Biomechanical comparison of pullout strengths of five cortical screw types: An innovative measurement method
Ahmet Karakaşlı1, Nihat Acar1, Mehmet Özcanhan2, Fatih Ertem3
1Department of Orthopedics and Traumatology, Medical Faculty of Dokuz Eylul University, İzmir, Turkey
2Department of Computer Engineering, Dokuz Eylul University, Faculty of Engineering, İzmir, Turkey
3Department of Biomechanics, Dokuz Eylul University, Health Science Enstitute, İzmir, Turkey
Keywords: Biomechanical comparison; cortical screws; pullout strength.
Objectives: This study aims to assess five different cortical screw types using artificial femurs, under equated testing conditions. Materials and methods: We investigated the maximum force needed to cause deformation at screw-bone interface using fourth generation composite femurs by conducting separate pullout tests for each screw type. We normalized obtained results with traditional methods and crosscomparison. To conduct pullout tests dependent on screw dimensions, we eliminated the effect of bicortical bone thickness by equalizing the conditions of screw insertion.
Results: Non-locking screws with larger diameter and pitch depth required larger pullout forces to be extracted, showing statistically superior performance compared to locking screws with smaller dimensions. However, the statistical differences between the absolute pullout forces decreased after the traditional normalization of the results. We proposed a new normalization method based on solid geometric reasoning.
Conclusion: This novel approach showed that a screw type that appeared to show average performance, in fact, did not have statistically significantly different results than the top performers. Surgeons are not required to prefer larger dimension screws in small dimension host bones.