title: Influence of plate-bone contact on cyclically loaded conically coupled locking plate failure.
abstract: BACKGROUND
  The 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.
  
  
  METHODS
  Locking 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.
  
  
  RESULTS
  The 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.
  
  
  CONCLUSIONS
  Elevation 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.
authors.affiliation: Faculty of Veterinary Science, University of Sydney, NSW 2006, Australia. Electronic address: ranrot@icloud.com.
authors.forename: Randi
authors.initials: R
authors.lastname: Rotne
authors.affiliation: University of NSW, Surgical and Orthopaedic Research Laboratories, Sydney, NSW 2052, Australia. Electronic address: n.bertollo@unsw.edu.au.
authors.forename: Nicky
authors.initials: N
authors.lastname: Bertollo
authors.affiliation: University of NSW, Surgical and Orthopaedic Research Laboratories, Sydney, NSW 2052, Australia. Electronic address: w.walsh@unsw.edu.au.
authors.forename: William
authors.initials: W
authors.lastname: Walsh
authors.affiliation: Faculty of Veterinary Science, University of Sydney, NSW 2006, Australia. Electronic address: navneet.dhand@sydney.edu.au.
authors.forename: Navneet K
authors.initials: NK
authors.lastname: Dhand
authors.affiliation: Faculty of Veterinary Science, University of Sydney, NSW 2006, Australia. Electronic address: katja.voss@sydney.edu.au.
authors.forename: Katja
authors.initials: K
authors.lastname: Voss
authors.affiliation: Faculty of Veterinary Science, University of Sydney, NSW 2006, Australia. Electronic address: kenneth.johnson@sydney.edu.au.
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Johnson
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D019245:Compressive Strength; D004285:Dogs; D019544:Equipment Failure Analysis; D005269:Femur / Q000473:pathology / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000295:instrumentation; D008297:Male; D013314:Stress, Mechanical; D013718:Tensile Strength; D019415:Torque
keywords: Biomechanical; Cadaver; Conical coupling; Cyclic; Fracture; Locking plate; Plate–bone contact; Screw cutout