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33rd Annual Scientific Meeting proceedings

Stream:   |   Session: Short Communications Orthopaedic + Neuro
Date/Time: 07-07-2023 (16:45 - 17:00)   |   Location:
What price do we pay for off-axis placement of a locking screw? A Biomechanical Comparison of a 3.5 mm Fixed-Angle and 3.5 mm Variable-Angle Stainless Steel Locking Plate System
Kaczmarek JK*1, Bartkowiak TB2, Paczos PP2, Zawadzki PZ2, Laczna DN2, Gapinski BG2
1Vetacare - Dr. Philipp Winkels, Erftstadt, Germany, 2Poznan University of Technology, Poznan, Poland.

Locking plates (LP) differ from each other in the design of the locking mechanism. The goal of this study was to investigate the effect of screw insertion-angle (SIA) and insertion-torque (IT) for two different LP.

Materials and Methods
A 3.5mm Locking Compression Plate (LCP) and 3.5mm Polyaxial Locking System (PLS) were compared in a destructive mechanical screw push-out test. The screws were inserted into the plate at 0°, 5°, and 10° in the LCP-Group (n=4 per insertion-angle); and at 0°, 5°, 10°, 15°, and 20° in the PLS-Group; (n=4 per insertion angle). Insertion-torque was set to 1.5 and 2.5 Nm. A Micro-CT was performed to quantify the amount of thread-contact. Shapiro-Wilk and post hoc Bonferroni were performed to compare IT- and SIA-effect on push-out strength (POS) between groups.

Push-out strength was higher for the LCP-Group compared to the PLS-Group at 0° SIA regardless of the IT. Off-axis insertion of screws significantly decreased the POS in the LCP-Group (p < 0.05). A higher IT significantly increased the screw POS for the LCP (p < 0.05), but not for the PLS. The PLS had the highest POS when the screws were at 0° (p < 0.05) at any given IT. Increasing the SIA in both systems reduced the thread-contact within the plate hole.

The mechanical properties of PLS are more affected by SIA than by IT, whereas LCP properties are affected by both. Placing LCP locking screws off-axis, significantly reduces the screw-holding strength; therefore, it should be avoided.

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