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A three-dimensional model to assess the effect of ankle joint axis misalignments in ankle-foot orthoses
Stefania Fatone1, William Brett Johnson2, Kerice Tucker2
1Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Prosthetics-Orthotics Center, Northwestern University, Chicago, IL, USA s-fatone@northwestern.edu.
Background:
Misalignment of an articulated ankle-foot orthosis joint axis with the anatomic joint axis may lead to discomfort, alterations in gait, and tissue damage. Theoretical, two-dimensional models describe the consequences of misalignments, but cannot capture the three-dimensional behavior of ankle-foot orthosis use.
Objectives:
The purpose of this project was to develop a model to describe the effects of ankle-foot orthosis ankle joint misalignment in three dimensions.
Study Design:
Computational simulation.
Methods:
Three-dimensional scans of a leg and ankle-foot orthosis were incorporated into a link segment model where the ankle-foot orthosis joint axis could be misaligned with the anatomic ankle joint axis. The leg/ankle-foot orthosis interface was modeled as a network of nodes connected by springs to estimate interface pressure. Motion between the leg and ankle-foot orthosis was calculated as the ankle joint moved through a gait cycle.
Results:
While the three-dimensional model corroborated predictions of the previously published two-dimensional model that misalignments in the anterior -posterior direction would result in greater relative motion compared to misalignments in the proximal -distal direction, it provided greater insight showing that misalignments have asymmetrical effects.
Conclusions:
The three-dimensional model has been incorporated into a freely available computer program to assist others in understanding the consequences of joint misalignments.
Clinical Relevance:
Models and simulations can be used to gain insight into functioning of systems of interest. We have developed a three-dimensional model to assess the effect of ankle joint axis misalignments in ankle-foot orthoses. The model has been incorporated into a freely available computer program to assist understanding of trainees and others interested in orthotics.
