title: Antegrade versus retrograde titanium elastic nail fixation of pediatric distal-third femoral-shaft fractures: a mechanical study.
abstract: OBJECTIVE
  To determine whether the stability of elastic stable intramedullary nail (ESIN) constructs differ in terms of antegrade versus retrograde insertion for the fixation of pediatric distal-third transverse femoral-shaft fractures.
  
  
  METHODS
  Ten synthetic composite adolescent-sized femur models and 20 flexible titanium (Ti) intramedullary (IM) nails were divided into antegrade and retrograde groups. A simulated transverse fracture was created in each of 10 models in the distal-third region of the shaft (more precisely near the distal fifth). The fractures were then stabilized with ESIN. The specimens were subjected to four-point bending and then axial torsion. Flexural forces were applied to the medial aspect of the model across the fracture site at a rate of 0.05 mm/s to a maximum displacement of 3.7 mm (7 degrees). Torsional moments were applied to the distal aspect of the model in internal and external rotation at a rate of 0.75 degrees/s to a maximum of 10 degrees. Loads and stiffnesses were determined between consistent displacement limits; differences were compared using t tests (alpha = 0.05, two tailed).
  
  
  RESULTS
  Flexural stiffness was significantly greater in the retrograde group (350 +/- 72 N/mm) compared with antegrade (195 +/- 95 N/mm; P = 0.02). A 66-kg load placed across the fracture displaced the site 3.7 mm for the antegrade group, whereas the retrograde group required a load 89% greater (125 kg). Although torsional stiffness tended to be greater in the antegrade group, the differences were not statistically significant (P = 0.2).
  
  
  CONCLUSIONS
  Although the recommendation for distal-third femur fractures is antegrade nail insertion, this study demonstrates that given satisfactory cortical starting points in the distal fragment, retrograde insertion provides greater stability. These mechanical testing data are the first to address this specific fracture scenario and may aid surgical decision making.
authors.affiliation: Division of Pediatric Orthopaedic Surgery, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, Cincinnati, OH 45229, USA. charles.mehlman@cchmc.org
authors.forename: Charles T
authors.initials: CT
authors.lastname: Mehlman
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Nemeth
authors.forename: David L
authors.initials: DL
authors.lastname: Glos
mesh_terms: D000293:Adolescent; D001696:Biomechanical Phenomena; D001858:Bone Nails; D005264:Femoral Fractures / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000379:methods*; D006801:Humans; D008953:Models, Anatomic; D016059:Range of Motion, Articular; D014025:Titanium
chemical_list: D014025:Titanium