Transtibial Prosthetic Socket Strength: The Use of ISO 10328 in the Comparison of Standard and 3D-Printed Sockets

Abstract

Introduction Prosthetic sockets must withstand instances of maximum loading without failure. The goal of the present study is to evaluate the strength at failure and the failure mechanism for 3D-printed transtibial sockets, thermoplastic transtibial check sockets, and carbon-fiber definitive laminated transtibial sockets. Materials and Methods Three clinically available materials (carbon fiber, PETG thermoplastic, and 3D print polylactic acid [PLA]) were used to produce identically shaped sockets. In final assembly, the carbon-fiber sockets were designed for use both with and without a pin-lock system. Thermoplastic sockets and 3D-printed sockets were designed for use without a pin-lock system. These socket systems were then tested following International Standards Organization (ISO) 10328. Ultimate strength (US) at failure, maximum deflection at failure, and failure mechanism were determined. Results Both designs of carbon-fiber sockets had higher US values at failure than thermoplastic sockets and 3D-printed PLA sockets. Thermoplastic sockets had a slightly higher average US than 3D-printed sockets, but 3D-printed sockets exhibited a greater strength-to-weight ratio. Four distinct socket failure mechanisms were determined. Conclusions Failure mechanisms and US values differed for all socket types. Carbon-fiber sockets exhibited the highest US, but 3D-printed PLA sockets showed comparable strength to current thermoplastic sockets. Although the ISO 10328 testing standard was sufficient to complete these evaluations, the method lacked some socket-specific measures and loading conditions that could have improved comparisons between socket types.

3D printed transtibial prosthetic sockets: A systematic review

“…Five studies [ 21 , 28 – 31 ] used only 3D printing techniques for socket fabrication; five studies [ 6 , 24 – 27 ] used only traditional manufacturing techniques; and two studies [ 8 , 23 ] used both additives and traditional manufacturing techniques. Among the studies using 3D printing techniques, one study [ 28 ] used multiple manufacturing techniques, i.e., selective laser melting (SLM), selective laser sintering (SLS), and fused deposition modelling (FDM), and the other six studies [ 8 , 21 , 29 – 31 ] used only FDM.…”

“…Among the studies using 3D printing techniques, one study [ 28 ] used multiple manufacturing techniques, i.e., selective laser melting (SLM), selective laser sintering (SLS), and fused deposition modelling (FDM), and the other six studies [ 8 , 21 , 29 – 31 ] used only FDM. Among the traditional manufacturing techniques, seven studies [ 6 , 8 , 23 – 27 ] used lamination for definitive sockets.…”

“…For CF, the particles of carbon fiber in the final socket are not interwoven as they are in LCS reinforced with carbon fiber, hence they are not as strong. Three studies [ 8 , 23 , 31 ] used PLA, two studies [ 29 , 30 ] used PP, and two studies [ 21 , 28 ] used CF, while most LCS were made of carbon fiber and laminated with either nyglass or fiber glass [ 6 , 8 , 23 – 25 ].…”

“…For example, when performing testing at the P5-load level (used for assessing safety for a 100 kg patient), settling and proof tests occur at 920 N and 2013 N, respectively, and the socket is determined to pass the P5-level, i.e., is safe for use by a 100 kg patient, if the ultimate force surpasses 4025 N (twice the proof force) [ 20 ]. Condition I alignment was employed by 25% of studies [ 8 , 23 , 31 ] while 92% of studies performed testing under ISO Condition II [ 8 , 21 , 23 – 30 ]. Among all the studies, only one study used testing below the P5-level and tested one socket at each of the P3- and P4-levels.…”

“…Each relative orientation generated a different load line due to the different fixations of the ankle and knee joints as well as the length of the pylon. In this review, eight studies used the current alignment [ 8 , 21 , 23 – 26 , 28 , 31 ], two studies used the Neo alignment [ 27 , 30 ], and two studies used the Gerchutz alignment [ 6 , 29 ].…”