25/09/2008 - Biomechanical comparative study of compression strength between poliaxial and monoaxial screws

ABSTRACT
Objective: to compare rigidity of a pedicle fixation system composed of monoaxial pedicle screws to one composed of polyaxial screws, submitted to compression strengths. Methods: it has been used an experimental model to evaluate the fixation systems constructed and tested according to norms of 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 trials using fix screws; Group 2 used polyaxial screws. The metallic components implanted were produced with titanium coming from the same origin. The experimental groups were submitted to mechanical tests in a universal testing machine EMIC, model EMIC DL 1000. 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 1822.55 N. Results: the results obtained in the compression trial in the samples of Group 2 showed an average maximum charge of 967.17 N, and an average discharging load of 804.71 N. As the trials were in vitro, the results should be analyzed in the context that there are surgical characteristics of adaptation of the stalk/screw interface that are not reproducible in the surgical situation, when compared to tests carried out in ideal conditions. Conclusion: the system of fix screws has presented greater resistance to compression strengths as compared to the system with polyaxial screws.