title: Biomechanical evaluation of an expandable nail for the fixation of midshaft fractures.
abstract: BACKGROUND
  The objective of this study was to compare the torsional stability of diaphyseal long bone fractures fixed with either a Fixion nail (DiscOTech, Monroe Township, NJ) or a standard locked Zimmer M/DN locked nail (Zimmer, Warsaw, IN).
  
  
  METHODS
  Two fracture models were used to evaluate the bone-implant constructs. A transverse osteotomy was created in all tibiae, and a spiral fracture was created in all humeri. Paired specimens were randomly assigned to receive either a Fixion or Zimmer M/DN locked nail. Each implanted construct was cyclically loaded in torsion, and construct stiffness for each fracture type and each bone computed from the resulting load-displacement curves.
  
  
  RESULTS
  Performance of the Fixon nail in the tibial transverse model was variable: 2 of 10 implanted constructs failed during testing, and average construct stiffness was significantly greater for the Zimmer nail. No significant difference was found between the stiffness of the Zimmer M/DN and Fixion implanted humeral constructs either with or without the interlock.
  
  
  CONCLUSIONS
  Fracture type significantly affected the performance of the Fixion nail. Our results suggest that the Fixion nail is most suitable for use in fractures where torsional loads across the fracture site are shared between the nail and the bony ends of the fracture, as in a spiral fracture.
authors.affiliation: Department of Biomechanics, Hospital for Special Surgery, New York, NY, USA.
authors.forename: Suzanne A
authors.initials: SA
authors.lastname: Maher
authors.forename: Kathleen
authors.initials: K
authors.lastname: Meyers
authors.forename: Olivier
authors.initials: O
authors.lastname: Borens
authors.forename: Michael
authors.initials: M
authors.lastname: Suk
authors.forename: Andrew
authors.initials: A
authors.lastname: Grose
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Wright
authors.forename: David
authors.initials: D
authors.lastname: Helfet
mesh_terms: D001696:Biomechanical Phenomena; D001858:Bone Nails; D004867:Equipment Design; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation*; D006801:Humans; D006810:Humeral Fractures / Q000503:physiopathology / Q000601:surgery*; D012399:Rotation; D013978:Tibial Fractures / Q000503:physiopathology / Q000601:surgery*; D019415:Torque; D014102:Torsion Abnormality