Publication: Influence of geometrical features of a cortical screw on its bending and pull-out strengths
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Date
2023-07-14
Authors
Mohammad Taufik Hariz bin Rahmat
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Abstract
This final year project focuses on investigating the influence of geometrical features of bone screws on their bending and pull-out strengths. Typically, bone screws are commonly utilized by surgeons as internal fixation devices in orthopedic surgery. However, research has indicated that the failure of the bone screw may cause failure includes breakage and loosening which can lead to loss of fixation and painful bone. Several studies have suggested different solutions, including changing the material of the screw and adjusting how deep the screw is inserted. However, this project aims to determine the bending strength and pull-out strength of bone screws with different geometrical designs, and identify the optimal combination of features to maximize their mechanical properties. The geometrical features of bone screw include screw diameter and thread depth play crucial roles in influencing the mechanical properties of the screws. Three different screws with varying geometrical features were designed using SolidWorks software and fabricated using a 3D printer machine. Both pull-out and bending tests were conducted on these screws to assess their
mechanical properties. The pull-out tests were performed using polyethylene foam blocks with a density of 0.32 g/cm3 as substitutes for bone specimens, ensuring consistent testing conditions and preventing deformation or breakage. The Universal Testing Machine (UTM) Instron 3367 model was used to measure the pull-out and bending strength of the screws, following to the American Standard Testing Method (ASTM) requirements for accuracy and reliability. The results showed that screws with a thread depth of 1.05 mm, which was the highest among the tested screws, had the strongest pull-out strength of 90.65 N. Additionally, in the bending test, screws with larger inner diameters were stiffer and had higher yield strength. The screw with an inner diameter of 4.50 mm, the largest among the screws, demonstrated the highest stiffness of 5.73 N/mm and yield strength of 22.60 MPa.