title: Orthogonal pin construct versus parallel uniplanar pin constructs for pelvic external fixation: a biomechanical assessment of stiffness and strength.
abstract: OBJECTIVE
  The purpose of this study is to compare the structural stiffness of an orthogonal pelvic external fixator pin construct with 2 different parallel external fixator pin constructs in a simulated bone model.
  
  
  OBJECTIVE
  An orthogonal pelvic external fixator pin construct would be significantly more stiff than a parallel pin construct when loaded in-plane under similar conditions.
  
  
  METHODS
  Thirty synthetic pelvic bone models were configured with orthogonal pins (group 1), parallel iliac crest pins (group 2), or parallel supra-acetabular pins (group 3). Specimens were loaded either in-plane (flexion/extension moment) or out-of-plane (internal/external rotation moment) to assess construct stiffness.
  
  
  METHODS
  Orthopaedic industry mechanical testing laboratory (Stryker Orthopedics, Mahwah, NJ).
  
  
  METHODS
  Single load cycle to failure with load application modified to assess stiffness both in-plane and out-of-plane with the pin constructs.
  
  
  METHODS
  Pelvic external fixation pin construct stiffness.
  
  
  RESULTS
  Stiffness for in-plane loading was 150.2 +/- 51.2 N/mm for the orthogonal pin construct, 105.0 +/- 46.9 N/mm for the iliac crest pin construct, and 104.7 +/- 20.7 N/mm for the supra-acetabular pin construct. Pairwise comparisons demonstrated that the difference was significant (P < 0.05) between groups 1 and 2 and groups 1 and 3 but not between groups 2 and 3. Stiffness for out-of-plane loading was 49.6 +/- 3.4 N/mm for the orthogonal pin construct, 53.9 +/- 3.5 N/mm for the iliac crest pin construct, and 100.6 +/- 4.3 N/mm for the supra-acetabular pin construct, with significant differences (P < 0.05) between groups 1 and 3 and groups 2 and 3 but not between groups 1 and 2.
  
  
  CONCLUSIONS
  An orthogonal pelvic external fixator pin construct produced a significantly stiffer construct for in-plane loading (flexion/extension moment) compared with either parallel pin construct; however, a parallel supra-acetabular pin construct was stiffer for out-of-plane loading.
authors.affiliation: Department of Orthopaedic Surgery, College of Medicine, University of Cincinnati, Cincinnati, OH 45267-0212, USA. michael.archdeacon@uc.edu
authors.forename: Michael T
authors.initials: MT
authors.lastname: Archdeacon
authors.forename: Sameh
authors.initials: S
authors.lastname: Arebi
authors.forename: T Toan
authors.initials: TT
authors.lastname: Le
authors.forename: Rene
authors.initials: R
authors.lastname: Wirth
authors.forename: Roland
authors.initials: R
authors.lastname: Kebel
authors.forename: Mayur
authors.initials: M
authors.lastname: Thakore
mesh_terms: D001858:Bone Nails; D019245:Compressive Strength; D003198:Computer Simulation; D019544:Equipment Failure Analysis; D016267:External Fixators; D050723:Fractures, Bone / Q000601:surgery*; D006801:Humans; D008954:Models, Biological; D010384:Pelvic Bones / Q000293:injuries / Q000601:surgery*; D018583:Pliability; D011474:Prosthesis Design; D016474:Weight-Bearing