title: Biomechanical stability of single-screw versus two-screw fixation of an unstable slipped capital femoral epiphysis model: effect of screw position in the femoral neck.
abstract: OBJECTIVE
  To biomechanically evaluate single screw and varying 2 screw fixations for an unstable slipped capital femoral epiphysis (SCFE) model using physiologically relevant loading.
  
  
  METHODS
  In vitro biomechanical study.
  
  
  METHODS
  Twenty-four immature porcine proximal femurs were prepared to simulate a mild-to-moderate unstable SCFE. The femurs were randomized into 4 fixation groups: single screw, 2 screws horizontally placed, 2 screws vertically placed, and 2 oblique screws. Biomechanical testing determined maximum load to failure (N), load (N) at 2, 4, 6, and 8 mm of femoral head displacement, and stiffness (newtons per millimeter) for each group.
  
  
  RESULTS
  No significant differences were found among the 3 different 2 screw configurations. The 2 screw constructs were 66% stiffer and 66% stronger than the single screw construct. In addition, whereas there was no difference at 2 mm of femoral head displacement, each subsequent displacement (4, 6, and 8 mm) demonstrated significantly higher failure loads when 2 screws were used for stabilization.
  
  
  CONCLUSIONS
  Slipped capital femoral epiphysis stabilization with 2 screws leads to increased stability over single screw fixation; however, none of the 3 configurations/placement patterns of the 2 screw constructs seemed to be superior in fixation stability.
  
  
  CONCLUSIONS
  These data support the use of a 2 screw construct in acute/unstable SCFE fixation. The biomechanical benefit of 2 screws needs to be considered in the face of greater potential for inadvertent penetration into the joint with an increased number of screws.
authors.affiliation: Department of Orthopaedics, Children's Hospital, San Diego, CA, USA.
authors.forename: Shyam
authors.initials: S
authors.lastname: Kishan
authors.forename: Vidyadhar
authors.initials: V
authors.lastname: Upasani
authors.forename: Andrew
authors.initials: A
authors.lastname: Mahar
authors.forename: Richard
authors.initials: R
authors.lastname: Oka
authors.forename: Tim
authors.initials: T
authors.lastname: Odell
authors.forename: Michael
authors.initials: M
authors.lastname: Rohmiller
authors.forename: Peter
authors.initials: P
authors.lastname: Newton
authors.forename: Dennis
authors.initials: D
authors.lastname: Wenger
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001863:Bone Screws; D004195:Disease Models, Animal; D004839:Epiphyses, Slipped / Q000503:physiopathology / Q000601:surgery*; D005272:Femur Neck; D005471:Fluoroscopy; D006621:Hip Joint / Q000503:physiopathology / Q000601:surgery*; D019637:Orthopedic Procedures / Q000379:methods*; D013552:Swine