title: A biomechanical comparison of headless tapered variable pitch and AO cortical bone screws for fixation of a simulated lateral condylar fracture in equine third metacarpal bones.
abstract: OBJECTIVE
  To compare drilling, tapping, and screw-insertion torque, force, and time for the 4.5-mm AO and 6.5-mm Acutrak Plus (AP) bone screws, and to compare the mechanical shear strength and stiffness of a simulated complete lateral condylar fracture of the equine third metacarpal bone (MC3) stabilized with either an AO or AP screw.
  
  
  METHODS
  In vitro biomechanical assessment of screw-insertion variables, and shear failure tests of a bone-screw-stabilized simulated lateral condylar fracture.
  
  
  METHODS
  Eight pairs of cadaveric equine MC3s
  
  
  METHODS
  Metacarpi were placed in a fixture and centered on a biaxial load cell in a materials-testing system to measure torque, compressive force, and time for drilling, tapping, and screw insertion. Standardized simulated lateral condylar fractures were stabilized by either an AO or AP screw and tested in shear until failure. A paired t test was used to assess differences between screws, with significance set at P < .05.
  
  
  RESULTS
  Insertion and mechanical shear testing variables were comparable for AO and AP insertion equipment and screws.
  
  
  CONCLUSIONS
  The 6.5-mm tapered AP screw can be inserted in equine third metacarpal condyles and is mechanically comparable with the 4.5-mm AO screw for fixation of a simulated lateral condylar fracture.
  
  
  CONCLUSIONS
  Considering the comparable mechanical behavior, the potential for less-persistent soft-tissue irritation with the headless design, and the ability to achieve interfragmentary compression by inserting the screw in one hole drilled perpendicular to the fracture plane, the 6.5-mm tapered AP screw may be an attractive alternative for repair of incomplete lateral condylar fractures in horses.
authors.affiliation: J. D. Wheat Veterinary Orthopedic Research Laboratory, School of Veterinary Medicine,University of California, Davis, CA, USA.
authors.forename: L D
authors.initials: LD
authors.lastname: Galuppo
authors.forename: S M
authors.initials: SM
authors.lastname: Stover
authors.forename: D G
authors.initials: DG
authors.lastname: Jensen
authors.forename: N H
authors.initials: NH
authors.lastname: Willits
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000662:veterinary*; D002102:Cadaver; D002350:Carpus, Animal / Q000293:injuries* / Q000601:surgery; D004867:Equipment Design / Q000662:veterinary; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation / Q000379:methods / Q000662:veterinary*; D050723:Fractures, Bone / Q000601:surgery / Q000662:veterinary*; D006736:Horses / Q000293:injuries / Q000601:surgery*; D008297:Male; D011897:Random Allocation