Abstract
BackgroundWe examined the biomechanical performance of a three-dimensional (3D)-printed vertebra on pedicle screw insertional torque (IT), axial pullout (APO), and stiffness (ST) testing.Materials and methodsSeventy-three anatomically identical L5 vertebral body models (146 pedicles) were printed and tested for IT, APO, and ST using single-threaded pedicle screws of equivalent diameter (6.5 mm), length (40.0 mm), and thread pitch (2.6 mm). Print properties (material, cortical thickness [number of shells], cancellous density [in-fill], in-fill pattern, print orientation) varied among models. One-way analysis of variance was performed to evaluate the effects of variables on outcomes.ResultsThe type of material significantly affected IT, APO, and ST (P < 0.001, all comparisons). For acrylonitrile butadiene styrene (ABS) models, in-fill density (25-35%) had a positive linear association with APO (P = 0.002), ST (P = 0.008), and IT (P = 0.10); similarly for the polylactic acid (PLA) models, APO (P = 0.001), IT (P < 0.001), and ST (P = 0.14). For the nylon material type, in-fill density did not affect any tested parameter. For a given in-fill density, material, and print orientation, the in-fill pattern significantly affected IT (P = 0.002) and APO (P = 0.03) but not ST (P = 0.23). Print orientation also significantly affected IT (P < 0.001), APO (P < 0.001), and ST (P = 0.002).Conclusions3D-printed vertebral body models with specific print parameters can be designed to perform analogously to human bone on pedicle screw tests of IT, APO, and ST. Altering the material, in-fill density, in-fill pattern, and print orientation of synthetic vertebral body models could reliably produce a model that mimics bone of a specific bone mineral density.
Highlights
The Barrow Biomimetic Spine project aims to create a 3-dimensional (3D)-printed, synthetic spine model with high anatomical and biomechanical fidelity compared to that of a human cadaveric spine
For acrylonitrile butadiene styrene (ABS) models, in-fill density (25-35%) had a positive linear association with axial pullout (APO) (P = 0.002), ST (P = 0.008), and insertional torque (IT) (P = 0.10); for the polylactic acid (PLA) models, APO (P = 0.001), IT (P < 0.001), and ST (P = 0.14)
The models used in this study were printed using three different materials: acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and nylon
Summary
The Barrow Biomimetic Spine project aims to create a 3-dimensional (3D)-printed, synthetic spine model with high anatomical and biomechanical fidelity compared to that of a human cadaveric spine. Polyurethane foam is a commonly used synthetic bone model, and it has been widely reported as a reasonable substitute for cadaveric bone [4,5,6,7,8]. Existing synthetic models such as polyurethane are regulated and standardized per guidelines of the American Society for Testing and Materials (ASTM-1839-08), with various grades of foam correlating to specific bone mineral densities (BMDs) [9]. We examined the biomechanical performance of a three-dimensional (3D)-printed vertebra on pedicle screw insertional torque (IT), axial pullout (APO), and stiffness (ST) testing
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