Structural evaluation of lower-limb prosthetic sockets for running– Part 1: design, implementation and first assessment of an innovative test bench

• This study describes an innovative testing method that is specific for sockets for running applications, and represents a novelty in the Prosthetic Community, as no evidence exists about structural testing of sport-specific sockets. • Running sockets must sustain very demanding loads, and the lack of knowledge about their mechanical properties can put athletes at risk and hinders the development in materials and fabrication technologies. • Our test method was designed and applied using data from in-vivo acquisition of elite Paralympic gold medalists. This study reports the design, implementation and initial evaluation of a test bench for the structural characterization of lower-limb prosthetic sockets for sprinting prostheses. Similarly to ISO 10328, the test method subjects a socket to combined loading conditions by applying a single test force through prescribed lever arms, which are set by two-way perpendicular sliding guides. Loading conditions and lever arms were calculated based on the kinematics and kinetics of two elite Paralympic athletes – one with transfemoral and one with transtibial amputation - running at 7.0 m/s and 9.5 m/s respectively, using force plates and optoelectronic cameras installed on an indoor track, and assessing the external bending moments acting at their socket-adapter interface. Two critical loading conditions were identified for the transfemoral socket, at 35% (Condition I, 24743 Nmm sagittal and 24244 Nmm frontal plane moments) and 72% (Condition II, 36279 Nmm sagittal and -14477 Nmm frontal plane moments) of the stance phase. A single critical condition was identified for the transtibial socket, at 51% of the stance phase, largely dominated by a 206388 Nmm sagittal plane moment. The test system was assessed on two transfemoral and one transtibial sprinting sockets from the two athletes, resulting in an ultimate load at failure of 8240 N (Condition I) and 6056 N (Condition II) for the transfemoral socket, and of 7904 N for the transtibial socket. The test bench proved to be a versatile tool for reproducing in-vivo conditions and could be valuable to support calculation-based sport socket design and cyclic testing.