Analysis of stress induced by screws in the vertebral fixation system.
OBJECTIVE
To compare, using photoelasticity, internal stress produced by USS II type screw with 5.2 and 6.2 mm external diameters, when submitted to three different pullout strengths.


METHODS
Two photoelastic models were especially made. The simulation was performed using loads of 1.8, 2.4 e 3.3 kgf.The fringe orders were evaluated around the screws. In all the models analyzed the shear stress were calculated.


RESULTS
Independently of the applied load, the smaller screw showed higher values of shear stress.


CONCLUSION
According to the analysis performed, we observed that the place of highest stress was in the first thread of the lead, close to the head of the screws. Experimental study.
['Fakhouri|Sarah Fakher|SF|', 'Shimano|Marcos Massao|MM|', 'de Araújo|Cleudmar Amaral|CA|', 'Defino|Helton Luiz Aparecido|HL|', 'Shimano|Antônio Carlos|AC|']
Biomechanics Elasticity Qualitative analysis Quantitative analysis Tensile strength