title: An in vitro biomechanical comparison of a 5.5 mm locking compression plate fixation with a 4.5 mm locking compression plate fixation of osteotomized equine third metacarpal bones.
abstract: OBJECTIVE
  To compare the monotonic biomechanical properties and fatigue life of a 5.5-mm-broad locking compression plate (5.5 LCP) fixation with a 4.5-mm-broad locking compression plate (4.5 LCP) fixation to repair osteotomized equine 3rd metacarpal (MC3) bones.
  
  
  METHODS
  In vitro biomechanical testing of paired cadaveric equine MC3 with a middiaphyseal osteotomy, stabilized by 1 of 2 methods for fracture fixation.
  
  
  METHODS
  Fifteen pairs of adult equine cadaveric MC3 bones.
  
  
  METHODS
  Fifteen pairs of equine MC3 were divided into 3 test groups (5 pairs each) for (1) 4-point bending single cycle to failure testing, (2) 4-point bending cyclic fatigue testing, and (3) torsional single cycle to failure testing. An 8-hole, 5.5 LCP was applied to the dorsal surface of 1 randomly selected bone from each pair and an 8-hole, 4.5 LCP was applied dorsally to the contralateral bone from each pair using a combination of cortical and locking screws. All plates and screws were applied using standard ASIF techniques. All MC3 bones had middiaphyseal osteotomies. Mean test variable values for each method were compared using a paired t-test within each group with significance set at P<.05.
  
  
  RESULTS
  Mean yield load, yield bending moment, composite rigidity, failure load, and failure bending moment, under 4-point bending, single cycle to failure, of the 5.5 LCP fixation were significantly greater than those of the 4.5 LCP fixation. Mean cycles to failure in 4-point bending of the 5.5 LCP fixation (170,535+/-19,166) was significantly greater than that of the 4.5 LCP fixation (129,629+/-14,054). Mean yield load, mean composite rigidity, and mean failure load under torsional testing, single cycle to failure was significantly greater for the broad 5.5 LCP fixation compared with the 4.5 LCP fixation. In single cycle to failure under torsion, the mean+/-SD values for the 5.5 LCP and the 4.5 LCP fixation techniques, respectively, were: yield load, 151.4+/-19.6 and 97.6+/-12.1 N m; composite rigidity, 790.3+/-58.1 and 412.3+/-28.1 N m/rad; and failure load: 162.1+/-20.2 and 117.9+/-14.6 N m.
  
  
  CONCLUSIONS
  The 5.5 LCP was superior to the 4.5 LCP in resisting static overload forces (palmarodorsal 4-point bending and torsional) and in resisting cyclic fatigue under palmarodorsal 4-point bending.
  
  
  CONCLUSIONS
  These in vitro study results may provide information to aid in selection of an LCP for repair of equine long bone fractures.
authors.affiliation: Equine Health Studies Program, Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA. gsod@vetmed.lsu.edu
authors.forename: Gary A
authors.initials: GA
authors.lastname: Sod
authors.forename: Laura M
authors.initials: LM
authors.lastname: Riggs
authors.forename: Colin F
authors.initials: CF
authors.lastname: Mitchell
authors.forename: George S
authors.initials: GS
authors.lastname: Martin
authors.forename: Marjorie S
authors.initials: MS
authors.lastname: Gill
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001860:Bone Plates / Q000662:veterinary*; D006736:Horses / Q000601:surgery*; D066298:In Vitro Techniques; D050279:Metacarpal Bones / Q000601:surgery*; D010027:Osteotomy / Q000662:veterinary*; D054159:Torsion, Mechanical; D016474:Weight-Bearing