Biomechanical Analysis of Pedicle Screw Reinsertion Along the Same Trajectory in a Validated 3D Printed Synthetic Bone Model

Abstract

To investigate the biomechanical properties of pedicle screw reinsertion along the same trajectory in a previously validated synthetic bone model. Twenty identical acrylonitrile butadiene styrene models of a lumbar vertebrae were 3D-printed. Screws were placed in the standard fashion into each pedicle. Models were separated into two equal groups, control and experimental. Experimental group screws were completely removed from their testing block and reinserted once. All screws in both groups were then forcibly removed. Continuous torque monitoring was collected on screw insertion (IT), removal (RT), and reinsertion (RIT). Pullout strength (PO), screw stiffness (STI), and strain energy (STR) were calculated. There was no significant difference between control and experimental groups for PO (p = 0.26), STI (p = 0.55), STR (p = 0.50), or IT (p = 0.24). There was a significant decrease in RIT (54.5 N-cm ± 8.2 N-cm) from control IT (62.9 N-cm ± 8.4 N-cm, p = 0.045) and experimental IT (67.5 N-cm ± 7.6 N-cm, p = 0.0026). Strong correlations (Pearson's r > 0.80) were seen between control IT against STR and PO, between each of the experimental torque measurements, and between experimental PO and STI. Despite a significant decrease in insertion torque, there is no significant loss of pedicle screw performance when a screw is removed and reinserted along the same trajectory.