The thermal profile of self-tapping screws: The effect of insertion speed, power insertion, and screw geometry on heat production at the bone-screw interface

Abstract

Introduction: Power insertion of screws using high-speed saves time during operative fixation of fractures compared to manual insertion. Heat production during screw insertion may cause thermal damage at the critical bone-screw interface, reducing fixation strength, delaying healing, or increasing infection risk. Currently, the thermal impact of screw insertion is incompletely understood. This study investigated the thermal profiles of self-tapping screws at varying insertion speeds, utilizing manual versus power insertion, and with differing cutting flute geometries to determine which variables may save time while mitigating thermal injury.

Methods: Thermal and mechanical force profiles were obtained during insertion of 24 mm length, 3.5 mm stainless steel screws into 50 PCF polyurethane after pre-drilling. Power insertion at low (30RPM) and high (300RPM) speed, manual screwdriver insertion versus high-speed power insertion, and two different cutting flute geometries were compared. Infrared thermography was used to measure maximum surface temperatures and mean temperature change (°C). Time (s) was measured to compare manual and power insertion. Means were compared using a two-tailed independent t-test.

Results: Maximum surface temperature of high-speed insertion (55.42 ± 5.58 °C) was significantly greater (p < 0.001) than low-speed (41.07 ± 2.33 °C). Similarly, mean temperature rise of high-speed insertion (29.52 ± 5.39 °C) was greater than that of low-speed (15.13 ± 2.63 °C) (p < 0.001). There was no statistical difference in maximum surface temperature between manually inserted screws (56.58 ± 5.53 °C) and high-speed power inserted screws (55.42 ± 5.58 °C) (p = 0.155), while insertion speeds were almost 5 times faster with high-speed power insertion (6.75 ± 1.84 s) than with manual insertion (30.3 ± 4.06 s) (p < 0.001). There were no differences detected between the geometry groups in any outcome measure tested.

Conclusion: High speeds for screw insertion generate significantly greater maximum temperatures and greater temperature rise than slower speeds. Surprisingly, the thermal profile of manual insertion was similar to high-speed insertion, while requiring significantly longer for insertion. Low-speed insertion generated significantly lower maximal temperatures and temperature rise. Surgeons could consider utilizing low-speed when inserting orthopaedic screws with a power driver to minimize thermal impact to bone while optimizing efficiency.

Keywords: Geometry; Heat; Insertion; Power; Self-tapping screw; Thermal.