Screw-bone finite element models for screw pullout simulation

Objective To establish screw-bone finite element (FE) models for screw pullout simulation.Methods A pedicle screw model with a diameter of 6.5 mm,a model of screw-low density porous foam and a model of screw-high density porous foam were established and validated against the published data.Next,a screw-bone model was established and imported into the ANSYS software for FE simulation to study the dynamic bone responses during screw pullout according to the criteria set by American Association for Testing Materials (ASTM).A velocity loading of 0.01 mm/s with a maximum displacement of 2.7 mm was applied on the screw.For validation,the screw-foam models with 2 different densities were used for comparison of the pullout forces with the experimental data published.Results In validation,the predicted pullout forces were 2028.8 N in the high density foam model and 607.0 N in the low density foam model,respectively.They were in good agreement with the data of Hashemi et al.(2132.5 ± 119.3 N and 688.2 ±91.4 N,respectively).The load-displacement curves in the FE models were similar to the published (1.8 mm versus 1.5mm).In the simulation of screw pullout,the areas around the crew changed in volume in the process of pullout.Conclusion The dynamic screw-bone FE model established and validated by the present study can be used in simulation of pullout of pedicle screws to study mechanical bone responses to the pullout. Key words: Osteoporosis; Finite element analysis; Models, anatomic; Biomechanics