Research Papers

Assessment of Mechanical Characteristics of Ankle-Foot Orthoses

[+] Author and Article Information
Amanda Wach

Department of Biomedical Engineering,
Marquette University,
Olin Engineering Center,
Room 206, 1515 W. Wisconsin Avenue,
Milwaukee, WI 53233
e-mail: awach10@gmail.com

Linda McGrady, Mei Wang

Department of Orthopaedic Surgery,
Medical College of Wisconsin,
Milwaukee, WI 53226

Barbara Silver-Thorn

Department of Biomedical Engineering,
Marquette University,
Milwaukee, WI 53233

Manuscript received July 7, 2017; final manuscript received March 5, 2018; published online April 30, 2018. Assoc. Editor: Brian D. Stemper.

J Biomech Eng 140(7), 071007 (Apr 30, 2018) (6 pages) Paper No: BIO-17-1296; doi: 10.1115/1.4039816 History: Received July 07, 2017; Revised March 05, 2018

Recent designs of ankle-foot orthoses (AFOs) have been influenced by the increasing demand for higher function from active individuals. The biomechanical function of the individual and device is dependent upon the underlying mechanical characteristics of the AFO. Prior mechanical testing of AFOs has primarily focused on rotational stiffness to provide insight into expected functional outcomes; mechanical characteristics pertaining to energy storage and release have not yet been investigated. A pseudostatic bench testing method is introduced to characterize compressive stiffness, device deflection, and motion of solid-ankle, anterior floor reaction, posterior leaf spring, and the intrepid dynamic exoskeletal orthosis (IDEO) AFOs. Each of these four AFOs, donned over a surrogate limb, were compressively loaded at different joint angles to simulate the foot-shank orientation during various subphases of stance. In addition to force–displacement measurements, deflection of each AFO strut and rotation of proximal and supramalleolar segments were analyzed. Although similar compressive stiffness values were observed for AFOs designed to reduce ankle motion, the corresponding strut deflection profile differed based on the respective fabrication material. For example, strut deflection of carbon-fiber AFOs resembled column buckling. Expanded clinical test protocols to include quantification of AFO deflection and rotation during subject use may provide additional insight into design and material effects on performance and functional outcomes, such as energy storage and release.

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Grahic Jump Location
Fig. 1

Study AFOs: (a) solid-ankle AFO, (b) anterior floor reaction AFO, (c) PhatBrace AFO, and (d) IDEO

Grahic Jump Location
Fig. 2

Mechanical testing setup for (a) phase 1: strut deflection with posterior strut markers and (b) phase 2: AFO proximal and supramalleolar regional motion assessment with active markers (white). These two test configurations also illustrate the adjustable loading plate to simulate the different limb orientations corresponding to the various stance subphases.

Grahic Jump Location
Fig. 3

Mean (and SD) compressive stiffness of tested AFOs during latter subphases of stance (top) across the latter five loading cycles. The corresponding regressed force–displacement curves used to determine stiffness for the IDEO are also shown (bottom).

Grahic Jump Location
Fig. 4

Displacement of posterior strut markers in the sagittal plane during strut deflection testing. The strut marker positions during preload (midstance: circles; terminal stance: diamonds; preswing: squares) are shown in the inset figures; the strut displacement at the (reduced—see Table 2) target load for various subphases of stance is shown for each AFO.



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