Pull-out strength of screws in long bones at different insertion angles: finite element analysis and experimental investigations

Different types of plates are available to allow insertion of screws for internal fixation of long bone fractures. The aim of the study was to determine the effect of the insertion of screws at different angles on a long bone to the pull-out strength. Using 3D printed bone models, we tested the pull-out strength of screws in long bones at insertion angles between 0 and 40° with both finite element analysis and on printed models experimentally and compared the results. Test samples and cortical screws used were modeled with SolidWorks software and analyzed with Ansys software. As the screw insertion angle increases, the pull-out forces on the test specimens increase from 61.14 ± 3.5 N at 0° to 273 ± 6.8 N at 40° with an exception of a small drop between 15 and 20° from 235.4 ± 6.2 to 233 ± 6.9 N. Both methods showed an increase in the pull-out strength of screws as the insertion angle increases. This might be applicable in the clinical practice of bone fixation. Further studies on plate and screw fixation are needed to complement the findings.