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Objective To study numerical model for calculating the insertion torque of bone screw. Methods The three stages of screw insertion process for the self-tapping screw were analyzed, so as to make mechanical modeling and simulation calculation on torque and torque angle at screw forming stage. Meanwhile, the insertion experiments of screws with specification of φ2.9×12 from three manufactures on polyurethane test blocks with different grades were performed according to ASTM F543-17(YY/T 1506-2016), and the experimental results were compared with the calculated ones. Results The deviations between the predicted insertion torque by the model and the measured torque in the experiments were 5 mN·m and 12 mN·m within the acceptable error range, which were 10% smaller than the average measured torque in the experiments. Conclusions The developed mechanical calculation model can be used to simulate and predict the insertion torque of medical bone screws in research and development or clinical use, and its combination with in vitro mechanical experiments provides an effective way of developing and designing bone screws.
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As an effective implant for bone fracture, bone screws are widely used in clinic. Based on the clinical application of bone screws, this study summarized different kinds of bone screws according to their structures and materials, analyzed 3 kinds of common screw failure (loosening, breaking, corrosion) and the influencing factors. The common testing methods of screws were summarized, especially the key points and difficulties during the testing process for bone screws were analyzed, which was important for improving the design of product, selection of materials and development of in vitro testing technology. The development trend for testing method of bone screws was prospected as well.
RESUMO
Objective To explore the optimal screw fixation of anterior column lag screw fixation in the treatment of acetabular anterior column fractures by finite element method.Methods Firstly,CT scanning images from one healthy adult volunteer (male 30),were transferred into Materialise Mimics Innovation Suite 16.0 software,then three-dimensional (3D) models of pelvic were reconstructed and stored in stereolithography format.Then Imageware 12.0 software (EDS,USA) was used to produce the optimal and safe channel of the screw for acetabulum anterior column fixation.Three types of screw fixation were generated,i.e.(1) geometric algorithm screw channel,(2) in-out-in channel,(3) free screw channel.Secondly,all model data were transferred into Ansys 12.0 software to establish the finite element model.Gravity load were defined as 600 N,1 200 N,and 2 400 N,and the Von Mises the parameters of peak stress and deformation were recorded.Results Respectively load of 600 N,1 200 N,2 400 N force to normal hip and geometric algorithm screw channel, in-out-inscrew channel,free screw channel,the comparison between groups of hip by stress and hip deformation,with a given loading force of hip by stress and hip deformation increase gradually,the two were positively correlated,including screw by stress at slightly higher than that of normal hip,while the stress of hip by geometric algorithm screw channel andin-out-inscrew channel were similar,and that by free screw channel increased significantly.There was no significant difference between groups in the hip deformation.With a given loading force (600 N,1 200 N,2 400 N) on geometric algorithm screw channel、 in-out-inscrew channel and free screw channel,the deformation is gradually increased,and there were positively correlated.With the stress on geometric algorithm screw channel,it was significantly reduced compared with the latter two,and in-out-in screw channel suffered the biggest stress.Conclusion Through the finite element analysis,the geometric algorithm screw channel can be used as a safe and effective way for acetabulum anterior column fracture.