title: Titanium versus stainless steel for anterior spinal fusions: an analysis of rod stress as a predictor of rod breakage during physiologic loading in a bovine model.
abstract: METHODS
  In vitro biomechanical evaluation of rod stress during physiologic loading of anterior scoliosis instrumentation.
  
  
  OBJECTIVE
  To determine effects of material properties and rod diameter on rod stresses in anterior scoliosis instrumentation.
  
  
  BACKGROUND
  Relationships between instrumentation dimensions, materials, and potential rod failure in anterior scoliosis instrumentation remain unclear.
  
  
  METHODS
  Eighteen immature bovine spines were randomized to 3 groups: 1) 4.0-mm stainless steel, 2) 5.0-mm stainless steel, and 3) 4.75-mm titanium alloy. Spines underwent physiologic tests in flexion-extension, lateral bending, and torsion. Rod surface strains were converted to rod stress and normalized to each material's yield stress. Construct stiffness and the normalized rod stresses were compared with a one-way ANOVA (P < 0.05).
  
  
  RESULTS
  The 4.0-mm steel and 4.75-mm titanium construct stiffness was similar across all tests. The 5.0-mm steel system was significantly stiffer than 4.0-mm steel (lateral bending/torsion) and 4.75-mm titanium (torsion/flexion) constructs. Rod surface stress was significantly lower for the 4.75-mm titanium rod compared with 4.0-mm and 5.0-mm steel rods for all tests.
  
  
  CONCLUSIONS
  The percentage of yield stress was lowest for the 4.75-mm Ti rod for all tests due to titanium's greater yield stress. This suggests the 4.75-mm rod has a lower fatigue failure risk than either steel construct.
authors.affiliation: Department of Orthopedics, Children's Hospital, San Diego, San Diego, CA, USA.
authors.forename: Michelle
authors.initials: M
authors.lastname: Wedemeyer
authors.forename: Stefan
authors.initials: S
authors.lastname: Parent
authors.forename: Andrew
authors.initials: A
authors.lastname: Mahar
authors.forename: Tim
authors.initials: T
authors.lastname: Odell
authors.forename: Troy
authors.initials: T
authors.lastname: Swimmer
authors.forename: Peter
authors.initials: P
authors.lastname: Newton
mesh_terms: D000818:Animals; D002417:Cattle; D008422:Materials Testing / Q000379:methods / Q000592:standards*; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods / Q000592:standards*; D013193:Stainless Steel / Q000592:standards*; D013314:Stress, Mechanical; D014025:Titanium / Q000592:standards*; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D013193:Stainless Steel; D014025:Titanium