Surrogate lower limb design for ankle-foot orthosis mechanical evaluation

Alexis Thibodeau; Patrick Dumond; Joongho Kim; Edward D Lemaire

doi:10.1177/20556683221139613

Surrogate lower limb design for ankle-foot orthosis mechanical evaluation

J Rehabil Assist Technol Eng. 2022 Nov 22:9:20556683221139613. doi: 10.1177/20556683221139613. eCollection 2022 Jan-Dec.

Authors

Alexis Thibodeau¹, Patrick Dumond¹, Joongho Kim¹, Edward D Lemaire^{1

2}

Affiliations

¹ Mechanical Engineering, University of Ottawa, Ottawa, ON, Canada.
² Ottawa Hospital Research Institute, Ottawa, ON, Canada.

Abstract

Purpose: This study designs and provides a pilot evaluation of a novel surrogate lower limb (SLL) that provides anatomically realistic three-dimensional (3D) foot motion, based on a literature consensus of passive lower limb motion. This SLL is intended to replace single axis surrogates currently used in mechanical testing of ankle-foot orthoses (AFO).

Material and methods: The SLL design is inspired by the Rizzoli foot model, with shank, hindfoot, midfoot, forefoot, and toe sections. Ball and socket joints were used between hindfoot-midfoot (HM)-forefoot sections. Forefoot-toes used a hinge joint. Three-dimensional printed nylon, thermoplastic polyurethane (TPU) and polylactic acid (PLA), as well as casted silicone rubber were used to re-create foot components. After fabrication, motion capture was performed to measure rotation using fiducial markers. The SLL was then loaded under both static and cyclic loads representing a 100 kg person walking for 500,000 cycles.

Results: Most joints were within 5° of target angles. The SLL survived static loads representing 1.5 times body weight for both static and cyclical loading.

Conclusions: This SLL moved as designed and survived testing loads, warranting further investigation towards enabling essential mechanical testing for AFO currently on the market, and helping to guide device prescription.

Keywords: ankle-foot orthosis; mechanical testing; range of motion; surrogate lower limb.