Clinical Evaluation of the Access Socket Flexible Socket for Transtibial Prosthesis

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.