title: The effect of posterior sag on the fixation stability of intertrochanteric hip fractures.
abstract: BACKGROUND
  This study evaluates the effects of posterior sag on the fixation stability of intertrochanteric hip fractures.
  
  
  METHODS
  A simulated, two-part intertrochanteric fracture was created in human cadaveric femurs. One of each pair was stabilized using a sliding hip screw in anatomic reduction and the other in 30 degrees of posterior sag. Measurements for load versus inferior head displacement, gapping, and shearing were made in axial and torsional loading.
  
  
  RESULTS
  Initial axial and torsional loading showed no significant differences between the two groups. During cyclic loading, the osteotomy gap in the posteriorly angulated specimens decreased by 0.11 cm at 10 cycles (p = 0.006) and by 0.22 cm at 10,000 cycles (p = 0.33), corresponding to a 2-degree and 6-degree reduction in sag angle. Axial stiffness differed between the two groups: 10.3 N/mm for anatomic versus 6.7 N/mm (p = 0.002) for posteriorly angulated specimens. Loading to failure demonstrated no significant differences between the two groups.
  
  
  CONCLUSIONS
  This study demonstrated that 30 degrees of posterior sag does not result in a significant difference in construct strength or stability.
authors.affiliation: Musculoskeletal Research Institute, Hospital for Joint Diseases Orthopaedic Institute, New York, New York 10003, USA.
authors.forename: Thomas N
authors.initials: TN
authors.lastname: Joseph
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Chen
authors.forename: Frederick J
authors.initials: FJ
authors.lastname: Kummer
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Koval
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000009:adverse effects*; D002102:Cadaver; D004867:Equipment Design; D005269:Femur / Q000000981:diagnostic imaging / Q000601:surgery; D005593:Fracture Fixation, Internal / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D006620:Hip Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D011859:Radiography