A finite element analysis of a T12 vertebra in two consecutive examinations to evaluate the progress of osteoporosis

Provatidis, C.; Vossou, C.; Petropoulou, E.; Balanika, A.; Lyritis, G.

doi:10.1016/j.medengphy.2008.12.003

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Volume 31, Issue 6 , Pages 632-641, July 2009

A finite element analysis of a T12 vertebra in two consecutive examinations to evaluate the progress of osteoporosis

C. Provatidis
- School of Mechanical Engineering, National Technical University of Athens, Zografos Campus, 9 Heroes of Polytechnion Ave., GR-15780 Athens, Greece
- Corresponding author. Tel.: +30 210 7721520; fax: +30 210 7722347.
C. Vossou
- School of Mechanical Engineering, National Technical University of Athens, Zografos Campus, 9 Heroes of Polytechnion Ave., GR-15780 Athens, Greece
E. Petropoulou
- School of Mechanical Engineering, National Technical University of Athens, Zografos Campus, 9 Heroes of Polytechnion Ave., GR-15780 Athens, Greece
A. Balanika
- 2nd Radiology Department, University of Athens, University General Hospital “Attikon”, Athens, Greece
G. Lyritis
- LRMS, “Th. Garofalidis,” KAT Hospital, University of Athens, Athens, Greece

Received 20 February 2008; received in revised form 17 December 2008; accepted 21 December 2008. published online 02 February 2009.

Abstract

Osteoporosis is a metabolic disease that causes bones to become fragile and be more likely to break. As basic clinical examinations to detect osteoporosis, dual energy X-ray absorptiometry (DXA) and quantitative computer tomography (QCT) are used. In the framework of a typical clinical examination, QCT scans were obtained from the T12 vertebra of an elderly woman and osteoporosis was diagnosed. One year later, new QCT scans were obtained in order to evaluate her clinical condition. Using both sets as primary information, two patient-specific finite element (FE) models were created and analyzed under compressive load. Vertebral bone was treated as orthotropic material and its elastic modulus was set as an indirect function of Hounsfield Units (HU). Commercial software for medical image processing and FE analysis, along with in house codes, were used for the mechanical analysis of the FE models. Alterations in the geometry/shape of the vertebra as well as in the distributions of several mechanical quantities were detected between the two FE models.

As far as the volume of the vertebra is concerned, it augmented by a percentage of 9.7% while the volume of the vertebral body alone increased by 5.6%. In all the maximum values of the mechanical quantities a measurable reduction was observed (axial compressive displacement: 37.9%, von Mises stress: 23.8%, von Mises strains: 15.1%) and all the investigated distributions in the second FE model became smoother. Finally, the percentage of volume with von Mises strains greater than 4500μstrain dropped from 8.9%, in the first examination, to 4.9% in the second one. Clinically, the prescribed medication seems to have reinforced the structural stability of the vertebra as a whole and through external remodeling the shape of the vertebra changed in a way that the majority of its volume was relieved from stresses and strains of high magnitude.