Mechanical Comparison of 3D-Printed Plates and Screws for Open Reduction and Internal Fixation of Fractures

Abstract

Objectives: Three-dimensional (3D) printing has emerged as a promising technology in the field of orthopaedic surgery. The purpose of this study was to evaluate the mechanical properties of 3D printed 1/3 tubular plates and cortical screws compared to standard-of-care stainless steel 1/3 tubular plates and cortical screws. Methods: Replication and modification designs were developed for both plates and screws using open-source computer-assisted design (CAD) software. Models were printed in four materials: acrylonitrile butadiene styrene (ABS), carbon fiber reinforced polylactic acid (PLA), polycarbonate (PC), and polyether ether ketone (PEEK). The implants (Figure 1) were tested and compared to surgical steel plates and screws. Plates were tested with three-point bend and torsional loading using an Instron® material testing machine. Screws were analyzed on pull-out strength in a Sawbones® bone model, shear strength, and torsional loading. Each combination of design and material was placed in its own test group with a sample size (n = 5) and compared to a steel control group (n = 5) for each mechanical test. Results: Significant interaction effects between material type and design type were observed for screw shear (p = 0.003), screw torque (p = 0.023), plate 3-point bend (p = 0.002), and plate torque (p = 0.001). A significant interaction effect was not observed for screw pull-out (p = 0.407), however, a statistically significant difference in mean force between material types (p <0.0005) was observed.Screw Shear: The highest mean force when both material and design were considered was for the CFPLA modified flat design with a mean force of 105.83 N (95% CI 88.51 to 123.14).Screw Torque: The highest mean force when both material and design were considered was for the PEEK modified tilt design with a mean force of 49.51 Ncm (95% CI 43.40 to 55.63).Plate 3-Point Bend: The highest mean force when both material and design were considered was for the PEEK modification design with a mean force of 31.93 N (95% CI 30.53 to 33.33).Plate Torque: The highest mean force when both material and design were considered was for the CFPLA modified flat design with a mean force of 46.88 Ncm (95% CI 42.95 to 50.80).Screw Pull-Out: Mean force produced was highest for PC across all test groups (Figure 2) with a total mean force of 211.86 N (95% CI 186.81 to 236.90). Conclusion: This study demonstrates that desktop 3D printers are capable of printing biocompatible materials that can replicate surgical implants. Although the current materials have significant mechanical variability, they do not approximate the properties of stainless steel. The utility of 3D printed surgical implants for internal fracture fixation provides a potential clinical application in locations where equipment is not as readily available, such as developing countries, forward operating military units, or long duration space flight missions. Furthermore, the cost for 3D printers and 3D printable materials has significantly decreased over recent years. This increase in technology and associated decrease in costs, along with numerous open-source 3D modeling software programs, could provide a low-cost alternative to more expensive and less accessible standard-of-care stainless-steel implants. [Figure: see text]