AccScience Publishing / IJB / Online First / DOI: 10.36922/ijb.3390

Tuning the mechanical responses of 3D-printed ankle-foot orthoses: A numerical study

Chenxi Peng1,2 Phuong Tran3 Simon Lalor4 Oren Tirosh5 Erich Rutz1,2,6,7,8,9*
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1 Department of Paediatrics, The University of Melbourne, Parkville, Victoria, Australia
2 Murdoch Children’s Research Institute, Parkville, Victoria, Australia
3 RMIT Centre for Additive Manufacturing, School of Engineering, RMIT University, Melbourne, Victoria, Australia
4 Orthotic and Prosthetic Department, The Royal Children’s Hospital Melbourne, Parkville, Victoria, Australia
5 School of Health and Biomedical Sciences, STEM College, RMIT University, Bundoora, Victoria, Australia
6 Bob Dickens Chair Paediatric Orthopaedic Surgery, The University of Melbourne, Parkville, Victoria, Australia
7 Orthopaedics Department, The Royal Children’s Hospital Melbourne, Parkville, Victoria, Australia
8 The Hugh Williamson Gait Analysis Laboratory, The Royal Children’s Hospital Melbourne, Parkville, Victoria, Australia
9 Medical Faculty, The University of Basel, Basel, Switzerland
IJB 2024, 10(3), 3390
Submitted: 9 April 2024 | Accepted: 8 May 2024 | Published: 7 June 2024
© 2024 by the 2024 Author(s). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution 4.0 International License ( )

Ankle-foot orthoses (AFOs) are frequently prescribed for children with cerebral palsy (CP) to correct specific features of abnormal gait. However, traditional AFO manufacturing and design involve labor-intensive processes and rely on subjective evaluations of clinicians. Recent advances in three-dimensional (3D) printing allow the rapid prototyping of AFOs, but the expanded design options complicate decision-making. This study aims to evaluate how AFO design affects the mechanical responses of 3D-printed AFOs. The lower limb geometry is established by a 3D-scanning system, and a prototypical AFO is designed, 3D printed, and tested under compression. A parametric study on the effect of base materials, thickness, and trimline location is conducted based on a validated numerical model. The results reveal that AFOs exhibit distinct behaviors under plantarflexion and dorsiflexion motions, with AFO stiffness correlating to thickness through a power function. AFO stiffness is more sensitive to posterior trim depth than inferior, while both trim depths significantly influence stress concentration around the ankle region. This investigation demonstrates the potential of combining 3D printing and computational modeling to improve the design and fabrication process of AFOs, providing insights into the development and customization of 3D-printed AFOs.

Cerebral Palsy
Ankle-foot orthoses
3D printing
Computational modeling
  1. Graham HK, Rosenbaum P, Paneth N, et al. Cerebral palsy. Nat Rev Dis Primers. 2016;2:15082. doi: 10.1038/nrdp.2015.82
  2. Ma N, Gould D, Camathias C, Graham K, Rutz E. Single-event multi-level surgery in cerebral palsy: a bibliometric analysis. Medicina. 2023;59(11). doi: 10.3390/medicina59111922
  3. Palmer FB, Shapiro BK, Wachtel RC, et al. The effects of physical therapy on cerebral palsy. A controlled trial in infants with spastic diplegia. N Engl J Med. 1988;318(13): 803-808. doi: 10.1056/NEJM198803313181302
  4. Rutz E, Hofmann E, Brunner R. Preoperative botulinum toxin test injections before muscle lengthening in cerebral palsy. J Orthop Sci. 2010;15(5):647-653. doi: 10.1007/s00776-010-1509-6
  5. De Pieri E, Romkes J, Wyss C, et al. Effect of botulinum toxin A on muscle function in patients with cerebral palsy and its relation to gait. Gait Posture. 2020;81:74-76. doi: 10.1016/j.gaitpost.2020.07.062
  6. Lintanf M, Bourseul JS, Houx L, Lempereur M, Brochard S, Pons C. Effect of ankle-foot orthoses on gait, balance and gross motor function in children with cerebral palsy: a systematic review and meta-analysis. Clin Rehabil. 2018;32(9):1175-1188. doi: 10.1177/0269215518771824
  7. Chisholm AE, Perry SD. Ankle-foot orthotic management in neuromuscular disorders: recommendations for future research. Disabil Rehabil Assist Technol. 2012;7(6):437-449. doi: 10.3109/17483107.2012.680940
  8. Schröder J-H, Barandun GA, Leimer P, Morand R, Göpfert B, Rutz E. Novel modular walking orthosis (MOWA) for powerful correction of gait deviations in subjects with a neurological disease. Children. 2024;11(1). doi: 10.3390/children11010030
  9. Ridgewell E, Dobson F, Bach T, Baker R. A systematic review to determine best practice reporting guidelines for AFO interventions in studies involving children with cerebral palsy. Prosthet Orthot Int. 2010;34(2):129-145. doi: 10.3109/03093641003674288
  10. Mason RDF, Vuletich W. Ankle-foot orthosis. Google Patents; 1981.
  11. Zhou C, Yang Z, Li K, Ye X. Research and development of ankle-foot orthoses: a review. Sensors. 2022;22(17). doi: 10.3390/s22176596
  12. Wickramasinghe S, Do T, Tran P. FDM-based 3D printing of polymer and associated composite: a review on mechanical properties, defects and treatments. Polymers. 2020;12(7). doi: 10.3390/polym12071529
  13. Silva R, Veloso A, Alves N, Fernandes C, Morouco P. A review of additive manufacturing studies for producing customized ankle-foot orthoses. Bioengineering (Basel). 2022;9(6). doi: 10.3390/bioengineering9060249
  14. Wojciechowski E, Chang AY, Balassone D, et al. Feasibility of designing, manufacturing and delivering 3D printed ankle-foot orthoses: a systematic review. J Foot Ankle Res. 2019;12(1):11. doi: 10.1186/s13047-019-0321-6
  15. Chen RK, Chen L, Tai BL, Wang Y, Shih AJ, Wensman J. Additive manufacturing of personalized ankle-foot orthosis. In: Proceedings of Transactions of the North American Manufacturing Research Institution of SME (NAMRC42); 2014:42.
  16. Cha YH, Lee KH, Ryu HJ, et al. Ankle-foot orthosis made by 3D printing technique and automated design software. Appl Bionics Biomech. 2017;2017:9610468. doi: 10.1155/2017/9610468
  17. Wojciechowski EA, Cheng TL, Hogan SM, et al. Replicating and redesigning ankle-foot orthoses with 3D printing for children with Charcot-Marie-Tooth disease. Gait Posture. 2022;96:73-80. doi: 10.1016/j.gaitpost.2022.05.006 
  18. Kumar R, Kumar R, Kalra P, et al. Effectiveness of 3D printed carbon fiber composite strut in customized ankle foot orthosis. Compos Struct. 2023;324:117540. doi: 10.1016/j.compstruct.2023.117540
  19. Teng PSP, Leong KF, Kong PW, et al. A methodology to design and fabricate a smart brace using low-cost additive manufacturing. Virtual Phys Prototyp. 2022;17(4):932-947. doi: 10.1080/17452759.2022.2090384
  20. Liu Z, Zhang P, Yan M, Xie YM, Huang GZ. Additive manufacturing of specific ankle-foot orthoses for persons after stroke: a preliminary study based on gait analysis data. Math Biosci Eng. 2019;16(6):8134-8143. doi: 10.3934/mbe.2019410
  21. Ranz EC, Russell Esposito E, Wilken JM, Neptune RR. The influence of passive-dynamic ankle-foot orthosis bending axis location on gait performance in individuals with lower-limb impairments. Clin Biomech (Bristol, Avon). 2016;37: 13-21. doi: 10.1016/j.clinbiomech.2016.05.001
  22. Vasiliauskaite E, Ielapi A, De Beule M, et al. A study on the efficacy of AFO stiffness prescriptions. Disabil Rehabil Assist Technol. 2021;16(1):27-39. doi: 10.1080/17483107.2019.1629114
  23. Mavroidis C, Ranky RG, Sivak ML, et al. Patient specific ankle-foot orthoses using rapid prototyping. J Neuroeng Rehabil. 2011;8(1):1. doi: 10.1186/1743-0003-8-1
  24. Totah D, Menon M, Jones-Hershinow C, Barton K, Gates DH. The impact of ankle-foot orthosis stiffness on gait: a systematic literature review. Gait Posture. 2019;69: 101-111. doi: 10.1016/j.gaitpost.2019.01.020
  25. Kerkum YL, Buizer AI, van den Noort JC, Becher JG, Harlaar J, Brehm MA. The effects of varying ankle foot orthosis stiffness on gait in children with spastic cerebral palsy who walk with excessive knee flexion. PLoS One. 2015;10(11):e0142878. doi: 10.1371/journal.pone.0142878
  26. Aboutorabi A, Arazpour M, Ahmadi Bani M, Saeedi H, Head JS. Efficacy of ankle foot orthoses types on walking in children with cerebral palsy: a systematic review. Ann Phys Rehabil Med. 2017;60(6):393-402. doi: 10.1016/
  27. Sumiya T, Suzuki Y, Kasahara T. Stiffness control in posterior-type plastic ankle-foot orthoses: effect of ankle trimline. Part 2: orthosis characteristics and orthosis/patient matching. Prosthet Orthot Int. 1996;20(2):132-137. doi: 10.3109/03093649609164431
  28. Bielby SA, Warrick TJ, Benson D, et al. Trimline severity significantly affects rotational stiffness of ankle-foot orthosis. J Prosthet Orthot. 2010;22(4):204-210. doi: 10.1097/JPO.0b013e3181f9082e
  29. Shuman BR, Totah D, Gates DH, Gao F, Ries AJ, Russell Esposito E. Comparison of five different methodologies for evaluating ankle-foot orthosis stiffness. J Neuroeng Rehabil. 2023;20(1):11. doi: 10.1186/s12984-023-01126-7
  30. Ielapi A, Forward M, De Beule M. Computational and experimental evaluation of the mechanical properties of ankle foot orthoses: a literature review. Prosthet Orthot Int. 2019;43(3):339-348. doi: 10.1177/0309364618824452
  31. Bregman DJ, Rozumalski A, Koops D, de Groot V, Schwartz M, Harlaar J. A new method for evaluating ankle foot orthosis characteristics: BRUCE. Gait Posture. 2009;30(2):144-149. doi: 10.1016/j.gaitpost.2009.05.012
  32. Shuman BR, Russell Esposito E. Multiplanar stiffness of commercial carbon composite ankle-foot orthoses. J Biomech Eng. 2022;144(1). doi: 10.1115/1.4051845
  33. Totah D, Menon M, Gates DH, Barton K. Design and evaluation of the SMApp: a stiffness measurement apparatus for ankle–foot orthoses. Mechatronics. 2021;77. doi: 10.1016/j.mechatronics.2021.102572
  34. Zou D, He T, Dailey M, et al. Experimental and computational analysis of composite ankle-foot orthosis. J Rehabil Res Dev. 2014;51(10):1525-1536. doi: 10.1682/JRRD.2014-02-0046 
  35. Stier B, Simon JW, Reese S. Numerical and experimental investigation of the structural behavior of a carbon fiber reinforced ankle-foot orthosis. Med Eng Phys. 2015;37(5):505-511. doi: 10.1016/j.medengphy.2015.02.002
  36. Schrank ES, Hitch L, Wallace K, Moore R, Stanhope SJ. Assessment of a virtual functional prototyping process for the rapid manufacture of passive-dynamic ankle-foot orthoses. J Biomech Eng. 2013;135(10):101011-101017. doi: 10.1115/1.4024825
  37. Syngellakis S, Arnold MA, Rassoulian H. Assessment of the non-linear behaviour of plastic ankle foot orthoses by the finite element method. Proc Inst Mech Eng H. 2000;214(5):527-539. doi: 10.1243/0954411001535561
  38. Ielapi A, Lammens N, Van Paepegem W, et al. A validated computational framework to evaluate the stiffness of 3D printed ankle foot orthoses. Comput Methods Biomech Biomed Engin. 2019;22(8):880-887. doi: 10.1080/10255842.2019.1601712
  39. Abdalsadah FH, Hasan F, Murtaza Q, Khan AA. Design and manufacture of a custom ankle–foot orthoses using traditional manufacturing and fused deposition modeling. Prog Addit Manuf. 2021;6(3):555-570. doi: 10.1007/s40964-021-00178-2
  40. Sumihira W, Otani T, Kobayashi Y, Tanaka M. Computational modelling of ankle-foot orthosis to evaluate spatially asymmetric structural stiffness: importance of geometric nonlinearity. Proc Inst Mech Eng H. 2022;236(9):1357-1364. doi: 10.1177/09544119221114199
  41. Eddison N, Mulholland M, Chockalingam N. Do research papers provide enough information on design and material used in ankle foot orthoses for children with cerebral palsy? A systematic review. J Child Orthop. 2017;11(4): 263-271. doi: 10.1302/1863-2548.11.160256
  42. ASTM International. Standard Test Method for Tensile Properties of Plastics. West Conshohocken, PA: ASTM International; 2014. doi: 10.1520/D0638-14
  43. Wickramasinghe S, Peng C, Ladani R, Tran P. Analysing fracture properties of bio-inspired 3D printed suture structures. Thin Wall Struct. 2022;176:109317. doi: 10.1016/j.tws.2022.109317
Conflict of interest
The authors declare no conflicts of interest.
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International Journal of Bioprinting, Electronic ISSN: 2424-8002 Print ISSN: 2424-7723, Published by AccScience Publishing