title: Ex vivo evaluation of the biomechanical effect of varying monocortical screw numbers on a plate-rod canine femoral gap model.
abstract: OBJECTIVE
  To compare the biomechanical behaviour of plate-rod constructs with varying numbers of monocortical screws applied to an ex vivo canine femoral-gap ostectomy model.
  
  
  METHODS
  Twenty Greyhound dog cadaveric femurs.
  
  
  METHODS
  Bone mineral density (BMD) was assessed with dual x-ray absorptiometry. Bones were assigned to four groups. Bones had a 12-hole 3.5 mm locking compression plate with one bicortical non-locking cortical screw in the most proximal and distal plate holes and an intramedullary Steinmann pin applied across a 20 mm mid-diaphyseal ostectomy. Additionally, one to four monocortical non-locking cortical screws were then placed (Groups 1-4 respectively) in the proximal and distal fragments. Stiffness and axial collapse were determined before and after cyclic axial loading (6000 cycles at 20%, 40%, and 60% of mean bodyweight [total: 18000 cycles]). Constructs subsequently underwent an additional 45000 cycles at 60% of bodyweight (total: 63000 cycles). Loading to failure was then performed and ultimate load and mode of failure recorded.
  
  
  RESULTS
  The BMD did not differ significantly between groups. Construct stiffness for group 1 was significantly less than group 4 (p = 0.008). Stiffness showed a linear increase with an increasing number of monocortical screws (p = 0.001). All constructs survived fatigue loading. Load-to-failure was not significantly different between groups. Mean load- to-failure of all groups was >1350N.
  
  
  CONCLUSIONS
  Ex vivo canine large-breed femurs showed adequate stability biomechanically and gradually increasing stiffness with increasing monocortical screw numbers.
authors: School of Veterinary Science, University of Bristol, Langford House, Langford, Bristol, UK. peter.delisser@bristol.ac.uk
authors: P J
authors: PJ
authors: Delisser
authors: G P
authors: GP
authors: McCombe
authors: R S
authors: RS
authors: Trask
authors: J A
authors: JA
authors: Etches
authors: A J
authors: AJ
authors: German
authors: S L
authors: SL
authors: Holden
authors: A M
authors: AM
authors: Wallace
authors: N J
authors: NJ
authors: Burton
mesh_terms: D015502:Absorptiometry, Photon; D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density; D001860:Bone Plates / Q000662:veterinary*; D001863:Bone Screws / Q000662:veterinary*; D002102:Cadaver; D004285:Dogs; D005269:Femur / Q000601:surgery*