title: Fatigue performance of angle-stable tibial nail interlocking screws.
abstract: OBJECTIVE
  Tibial nail interlocking screw failure often occurs during delayed fracture consolidation or at early weight bearing of nailed unstable fractures, in general when high implant stress could not be reduced by other means. Is there a biomechanical improvement in long-term performance of angle stable locking screws compared to conventional locking screws for distal locking of intramedullary tibial nails?
  
  
  METHODS
  Surrogate bones of human tibiae were cut in the distal third and distal locking of the 10 mm intramedullary tibial nail was performed with either two angle stable locking screws or two conventional locking screws in the mediolateral plane. Six specimens per group were mechanically tested under quasi-static and cyclic axial loading with constantly increasing force.
  
  
  RESULTS
  Angle stable locking screw constructs exhibited significantly higher stiffness values (7,809 N/mm ± 647, mean ± SD) than conventional locking screw constructs (6,614 N/mm ± 859, p = 0.025). Angle stable locking screw constructs provided a longer fatigue life, expressed in a significantly higher number of cycles to failure (187,200 ± 18,100) compared to conventional locking screw constructs (128,700 ± 7,000, p = 0.004).
  
  
  CONCLUSIONS
  Fatigue performance of locking screws can be ameliorated by the use of angle stable locking screws, being especially important if the nail acts as load carrier and an improved stability during fracture healing is needed.
authors.affiliation: AO Research Institute Davos, Davos-Platz, Switzerland. mark.lenz@aofoundation.org
authors.forename: Mark
authors.initials: M
authors.lastname: Lenz
authors.forename: Boyko
authors.initials: B
authors.lastname: Gueorguiev
authors.forename: Robert Geoff
authors.initials: RG
authors.lastname: Richards
authors.forename: Thomas
authors.initials: T
authors.lastname: Mückley
authors.forename: Gunther Olaf
authors.initials: GO
authors.lastname: Hofmann
authors.forename: Dankward
authors.initials: D
authors.lastname: Höntzsch
authors.forename: Markus
authors.initials: M
authors.lastname: Windolf
mesh_terms: D001696:Biomechanical Phenomena; D001858:Bone Nails; D001863:Bone Screws; D002102:Cadaver; D004867:Equipment Design; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation*; D006801:Humans; D011474:Prosthesis Design; D011475:Prosthesis Failure; D018709:Statistics, Nonparametric; D013314:Stress, Mechanical; D013978:Tibial Fractures / Q000601:surgery*