title: Biomechanical comparison of a 2 and 3 proximal screw-configured antegrade piriformis intramedullary nail with a trochanteric reconstruction nail in an unstable subtrochanteric fracture model.
abstract: OBJECTIVE
  The objective of this study was to test the stiffness and ultimate load to failure of new intramedullary (IM) nail proximal screw configurations as compared to a trochanteric reconstruction nail.
  
  
  METHODS
  Twenty-one synthetic composite femurs were mounted on a Material Testing System and tested in axial compression 5 times. The femurs had an 1 of 2 IM nail types inserted with 1 of 3 proximal screw configurations: a 3-screw configuration with 2 transverse screws and a screw angled into the femoral neck; a 2-screw design with a single transverse screw and a single screw angled into the femoral neck; 2 parallel screws angled into the femoral neck. There were 7 specimens in each group. An unstable fracture (OTA/AO 32-C3.2) was created. and the stiffness of these constructs was tested in compression 5 times. Each construct was then loaded to failure in compression.
  
  
  RESULTS
  The 3-screw construct provided more axial stiffness (214 N/mm +/- 75) than either the 2-screw construct (123 N/mm +/- 32) or the trochanteric reconstruction nail (127 N/mm +/- 21) (P = 0.017 and 0.035 for 3-screw vs. 2-screw and recon respectively, P = 0.45 for 2-screw vs. recon). Load-to-failure testing demonstrated similarity among the different screw configurations (3-screw = 2230 N +/- 265, 2-screw = 2283 N +/- 260, Reconstruction nail = 2121 N +/- 156) (P = 1.0 all groups).
  
  
  CONCLUSIONS
  The proximal 3-screw configuration provided more stiffness than either the 2-screw configuration or trochanteric reconstruction nail. The 2-screw configuration performed equally to a standard trochanteric reconstruction nail in stiffness testing. The ultimate loads to failure for the 3 tested constructs were not significantly different.
authors.affiliation: Department of Orthopaedic Surgery, Saint Louis University School of Medicine, St Louis, MO 63103, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Fissel
authors.forename: Berton R
authors.initials: BR
authors.lastname: Moed
authors.forename: J Gary
authors.initials: JG
authors.lastname: Bledsoe
mesh_terms: D001858:Bone Nails; D001863:Bone Screws; D019245:Compressive Strength; D004867:Equipment Design; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation* / Q000379:methods; D006620:Hip Fractures / Q000601:surgery*; D006801:Humans; D008422:Materials Testing; D008954:Models, Biological; D018583:Pliability