A methodology for the customization of hinged ankle-foot orthoses based on in vivo helical axis calculation with 3D printed rigid shells

Abstract

This study aims to develop techniques for ankle joint kinematics analysis using motion capture based on stereophotogrammetry. The scope is to design marker attachments on the skin for a most reliable identification of the instantaneous helical axis, to be targeted for the fabrication of customized hinged ankle-foot orthoses. These attachments should limit the effects of the experimental artifacts, in particular the soft-tissue motion artifact, which affect largely the accuracy of any in vivo ankle kinematics analysis. Motion analyses were carried out on two healthy subjects wearing customized rigid shells that were designed through 3D scans of the subjects’ lower limbs and fabricated by additive manufacturing. Starting from stereophotogrammetry data collected during walking and dorsi-plantarflexion motor tasks, the instantaneous and mean helical axes of ankle joint were calculated. The customized shells matched accurately the anatomy of the subjects and allowed for the definition of rigid marker clusters that improved the accuracy of in vivo kinematic analyses. The proposed methodology was able to differentiate between subjects and between the motor tasks analyzed. The observed position and dispersion of the axes were consistent with those reported in the literature. This methodology represents an effective tool for supporting the customization of hinged ankle-foot orthoses or other devices interacting with human joints functionality.

Biomechanics in AIMETA

“…Since the 60 s of the last century, but especially in the last twenty years there has been a remarkable development of exoskeletons, more of lower-limb devices than of the upper-limb ones since the former are easier to design and control. In [30] techniques are proposed for the ankle motion analysis and the more precise definition of the instantaneous axis of motion, based on stereophotogrammetry and markers properly attached to the skin that limit the effect of the skin artifact. The proposed methodology showed to be an effective tool to customize hinged ankle foot orthoses and other devices interacting with the human joint functionality.…”

Comparison between Helical Axis and SARA Approaches for the Estimation of Functional Joint Axes on Multi-Body Modeling Data

“…Medial and lateral positions refer to a right lower limb. The markers' positioning followed a similar configuration used by the authors in a previous study, in which rigid plastic shells were used to limit rigid and non-rigid cluster deformation during in vivo analyses [19]. Among each marker cluster, one of the markers was placed out of the plane includin the other three markers to account for any variability in marker positioning that normal occurs during experimentation.…”

“…The algorithm for IHA estimation used is based on the original work of Woltring et al [23], and it has been already outlined in previous works from the authors [10,19]. It considers a screw-like helical motion assumption.…”

“…These errors indirectly affect the estimation of joint centers and axes that are necessary for the related kinematic and dynamic analyses [15,16]. For this reason, several techniques proposed in the literature have tried to tackle those issues, which are certainly evident during in vivo analyses [17][18][19].…”