Postfusion pullout strength comparison of a novel pedicle screw with classical pedicle screws on synthetic foams.

Pullout is a very common failure mode on the use of pedicle screws. Numerous studies were completed to increase the pullout strength of pedicle screws especially for osteoporotic bones. In this study, a previously designed pedicle screw type was tested before and after fusion condition. Synthetic polyurethane foams were used in all tests. Three different grades of foams were used in tests to simulate severely osteoporotic, osteoporotic, and healthy bones. Test blocks were produced and characterized in our clinical biomechanics laboratory. Foaming of polyurethane was accepted as fusion process (bone in growth). Pedicle screw including radial holes (new design) was tested both before and after the fusion. It also exhibited remarkably higher pullout strength after fusion than before fusion and most of other alternatives stated in the literature. In total, 70% higher pullout strength was achieved with new design after fusion. On the other hand, new design did not dominate other alternatives when comparison was carried out on severely osteoporotic and healthy bones. To the knowledge of the authors, this is the first study investigating the postfusion properties on synthetic foams.