title: Biomechanical comparison of the Herbert and AO cortical bone screws for compression of an equine third carpal bone dorsal plane slab osteotomy.
abstract: OBJECTIVE
  To assess feasibility of insertion of 4.5-mm Herbert cannulated bone screws (HS) using fluoroscopic guidance and compare the mechanical shear strength of these HS and 4.5-mm AO cortical bone screws (AO) for fixation of dorsal plane slab osteotomies in equine cadaver third carpal bones (C3).
  
  
  METHODS
  Eight equine cadavers.
  
  
  METHODS
  Bone mineral composition and density of contralateral C3 were confirmed to be equivalent using dual-energy x-ray absorptiometry. A standard 10-mm C3 slab osteotomy was reduced using HS or AO instrumentation under fluoroscopic guidance. Specimens were loaded in shear until failure, using a materials testing apparatus.
  
  
  RESULTS
  HS and AO instrumentation allowed accurate reconstruction of the osteotomy, but there was difficulty encountered seating the HS proximal self-tapping threads. There was no significant difference in maximal load to failure, stiffness, or mode of failure of constructs created with the HS and AO screws.
  
  
  CONCLUSIONS
  Use of 4.5-mm HS for repair of C3 radial facet, dorsal plane slab fractures may result in a mechanically comparable fixation to a repair using a 4.5-mm AO. Equine dorsal C3 may be too dense, however, to allow placement of the proximal self tapping threads of the HS without potentially excessive application of torque to the screw itself.
  
  
  CONCLUSIONS
  Dorsal plane, radial facet slab fractures of the equine C3 are a significant clinical problem. Accurate reconstruction and stabilization are necessary for return to athletic function.
authors.affiliation: Centre for Equine Studies, Suffolk, England.
authors.forename: R C
authors.initials: RC
authors.lastname: Murray
authors.forename: E M
authors.initials: EM
authors.lastname: Gaughan
authors.forename: R M
authors.initials: RM
authors.lastname: Debowes
authors.forename: J J
authors.initials: JJ
authors.lastname: Hoskinson
mesh_terms: D015502:Absorptiometry, Photon / Q000662:veterinary; D000818:Animals; D015519:Bone Density / Q000502:physiology; D001863:Bone Screws / Q000662:veterinary*; D002102:Cadaver; D002350:Carpus, Animal / Q000000981:diagnostic imaging / Q000502:physiology / Q000601:surgery*; D005260:Female; D005471:Fluoroscopy / Q000379:methods / Q000662:veterinary; D006736:Horses / Q000601:surgery*; D008297:Male; D010027:Osteotomy / Q000379:methods / Q000662:veterinary*; D013523:Surgical Equipment / Q000662:veterinary