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Proc Inst Mech Eng H. 2016 Feb;230(2):134-44. doi: 10.1177/0954411915621588. Epub 2015 Dec 15.

ISO 12189 standard for the preclinical evaluation of posterior spinal stabilization devices--II: A parametric comparative study.

Author information

1
Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering 'Giulio Natta', Politecnico di Milano, Milano, Italy IRCCS Istituto Ortopedico Galeazzi, Milano, Italy luigi.labarbera@polimi.it.
2
Department of Neurosurgery, Humanitas Clinical and Research Center, Milano, Italy.
3
Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering 'Giulio Natta', Politecnico di Milano, Milano, Italy IRCCS Istituto Ortopedico Galeazzi, Milano, Italy.

Abstract

The International Standardization Organization (ISO) 12189 standard was recently introduced to preclinically evaluate and compare the mechanical properties of posterior stabilization devices. This scenario presents some new significant steps ahead over the vertebrectomy model recommended by American Society for Testing and Materials (ASTM) F1717 standard: the modular anterior support allows for describing a closer scenario to the effective clinical use as well as to test very flexible and dynamic posterior stabilization devices. Despite these significant advantages, ISO 12189 received little attention in the literature. Anatomical parameters depending on the spinal level were compared to the published data or original measurements on biplanar stereoradiography on 13 patients. Other mechanical variables, describing the test set-up design, were considered and all parameters were investigated using a numerical parametric finite element model. Stress values were calculated by also considering their worst-case combination. The standard set-up represents quite well the anatomy of an instrumented average thoracolumbar segment. The parametric comparative analysis demonstrates a significant (even beyond +350%) maximum increase in the stress on the device, compared to the standard currently in use. The anterior support stiffness plays the most detrimental effect (maximum stress increases up to 396%). The initial precompression step has an important role in determining the final stress values achieved at peak load (up to +76%). Moreover, when combining these two contributions, an even higher stress increase may be achieved (up to 473%). Despite the other anatomical parameters playing a secondary role, their worst-case combination demonstrates that a device could potentially undergo higher stresses than those reached according to standard suggestions (maximum increase of 22.4% at L1). Any user/designer should be aware of these effects when using ISO 12189 standard for the preclinical evaluation of posterior spinal stabilization devices.

KEYWORDS:

ASTM F1717; ISO 10243; ISO 12189; fatigue; finite element; finite element model; parametric study; pedicle screw; preclinical evaluation; spine stabilization; standard

PMID:
26673809
DOI:
10.1177/0954411915621588
[Indexed for MEDLINE]

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