Biomechanical comparison of subaxial cervical lateral mass screws with pilot hole creation utilizing an awl versus a fluted hand drill in a validated biomimetic 3D printed spine model

- Rebecca DeCarlo , Andrew Rees, Austin Allen, Samuel Chewning, Michael Bohl


Lateral mass screws are a frequently utilized method for achieving fixation of the subaxial cervical spine. One relatively unexplored research topic involves how different methods of pilot hole preparation influence the biomechanical performance of screws. An awl displaces bone within the prepared pilot track whereas a drill results in bone removal. This study was conducted at the Carolina Neurosurgery and Spine Biomechanics lab with validated biomimetic 3D printed bone models. A subaxial cervical lateral mass with outer layer of cortical bone and inner cancellous bone was designed for the experiment and 20 models were printed. Pilot holes were prepared using an awl in 10 models and a hand drill in 10 models prior to insertion of lateral mass screws. Insertional torque, maximum pullout strength, stiffness, and strain were measured for each group. Mean insertional torque was significantly greater in screws placed after preparation with an awl (24.6 Ncm) as compared to a hand drill (18.1 Ncm) (p = 0.0002). Maximum pullout strength on load to failure testing was significantly greater in screws placed after preparation with an awl (315.6 N) versus those prepared with a hand drill (271.4 N) (p < 0.0001). There was no significant difference in stiffness (awl 292.2 N/mm versus drill 250.8 N/mm, p = 0.18) or strain (awl 332.3 Nmm versus drill 270.6 Nmm, p = 0.24). Results from this study in a biomimetic cervical pedicle model suggest that preparing pilot holes for screw insertion using an awl may yield improved biomechanical performance.