The Relationship Between Insertional Torque and Pullout Strength of Surgical Screws

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Abstract

Objectives:

To investigate the role of maximal insertional torque (Tmax) of surgical screws and pullout strength (POS) in human cadaveric tibiae.

Methods:

Self-tapping surgical screws (4.5 mm) were inserted into 9 segments of cadaveric tibial cortical bone, measuring Tmax and POS of screws inserted at 50%, 70%, 90%, and 100% Tmax. Computed tomography was also performed, allowing calculation of bone mineral density (BMD) in K2HPO4 concentration (mg/mL) and cortical thickness (mm).

Results:

POS measurements were highest and similar in screws inserted at 70% and 90% of the established Tmax. Screws inserted at 90% Tmax offered a significantly different POS than those inserted at 100% Tmax. No significant differences were found between samples in BMD or cortical thickness. No significant correlations were found between cortical thickness or BMD and Tmax.

Conclusions:

Surgeons should tighten screws to a torque less than Tmax to avoid loss of purchase of the screw and reduced POS.

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