What Is the Cost of Off-Axis Insertion of Locking Screws? A Biomechanical Comparison of a 3.5 mm Fixed-Angle and 3.5 mm Variable-Angle Stainless Steel Locking Plate Systems

Abstract

Objective The aim of this study was to evaluate the effect of screw insertion angle and insertion torque on the mechanical properties of a 3.5 fixed-angle locking plate locking compression plate (LCP) and 3.5 variable-angle locking plate polyaxial locking system (PLS). Methods In the LCP group, screws were placed abaxially at 0, 5 and 10 degrees. In the PLS group, screws were placed at 0, 5, 10, 15 and 20 degrees abaxially. The insertion torque was set to 1.5 and 2.5 Nm in the LCP and PLS groups respectively. A load was applied parallel to the screw axis, and the screw push-out force was measured until the locking mechanism was loosened. Results The 3.5 LCP showed higher push-out strength than the 3.5 PLS when the screws were placed at 0 degree regardless of the insertion torque. The off-axis insertion of 3.5 LCP locking screws resulted in a significant decrease in push-out strength (p < 0.05). A higher insertion torque value significantly increased the screw holding strength for the 3.5 LCP (p < 0.05). The 3.5 PLS system had a significantly higher push-out force when the screws are at 0 degree than at 5, 10 and 15 degrees, and 20 degrees (p < 0.05) at any given insertion torque. An increase in the insertion torque did not have a significant effect on the push-out strength of the 3.5 PLS locking system. Conclusion The 3.5 PLS is more sensitive to the screw insertion angle than to the insertion torque, whereas the 3.5 LCP is affected by both factors. Placing 3.5 LCP locking screws off-axis significantly reduces the screw holding strength; therefore, this approach has to be avoided. The findings of our research indicate that a 1.5 Nm torque can be used for a 3.5 PLS.

Effect of screw insertion angle and speed on the incidence of transcortical fracture development in a canine tibial diaphyseal model

“…The different screw insertion speeds were chosen to emulate the speed settings found on a commercially available orthopedic drill (DeSoutter V‐Drive) 10 . Angles of insertion were chosen to best reflect what we thought would be a reasonable error (up to 10° off axis) to expect in the clinical setting 11,12 . For the purposes of this study, the tibial diaphysis was defined as the portion of bone comprising the middle 70% of the length of the tibia.…”

“…10 Angles of insertion were chosen to best reflect what we thought would be a reasonable error (up to 10 off axis) to expect in the clinical setting. 11,12 For the purposes of this study, the tibial diaphysis was defined as the portion of bone comprising the middle 70% of the length of the tibia.…”

Biomechanical evaluation of variable angle locking systems. A micro-CT analysis.

“…The contact area between the threaded parts of a screw head and plate hole was quantified using micro-CT, which is a method described by Kaczmarek et al 22,23 To perform this measurement, each construct was scanned using a metrological computed tomographic device (vjtomejx s240; GE Sensing & Inspection Technologies GmbH, Wunstorf, Germany). The micro-CT scanning was performed with an x-ray beam power of 30.7 W (205 kV/150 mA), an exposition time of 500 milliseconds per image, and a voxel size of 25.169 mm.…”

Biomechanical Investigation of Bone Screw Head Design for Extracting Stripped Screw Heads: Integration of Mechanical Tests and Finite Element Analyses

“…Improving screw head socket designs to prevent stripping and to increase the torque to facilitate unscrewing remains an unresolved mechanical challenge [5,20]. An incompetently inserted torque may result in unstable fixation, while conversely, a higher insertion torque could lead to cam-out failure or cold welding [19,21]. While complementary instruments, including aiming sleeves, appropriate driver engagement, and torque-limiting devices, may minimize/prevent stripping, such solutions are not reliable and the outcomes are variable [1,22].…”