Does the Type of Tap Utilized Impact Biomechanical Performance of Cervical Pedicle Screws? A Comparison of Pre-Tapping with an Awl versus Drill in a Biomimetic Model

Introduction: Pedicle screws are an important aspect of treatment for numerous spine pathologies. There are several methods of preparing bone for pedicle screw insertion, including awls and drills. To the best of our knowledge, the biomechanical characteristics of these have not been directly compared in the past. Given that an awl displaces bone within the prepared screw insertion track whereas a drill can result in bone removal, we hypothesized that pedicle screws inserted after preparation with an awl would demonstrate improved biomechanical performance.

Methods: Twenty biomimetic spine models mimicking cervical spine pedicles were prepared for pedicle screw insertion using either a size-matched awl (n = 10) or hand powered drill (n = 10). Insertional torque, maximum pullout strength on load to failure testing, stiffness, and strain were measured for each group. Performance between the groups was. Differences were considered to be significant for any p-value less than 0.05.

Results: 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).

Conclusion : In this biomimetic spine model, insertional torque and maximum pullout strength were greater in screws placed after preparation with an awl as compared to those prepared with a hand powered drill. Preparing bone for screw insertion using an awl may yield improved biomechanical performance. However, additional follow-up studies are necessary before definitive clinical recommendations can be advised.