Clinical Evaluation of the Access Socket Flexible Socket for Transtibial Prosthesis

Overview

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.

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.

Interventions

• 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.

Primary outcome measures

• Patient Specific Functional Scale (PSFS) score [Time frame: One time at the end of each 4-week wear period (V1, V2 and V3)]

Secondary outcome measures (5)

• Socket Comfort Scale (SCS) score [Time frame: One time at the end of each 4-week wear period (V1, V2 and V3)]
• Orthotics Prosthetics Users Survey (OPUS) score [Time frame: 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 [Time frame: One time at the end of each 4-week wear period (V1, V2 and V3)]
• Prosthesis Evaluation Questionnaire - Utility subscale (PEQ-U) score [Time frame: 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 [Time frame: Through study completion, an average of 10 weeks]

Eligibility criteria

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

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: No

Study design

Allocation

Randomized

Model

Crossover

Masking

Open label

Primary purpose

Treatment

Study locations

France · 5 centers

• Hôpital National d'Instruction des Armées (HNIA) Percy — Clamart
• Hôpital Filieris de Freyming-Merlebach — Freyming-Merlebach
• CHU Grenoble Alpes - Hôpital Sud — Grenoble
• Institut Régional de Médecine Physique et de Réadaptation (IRR) - Filière Locomoteur — Nancy
• Insititution Nationale des Invalides — Paris

Identifiers

NCT: NCT07592325 · 2026-A00019-42

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗