RESEARCH ARTICLE


F.E.M. Stress-Investigation of Scolios Apex



A. Daghighi1, *, H. Tropp2, #, N. Dahlström3, A. Klarbring4
1 Department of Clinical and Experimental Medicine, Linköping University, 581 83 Linköping, Sweden
2 Department of Clinical and Experimental Medicine & Division of Surgery Orthopedics and Oncology, Linköping University, 581 83 Linköping, Sweden
3 Center for Medical Image Science and Visualization, Linköping University, 581 83 Linköping, Sweden
4 Department of Management and Engineering, Division of Solid Mechanics, Linköping University, 581 83 Linköping, Sweden


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Creative Commons License
© 2018 Daghighi et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


Note: The study was funded by the Swedish government in terms of ALF-grant (Event No:LIO-608221). All authors have contributed to all aspects of the work. The corresponding author (Daghighi) is in charge of the statistical analysis.* Address correspondence to this author at the Department of Clinical and Experimental Medicine, Linköping University, 581 83 Linköping, Sweden; E-mail: abtin.daghighi@liu.se# Research leader


Abstract

Background:

In scoliosis, kypholordos and wedge properties of the vertebrae should be involved in determining how stress is distributed in the vertebral column. The impact is logically expected to be maximal at the apex.

Aim:

To introduce an algorithm for constructing artificial geometric models of the vertebral column from DICOM stacks, with the ultimate aim to obtain a formalized way to create simplistic models, which enhance and focus on wedge properties and relative tilting.

Material/Methods:

Our procedure requires parameter extraction from DICOM image-stacks (with PACS,IDS-7), mechanical FEM-modelling (with Matlab and Comsol). As a test implementation, models were constructed for five patients with thoracal idiopathic scoliosis with varying apex rotation. For a selection of load states, we calculated a response variable which is based upon distortion energy.

Results:

For the test implementation, pairwise t-tests show that our response variable is non-trivial and that it is chiefly sensitive to the transversal stresses (transversal stresses where of main interest to us, as opposed to the case of additional shear stresses, due to the lack of explicit surrounding tissue and ligaments in our model). Also, a pairwise t-test did not show a difference (n = 25, p-value≈0.084) between the cases of isotropic and orthotropic material modeling.

Conclusion:

A step-by-step description is given for a procedure of constructing artificial geometric models from chest CT DICOM-stacks, such that the models are appropriate for semi-global stress-analysis, where the focus is on the wedge properties and relative tilting. The method is inappropriate for analyses where the local roughness and irregularities of surfaces are wanted features. A test application hints that one particular load state possibly has a high correlation to a certain response variable (based upon distortion energy distribution on a surface of the apex), however, the number of patients is too small to draw any statistical conclusions.

Keywords: Scoliosis, FEM Stress-Investigation, Thoracal Idiopathic, Pathological mechanisms, Mechanical loading, Comsol model.