OBJECTIVE: to compare the rigidity of a pedicle fixation system composed of fixed pedicle screws with double locked system (internal and external) to one composed of fixed pedicle screws with single internal locked system, submitted to compression strengths. METHODS: the experimental model used to evaluate the fixation systems was constructed according to the standard described by the American Society for Testing Materials (ASTM) in trial F1717-04. The samples were divided into two groups. Group 1 was composed of tests with fixed screws with double locked system; in Group 2 fixed screws with single internal locked system were used. Three sets of rods and screws were used for each group; these sets were submitted to a biomechanical test. The metallic components were produced by the same company and with the same origin. The experimental groups were submitted to mechanical tests at the universal testing machine EMIC, model EMIC DL 10000. RESULTS: the results obtained in the compression trial in samples of Group 1 showed an average maximum charge of 2104,15 N and an average discharging load of 1882,55 N. The results obtained in the compression trial in the samples of Group 2 showed an average maximum charge of 1420,5 N and an average discharging load of 1314,37 N. CONCLUSION: the screws with double locked system (Group 1) presented greater resistance to compression strengths when compared to the screws with single internal locked system.
Bone screws; Bone plates; Fracture fixation; internal
