• Randi Rotne, Nicky Bertollo, William Walsh, Navneet K Dhand, Katja Voss, and Kenneth A Johnson.
• Faculty of Veterinary Science, University of Sydney, NSW 2006, Australia. Electronic address: ranrot@icloud.com.
• Injury. 2014 Mar 1;45(3):515-21.

IntroductionThe maintenance of friction between locking plates and bone is not essential, so that they can be applied with a gap between the plate and underlying bone. We hypothesised that the presence of a gap under a locking plate with a conical coupling mechanism would reduce fixation stability or allow uncoupling of the locking screws from the plate.Materials And MethodsLocking plates with two conically coupled locking screws were applied to 6 pairs of adult canine femora. One of each pair had plate to bone contact and the contralateral construct had a 2 mm plate to bone gap. Constructs were cyclically loaded in cantilever bending with 10 percent incremental increases every 1000 cycles at 2 Hz, starting at 250 N. The constructs were fatigued to failure. To evaluate fatigue life of the conical coupling, testing was repeated with aluminium tubing replacing the bone, to eliminate screw-bone cutout failure.ResultsThe mean sustained loads and cycles to failure in the contact group (420.80, standard error [SE] 14.97 N; 7612.00, SE 574.70 cycles) were significantly greater than in the gap group (337.50, SE 14.97 N; 4252.00, SE 574.70 cycles), (p<0.001). Failure mode of all bone constructs was via screw cutout from the bone. Aluminium tubing constructs failed via screw or plate fatigue and breaking, with one construct having elevation of the plate over the screw head.Discussion And ConclusionsElevation of locking plates with a conical coupling system by 2 mm from the bone reduced construct fatigue life but did not result in screw head uncoupling from the plate.Copyright © 2013 Elsevier Ltd. All rights reserved.

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