title: Comparison of the axial stiffness of carbon composite and aluminium alloy circular external skeletal fixator rings.
abstract: OBJECTIVE
  The purpose of this study was to compare the axial stiffness of aluminium alloy and carbon composite single-ring constructs.
  
  
  METHODS
  Single-ring constructs were made with rings of different material compositions (aluminium alloy and carbon composite), diameters (55 mm, 85 mm, and 115 mm), and thicknesses (6 mm for the single-ring, 12 mm for the double-ring) with all other components remaining constant. Stiffness of each construct was determined under loading in axial compression with a materials testing machine. The axial stiffness of each group was compared using a three-factor factorial analysis of variance investigating all main effects and interactions between ring diameter, ring thickness, and ring material composition; p <0.05 was considered significant.
  
  
  RESULTS
  Carbon composite constructs were 16-55% as stiff as corresponding aluminium alloy constructs. Within each combination of ring material composition and ring diameter, stiffness did not significantly increase when the ring thickness was doubled. Within each combination of ring material composition and ring thickness, stiffness significantly decreased with increased ring diameter.
  
  
  CONCLUSIONS
  Aluminium alloy rings were found to be significantly stiffer than carbon composite rings. Although the carbon composite rings were considerably less stiff, clinical recommendations cannot be made from a single-ring in vitro analysis. Further studies are needed to evaluate the behaviour of these rings in vivo.
authors.affiliation: College of Veterinary Medicine Biomedical Sciences, Colorado State University, Fort Collins, CO 80523-1678, USA. Chris.Gauthier@colostate.edu
authors.forename: C M
authors.initials: CM
authors.lastname: Gauthier
authors.forename: M P
authors.initials: MP
authors.lastname: Kowaleski
authors.forename: P D
authors.initials: PD
authors.lastname: Gerard
authors.forename: G L
authors.initials: GL
authors.lastname: Rovesti
mesh_terms: D000818:Animals; D016267:External Fixators / Q000662:veterinary*; D008422:Materials Testing; D019563:Mechanics