socket (RS)

Detailed Description

Background. Lower-limb amputation affects more than 7,500 people annually in France, with approximately 50% at the transtibial level. The socket is the critical interface between the residual limb and the prosthesis, transmitting mechanical forces while needing to remain comfortable. Currently, only RS (carbon or resin) are listed on the French reimbursable products list (LPPR) for transtibial amputation. Documented limitations of rigid sockets include restricted knee flexion, walking discomfort in challenging environments, donning difficulties, and suboptimal pressure distribution that does not adapt to residual-limb volume changes.

Investigational device. The AS follows the same molding and shaping principles as the standard RS but differs in two manufacturing steps: (1) carbon fibers are placed only on lateral, postero-inferior, and inferior areas to provide structural rigidity; (2) stratification uses urethane resin (ProtheFLEX®, already used in medical-device manufacturing) instead of epoxy or acrylic resin, creating soft zones in regions typically rigid in conventional sockets.

Comparator. Both sockets are manufactured from the same plaster mold to ensure strictly identical internal geometry. Only the material structure (carbon/urethane distribution) differs; all other prosthetic components (intermediate piece, prosthetic foot) are identical.

Design rationale. A double-blind design is not feasible because participants can perceive differences in socket rigidity and prosthesis weight. The crossover design controls for between-subject variability and order effects.

Sample size. Based on the preliminary study (Patient Specific Functional Scale (PSFS) standard deviation 1.74), to detect a difference of 1.3 points (the PSFS MDC₉₀ for 3 items) with 80% power and α=0.05, 19 participants are required. 25 will be enrolled to account for dropouts and to provide a more representative sample for secondary endpoints.

Visits. Four study visits over approximately 14-21 weeks per participant: inclusion (V0), evaluation after first socket period (V1), evaluation after second socket period (V2), and an optional follow-up visit (V3) one month later if the participant elects to keep the AS.

• Study Type: Interventional
• Enrollment (Estimated): 25
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Isabelle Loiret, MD; Phone Number: +33383529950; Email: isabelle.loiretpro@gmail.com
• Study Contact Backup: Name: Jonathan Pierret, PhD; Email: jonathan.pierret@ugecam.assurance-maladie.fr

Study Locations

• France
  • Clamart, France, 92140
    • Recruiting
    • Hôpital National d'Instruction des Armées (HNIA) Percy
    • Principal Investigator: Marie Thomas-Pohl, MD
    • Contact: Marie Thomas-Pohl, MD; Phone Number: +33 1.41.46.62.82; Email: marie.thomas@intradef.gouv.fr
  • Freyming-Merlebach, France, 57804
    • Recruiting
    • Hôpital Filieris de Freyming-Merlebach
    • Contact: Catherine Achour, MD; Phone Number: +33 3 83 52 98 61; Email: catherine.achour@filieris.fr
    • Principal Investigator: Catherine Achour
  • Grenoble, France, 38434
    • Recruiting
    • CHU Grenoble Alpes - Hôpital Sud
    • Contact: Solène Maret, MD; Phone Number: +33 4 76 76 60 25; Email: smaret2@chu-grenoble.fr
    • Principal Investigator: Solène MAret, MD
    • Sub-Investigator: Phillipe Escobar, MD
  • Nancy, France, 54000
    • Recruiting
    • Institut Régional de Médecine Physique et de Réadaptation (IRR) - Filière Locomoteur
    • Principal Investigator: Isabelle Loiret, MD
    • Contact: Jonathan Pierret, PhD; Email: jonathan.pierret@ugecam.assurance-maladie.fr
    • Contact: Christelle REQUENA; Phone Number: +33 3 83 52 98 61; Email: christelle.requena@ugecam.assurance-maladie.fr
  • Paris, France, 75007
    • Recruiting
    • Insititution Nationale des Invalides
    • Contact: Joseph Bascou, PhD; Phone Number: +33 3 87 51 30 30; Email: joseph.bascou@invalides.fr

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Unilateral or bilateral transtibial amputation
• Currently fitted with a definitive carbon rigid socket
• Any residual-limb shape
• Any etiology
• Able to understand simple instructions, read, write, and provide informed consent - or able to be accompanied by a trusted person in case of inability to read/write autonomously
• Provided free written informed consent
• Aged 18 years or older
• Affiliated to a social security system

Exclusion Criteria:

• Use of hydroalcoholic solution (HAS) for socket donning
• Currently fitted with a provisional socket
• Neurological pathology limiting capacity to participate in activities
• Orthopedic pathology limiting capacity to participate in activities
• Pregnant or breastfeeding women
• Minors
• Persons not under legal protection or unable to express consent
• Persons under guardianship or curatorship
• Persons under judicial protection

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Group 1 (RS -> AS); Participants wear their standard rigid socket (RS) for 4 weeks, complete evaluation, then switch to the Access Socket (AS) for 1-2 weeks of adaptation followed by 4 weeks of wear, with a second evaluation.	Device: Access Socket (AS); Hybrid prosthetic socket combining a rigid carbon-fiber structure in load-bearing areas (lateral, postero-inferior, inferior) with flexible urethane-resin (ProtheFLEX®) zones in regions typically rigid in conventional sockets. Manufactured from the same plaster mold as the rigid socket to ensure identical internal geometry.; Device: Rigid Socket (RS); Conventional definitive carbon-fiber rigid socket, currently the only socket type reimbursed in France for transtibial amputation (LPPR-listed). Standard of care comparator.
Active Comparator: Group 2 (AS -> RS); Participants receive the Access Socket (AS) first, with 1-2 weeks of adaptation followed by 4 weeks of wear and evaluation. They then switch to the standard rigid socket (RS) for 1-2 weeks of adaptation and 4 weeks of wear, with a second evaluation.	Device: Access Socket (AS); Hybrid prosthetic socket combining a rigid carbon-fiber structure in load-bearing areas (lateral, postero-inferior, inferior) with flexible urethane-resin (ProtheFLEX®) zones in regions typically rigid in conventional sockets. Manufactured from the same plaster mold as the rigid socket to ensure identical internal geometry.; Device: Rigid Socket (RS); Conventional definitive carbon-fiber rigid socket, currently the only socket type reimbursed in France for transtibial amputation (LPPR-listed). Standard of care comparator.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Patient Specific Functional Scale (PSFS) score	Patient-centered self-report tool. The patient identifies 3-5 specific activities they have difficulty performing, then rates their ability on a 0-10 scale (0 = unable to perform, 10 = able to perform at pre-injury level). The final score is the mean of the ratings	One time at the end of each 4-week wear period (V1, V2 and V3)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Socket Comfort Scale (SCS) score	0-10 numerical rating of socket comfort (0 = least comfortable imaginable, 10 = most comfortable imaginable)	One time at the end of each 4-week wear period (V1, V2 and V3)
Orthotics Prosthetics Users Survey (OPUS) score	Self-report instrument evaluating functional outcomes and quality of life specifically for orthosis and prosthesis users. Assesses lower-limb functional status, health-related quality of life, satisfaction with the device, and satisfaction with services. The higher the score, the more favorable the result for the device	One time at the end of each 4-week wear period (V1, V2 and V3)
Trinity Amputation and Prosthesis Experience Scale - Revised (TAPES-R) score	33-item multidimensional questionnaire evaluating psychosocial adjustment to amputation and prosthesis use, including general adjustment, social adjustment, activity restriction, and prosthesis satisfaction. The higher the global score, the more favorable the result for the device	One time at the end of each 4-week wear period (V1, V2 and V3)
Prosthesis Evaluation Questionnaire - Utility subscale (PEQ-U) score	The score is calculated as the mean of the 8 items in the subscale. Each item is rated on a Visual Analogue Scale (VAS) from 0 to 100. The total score ranges from 0 to 100, where higher scores indicate a better outcome (greater satisfaction and prosthesis utility)	One time at the end of each 4-week wear period (V1, V2 and V3)
Proportion of participants electing to keep the Access Socket at study completion	Percentage of participants who choose the AS over the RS at the end of the study, reported with 95% confidence interval. Participants are not informed of this option until the end of the study to avoid judgment bias	Through study completion, an average of 10 weeks

Collaborators and Investigators

• Sponsor: Union de Gestion des Etablissements des Caisses d'Assurance Maladie - Nord Est
• Collaborators: Otto Bock France SNC; Hôpital d'Instruction des armées Percy; Institution Nationale des Invalides; Clinical Investigation Center - University Hospital Grenoble; Hôpital Filieris de Freyming-Merlebach; Ortho Access; H20 Orthopedie
• Investigators: Principal Investigator: Isabelle Loiret, MD, Institut Régional de Médecine Physique et de Réadaptation (IRR), Nancy, France

Study record dates

Study Major Dates

• Study Start (Actual): April 27, 2026
• Primary Completion (Estimated): April 27, 2027
• Study Completion (Estimated): October 30, 2027

Study Registration Dates

• First Submitted: May 5, 2026
• First Submitted That Met QC Criteria: May 13, 2026
• First Posted (Actual): May 18, 2026

Study Record Updates

• Last Update Posted (Actual): May 18, 2026
• Last Update Submitted That Met QC Criteria: May 13, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: Rehabilitation; Quality of life; Comfort; cross over trial; Prosthetic socket; Transtibial prosthesis; Flexible socket; Access Socket; Patient Specific Scale
• Other Study ID Numbers: 2026-A00019-42

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: : Individual participant data will not be shared. Aggregated study results will be published in scientific journals and a summary report will be transmitted to the CPP within 12 months of study completion

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No