Acta Ortopédica Mexicana

Damián NZ, Reyes SA, Domínguez HVM, Urriolagoitia CG, Hernández GLH
A mechanical study of the spine internal fixator INO. First part: behavior under quasi-static flexion-compression load
Acta Ortop Mex 2000; 14 (1)

Language: Español
References: 8
Page: 9-15
PDF: 263.46 Kb.

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ABSTRACT

Mechanical evaluation in vitro of the INO (Instituto Nacional de Ortopedia) spinal fixation device employing pedicle screws and plates as longitudinal members was performed under an anterior compressive flexural cuasi-static load (n = 5), for determining its bending strength (N.m), stiffness (N.m/mm) and flexibility (mm/N.m). A total corpectomy defect was simulated using two plastic cylinders as vertebral bodies; the pedicle screws were attached to the plates with the nuts placed with their spherical side toward plates. The mechanical evaluation was performed utilizing an electromechanical Instron 4502 testing machine, and the load was applied with a lever arm distance of 39 mm. The average values obtained for the bending strength, stiffnes and flexibility are as follows: 31.184 N.m (sd = 2.73), 1.205 N.m/mm (sd = 0.225) and 0.852 mm/N.m (sd = 0.152) respectively; the failure observed was plastic elongation and bending of the four pedicle screws. The bending strength of the INO device represents the 309.5% and 53.7% of the bending strength of the Rogozinski and Isola devices, which are the ones with less and more bending strength respectively of the twelve spinal devices studied by Cunningham; mean while, its stiffness is the 41.9% and 17.5% of the stiffness of the Kirschner and Isola devices, the ones with less and more stiffness. Finally, the flexibillty of the INO device is the 238.6% and 572% of the flexibility of the Kirschner and Isola devices. Thereby, the INO spinal device has an acceptable bending strength but it is more flexible than all the spinal devices studied by Cunningham.


Key words: fixation, spine, biomechanic, analysis.


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