title: Femoral head lag screw position for cephalomedullary nails:  a biomechanical analysis.
abstract: OBJECTIVE
  The purpose of this study was to determine if lag screw position affects the biomechanical properties of a cephalomedullary nail used to fix an unstable peritrochanteric fracture.
  
  
  METHODS
  Unstable peritrochanteric fractures were created in 30 synthetic femurs and repaired with Long Gamma 3 Nails using one of 5 lag screw positions: superior, inferior, anterior, posterior, or central. Radiographic measurements including tip-apex distance and a calcar referenced tip-apex distance were calculated from anteroposterior and lateral radiographs. Specimens were tested for axial, lateral bending, and torsional stiffness and then loaded to failure in the axial position. Analysis of variance and linear regression were used for statistical analysis.
  
  
  RESULTS
  The inferior lag screw position had significantly greater mean axial stiffness than superior (P < 0.01), anterior (P = 0.02), and posterior (P = 0.04) positions. Analysis revealed significantly less mean torsional stiffness for the superior lag screw position compared with other lag screw positions (P < 0.01 all 4 pairings). No statistical differences were noted for lateral bending stiffness. Superior and central lag screw positions had significantly greater mean load-to-failure than anterior (P < 0.01 and P = 0.02) and posterior (P < 0.01 and P = 0.05) positions. There were significant negative linear correlations between stiffness with distance from the calcar on anteroposterior radiographs and load-to-failure with distance from the center of femoral neck on the lateral radiographs.
  
  
  CONCLUSIONS
  The inferior lag screw position produced the highest axial and torsional stiffness. Anterior and posterior lag screw positions produced the lowest stiffnesses and load-to-failure. Inferior placement of the lag screw on the anteroposterior radiograph and central placement on the lateral radiographs is recommended.
authors.affiliation: Division of Orthopaedics, Department of Surgery, University of Toronto, Toronto, Ontario, Canada. paul.kuzyk@utoronto.ca
authors.forename: Paul R T
authors.initials: PR
authors.lastname: Kuzyk
authors.forename: Rad
authors.initials: R
authors.lastname: Zdero
authors.forename: Suraj
authors.initials: S
authors.lastname: Shah
authors.forename: Michael
authors.initials: M
authors.lastname: Olsen
authors.forename: James P
authors.initials: JP
authors.lastname: Waddell
authors.forename: Emil H
authors.initials: EH
authors.lastname: Schemitsch
mesh_terms: D001696:Biomechanical Phenomena; D001858:Bone Nails; D001863:Bone Screws; D004548:Elasticity; D019544:Equipment Failure Analysis; D005270:Femur Head / Q000601:surgery*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation* / Q000379:methods*; D006620:Hip Fractures / Q000601:surgery*; D006801:Humans; D011475:Prosthesis Failure; D013314:Stress, Mechanical