title: Open versus closed halo rings: comparison of fixation strengths.
abstract: OBJECTIVE
  A mechanical skull model was used to compare axial loads to failure for three marketed and one experimental halo ring.
  
  
  BACKGROUND
  Open-back halo rings have become increasingly popular; however, to the authors' best knowledge the literature provides no comparison of the fixation strength of an open-back halo versus the traditional closed design.
  
  
  METHODS
  A model biomechanically similar to a human skull was used to compare the axial force necessary to distract each of four halo rings to failure. Three clinically used halo rings were compared: a closed titanium ring, an open titanium ring, and an open graphite ring. One additional open titanium halo ring was constructed with an angular profile; this ring was compared with the clinically used halos.
  
  
  RESULTS
  The mean force to failure for the closed titanium ring significantly exceeded that for the open rings (P < 0.005). No significant differences were noted among the open halo rings.
  
  
  CONCLUSIONS
  The data obtained by use of this biomechanical model show that the closed halo ring provides distraction strength greater than that of the open rings, suggesting a more rigid system with the closed device. Use of an angular halo did not improve fixation strength in the open ring device. These findings may support use of a closed halo ring in cervical spine traction and immobilization, if this greater strength is shown to be sufficiently clinically important to offset any disadvantages of a closed ring.
authors.affiliation: Shriners Hospitals for Children-Houston, Houston, Texas 77030, USA. jlerman@shrinenet.org
authors.forename: J A
authors.initials: JA
authors.lastname: Lerman
authors.forename: R J
authors.initials: RJ
authors.lastname: Haynes
mesh_terms: D001858:Bone Nails; D004868:Equipment Failure; D019544:Equipment Failure Analysis; D006108:Graphite; D007103:Immobilization; D008953:Models, Anatomic; D009989:Orthotic Devices; D012886:Skull / Q000502:physiology / Q000601:surgery*; D013314:Stress, Mechanical; D013718:Tensile Strength / Q000502:physiology; D014025:Titanium; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D006108:Graphite; D014025:Titanium