The Influence of Thread Tap Mismatch on Pedicle Screw Pullout Strength.

Objective  We aimed to study the "in vitro" pullout strength of SpineGuard/Zavation Dynamic Surgical Guidance Z-Direct Screw (DSG Screw, SpineGuard Inc, Boulder, Colorado, USA), a screw designed to be inserted using a direct insertion technique. Methods  Dynamic Surgical Guidance Screws of 5.5 and 6.5 mm were introduced into polyurethane blocks with a density of 10 PCF (0,16g/cm 3 ). According to the experimental group, screws were inserted without pilot hole, with pilot without tapping, undertapping and line-to-line tapping. Screw pullout tests were performed using a universal test machine after screw insertion into polyurethane blocks. Results  Screws inserted directly into the polyurethane blocks without pilot hole and tapping showed a statistically higher pullout strength. Insertion of the screw without tapping or with undertapping increases the pullout screw strength compared with line-to-line tapping. Conclusion  Dynamic Surgical Guidance Screw showed the highest pullout strength after its insertion without pilot hole and tapping.