Comparison of the mechanical properties of two designs of polyaxial pedicle screw

Abstract

Abstract In this study, the mechanical properties of a novel dual-core pedicle screw were compared with a commercially available cylindrical screw. In order to evaluate and compare their mechanical performance, a series of axial pullout, quasi-static and dynamic bend tests were conducted. In the pullout tests, three polyurethane (PU) foams (density: 0.16, 0.32 and 0.64 g/cm3) were used to compare the pullout strength between both screw types. The ultimate static strength of each screw was determined by a series of quasi-static cantilever bend tests. Dynamic tests were performed with a peak forces corresponding to 10%, 30%, 40%, 50%, 65% and 75% of the ultimate static strength of each screw type. Each specimen was subjected to a sinusoidally varying load which continued until the specimen fractured or reached 2.5 million cycles. The results of the pullout force indicated that the dual-core screws had higher pullout strength, in each PU foam, compared to cylindrical screws, however, the differences were not statistically significant. The average stiffness of dual-core screw during pullout from the 0.16 and 0.32 g/cm3 PU foams was significantly higher (p