Abstract
INTRODUÇÃO: O sistema de fixação vertebral utilizando o parafuso pedicular é um dos métodos mais eficientes no tratamento de patologias da coluna vertebral. Quando o parafuso estiver submetido á força de arrancamento, este gera tensões ao seu redor, principalmente próximas do canal medular, situação esta que pode ser analisada pela técnica da fotoelasticidade. OBJETIVO: Foram analisadas as tensões internas geradas próximas ao canal medular de modelos fotoelásticos de vértebras utilizando diferentes medidas de parafusos do sistema de fixação vertebral submetidos à força de arrancamento. MÉTODO: Foi utilizado um modelo de vértebra lombar em material fotoelástico utilizando três medidas de parafusos pediculares (5, 6 e 7mm) do tipo USS1. As tensões internas ao redor do parafuso foram avaliadas em 12 pontos pré-determinados utilizando um polariscópio de transmissão plana. RESULTADOS: As regiões de maiores concentrações de tensões foram observadas entre o canal medular e as curvas do processo transverso. Nas comparações das médias das tensões cisalhantes máximas entre os parafusos 5 e 7, e 6 e 7 foram observadas diferenças estatísticas significativas e entre 5 e 6 não. CONCLUSÃO: Foi observada que as tensões internas são mais elevadas em áreas irregulares próxima ao canal medular, mostrando ser uma região crítica.
Highlights
The vertebrae fixation system using pedicular screws is one of the most efficient methods to treat vertebral spine pathologies
The objective of this study was to assess internal tensions generated near the medullar canal of vertebral photoelastic models using different screw sizes of a vertebral fixation system submitted to pullout strength
The regions with the highest tension concentrations were found between medullar canal and the transverse process curves, and on the medial surface of the distal portion of the screw
Summary
The vertebrae fixation system using pedicular screws is one of the most efficient methods to treat vertebral spine pathologies. The higher the number of visualized fringes, the higher the concentration of tension.[2] Those tensions may be similar to those found in the actual structure, since the material of the photoelastic model is homogenous and isotropic, and the model demands are similar to those seen in practice, not exceeding its elasticity limit.[1] In order to analyze tensions using the photoelastic technique, the following is required: Models prepared with photoelastic material and a transmission polaroscope This polaroscope is designed to polarize the light irradiated on the photoelastic model, as well as to analyze the light transmitted through that model.[3] The introduction of intrapedicular fixation by Roy-Camille et al.[4] in 1963 strongly leveraged the use of instrumentation through posterior approach with a pedicular screw, and this has been one of the most efficient methods of internal vertebral fixation in the treatment of several spinal conditions, such as vertebral fractures, scoliotic deformities, metastasis, and degenerative disorders.[5] One advantage is that the technique does not enter the neural canal, as occurs with other kinds of implants (hooks and sub-laminar wiring)[6], but, in cases where the screw is submitted to pullout strengths, this causes tension around it, and may lead to a critical situation, especially when near medullar canal. The objective of this study was to assess internal tensions generated near the medullar canal of vertebral photoelastic models using different screw sizes of a vertebral fixation system submitted to pullout strength
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