title: Analysis of stress induced by screws in the vertebral fixation system.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Universidade de São Paulo, Faculdade de Medicina de Ribeirão Preto, Ribeirão Preto, SP, Brazil, Department de Biomechanics, Medicine and Rehabilitation of the Locomotor System, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil.
authors.forename: Sarah Fakher
authors.initials: SF
authors.lastname: Fakhouri
authors.affiliation: Universidade Federal do Triângulo Mineiro, Departement of Mechanical Engineering, Uberaba, MG, Brazil, Departement of Mechanical Engineering, Universidade Federal do Triângulo Mineiro, Uberaba, MG, Brazil.
authors.forename: Marcos Massao
authors.initials: MM
authors.lastname: Shimano
authors.affiliation: Universidade Federal de Uberlândia, Faculdade de Engenharia Mecânica, Department of Mechanical Projects, Uberlândia, MG, Brazil, Department of Mechanical Projects, Faculdade de Engenharia Mecânica, Universidade Federal de Uberlândia, Uberlândia, MG, Brazil.
authors.forename: Cleudmar Amaral
authors.initials: CA
authors.lastname: de Araújo
authors.affiliation: Universidade de São Paulo, Faculdade de Medicina de Ribeirão Preto, Ribeirão Preto, SP, Brazil, Department de Biomechanics, Medicine and Rehabilitation of the Locomotor System, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil.
authors.forename: Helton Luiz Aparecido
authors.initials: HL
authors.lastname: Defino
authors.affiliation: Universidade de São Paulo, Faculdade de Medicina de Ribeirão Preto, Ribeirão Preto, SP, Brazil, Department de Biomechanics, Medicine and Rehabilitation of the Locomotor System, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil.
authors.forename: Antônio Carlos
authors.initials: AC
authors.lastname: Shimano
keywords: Biomechanics; Elasticity; Qualitative analysis; Quantitative analysis; Tensile strength