title: Mechanical Evaluation of Four Internal Fixation Constructs for Scaphoid Fractures.
abstract: BACKGROUND
  The objective of this study was to compare the mechanical performance of 4 different constructs for fixation of oblique scaphoid fractures.
  
  
  METHODS
  Twenty-eight synthetic scaphoids underwent an oblique osteotomy along the dorsal sulcus. Each was randomly assigned to fixation by 1 of 4 methods: two 1.5-mm headless compression screws, one 2.2-mm screw, one 3-mm screw, or a 1.5-mm volar variable-angle plate. After fixation, scaphoids were potted at a 45° angle and loaded at the distal pole by a hydraulically driven mechanical testing system plunger until the fixation failed. Excursion and load were measured with a differential transformer and load cell, respectively. From these data, the stiffness, load-to-failure, and maximum displacement of each construct were calculated.
  
  
  RESULTS
  The 2.2-mm screw demonstrated the highest stiffness and the two 1.5-mm screws had the lowest. However, there were no significant differences among the fixation methods in terms of stiffness. Both 2.2- and 3-mm screw constructs had significantly higher loads-to-failure than two 1.5-mm screws. The maximum load for the plate approached, but did not achieve, statistical significance compared with the 1.5-mm screws. There was no significant difference among constructs in displacement.
  
  
  CONCLUSIONS
  All constructs demonstrated similar mechanical properties that may provide sufficient stability for effective clinical use. Given their significantly higher loads-to-failure, a 2.2- or 3-mm screw may be superior to two 1.5-mm screws for fixation of unstable scaphoid fractures. The volar plate did not have superior mechanical characteristics to the compression screws.
authors.affiliation: NYU Hospital for Joint Diseases, New York, NY, USA.
authors.forename: Bryan G
authors.initials: BG
authors.lastname: Beutel
authors.affiliation: NYU Hospital for Joint Diseases, New York, NY, USA.
authors.forename: Eitan
authors.initials: E
authors.lastname: Melamed
authors.affiliation: NYU Hospital for Joint Diseases, New York, NY, USA.
authors.forename: Richard M
authors.initials: RM
authors.lastname: Hinds
authors.affiliation: NYU Hospital for Joint Diseases, New York, NY, USA.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Gottschalk
authors.affiliation: NYU Hospital for Joint Diseases, New York, NY, USA.
authors.forename: John T
authors.initials: JT
authors.lastname: Capo
keywords: fracture; internal fixation; mechanics; scaphoid