Stresses distributions of screws of the vertebral fixation systems submitted to pullout strength using plane transmission photoelasticity. / Distribuição de tensões de parafusos do sistema de fixação vertebral submetidos a arrancamento utilizando fotoelasticidade de transmissão plana

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The treatment of spinal deformities, degenerative disease, injuries and tumors on the vertebral column often demand the accomplishment of the internal fixation. The pedicular screws arising enabled the accomplishment of column segmental instrumentation more stable and became a standard procedure in accomplishing surgeries of correction, deformities stabilization and column instability in thoracic, lumbar and sacral pathologies. The best vertebral segment for the screw implantation is the lumbar area due to a larger diameter of the pedicles. The photoelasticity has been used in scientific studies in order to determine the stress/strain distribution in structural systems, because it allows a qualitative and quantitative analysis of the state of stress, through the observation of optical effects. In this work was used this technique to determine and analyze the internal stress of the photoelastic models under the influence of pedicular screws type USS1 submitted to pullout strength. In order to accomplish the photoelastic analysis 12 models divided in 3 groups were made. Each of them contained 4 photoelastic models. The first group, G1, was composed by the screw of 5 mm of external diameter, the second, G2, was composed by the screw of 6 mm external diameter and the third, G3, by a screw of 7 mm external diameter. The simulation was performed using loads of 0.75 Kgf and 1.5 Kgf. The fringe orders were evaluated around the screws using the Tardy compensation method. In all the models analyzed were calculated the shear stress. The results showed that using the load of 0.75 Kgf the shear stress in the 5 mm screw was bigger than in the 6 mm screw, which was bigger than in the 7mm screw. With a load of 1.5 Kgf there was equality among the three external diameter screws and comparing these two last loads, the last result prevailed. According to the analysis realized in the 12 models, we observed that the place of highest stress is at the peak of the crests mainly at the tips of the screws. Concluding, this technique is efficient enough because through the quantitative and qualitative analysis it was possible to compare the vertebral fixation screws, verifying witch one is more susceptible to pullout.

ASSUNTO(S)

pedicular screw fotoelasticidade parafuso pedicular pullout strength biomecânica. força de arrancamento photoelasticity biomechanics.

ACESSO AO ARTIGO

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