title: Mechanical study of the safe distance between distal femoral fracture site and distal locking screws in antegrade intramedullary nailing.
abstract: OBJECTIVE
  To determine the safe distance for distal femoral fractures relative to the distal locking screws in antegrade intramedullary femoral nailing using a currently available titanium alloy nail design.
  
  
  METHODS
  Cyclic (fatigue) mechanical testing study.
  
  
  METHODS
  Biomechanics laboratory.
  
  
  METHODS
  Intramedullary nailing of left synthetic fiberglass composite femora with type 32/33-C fractures at 1, 2, 3, and 4 cm from the more proximal of the distal locking screws.
  
  
  METHODS
  The number of loading cycles to failure of the nail.
  
  
  RESULTS
  A load level of 700 N through the femoral mechanical axis was validated as adequate to cause fatigue failure within 200,000 cycles in slotted stainless- steel nails. In the nonslotted titanium alloy nails, this load level caused failure in only 1 of 3 nails with a fracture at 2 cm from the more proximal of the 2 distal locking screws and in 2 of 3 nails with a fracture at 1 cm from the more proximal of the 2 distal locking screws. All of the other nails did not fail >1 million cycles.
  
  
  CONCLUSIONS
  Under laboratory conditions, it is safe to assume that an antegrade titanium alloy nail will survive 1 million compression/bending cycles when the fracture is > or = 3 cm from the more proximal of the 2 distal locking screws.
authors.affiliation: Orthopaedic Bioengineering Laboratory, Department of Orthopaedic Surgery, University of Louisville, Louisville, KY 40202, USA.
authors.forename: Shannon B
authors.initials: SB
authors.lastname: Antekeier
authors.forename: Robert L
authors.initials: RL
authors.lastname: Burden
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Voor
authors.forename: Craig S
authors.initials: CS
authors.lastname: Roberts
mesh_terms: D001696:Biomechanical Phenomena / Q000379:methods; D001858:Bone Nails; D001863:Bone Screws; D019245:Compressive Strength; D004548:Elasticity; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005264:Femoral Fractures / Q000503:physiopathology* / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods*; D006801:Humans; D011475:Prosthesis Failure; D019919:Prosthesis Implantation / Q000379:methods*; D013718:Tensile Strength; D016896:Treatment Outcome