title: Biomechanical comparison of plate and screw fixation in anterior pelvic ring fractures with low bone mineral density.
abstract: BACKGROUND
  Osteosynthesis of anterior pubic ramus fractures can be challenging, especially in poor bone quality. The aim of the present study was to compare plate and retrograde endomedullary screw fixation of the superior pubic ramus with low bone mineral density (BMD).
  
  
  METHODS
  Twelve human cadaveric hemi-pelvises were analyzed in a matched pair study design. BMD of the specimens was 35±30mgHA/cm(3), as measured in the fifth lumbar vertebra. A simulated two-fragment superior pubic ramus fracture model was fixed with either a 7.3-mm cannulated retrograde screw (Group 1) or a 10-hole 3.5-mm reconstruction plate (Group 2). Cyclic progressively increasing axial loading was applied through the acetabulum. Relative interfragmentary movements were captured using an optical motion tracking system.
  
  
  RESULTS
  Initial axial construct stiffness was 424±116.1N/mm in Group 1 and 464±69.7N/mm in Group 2, with no significant difference (p=0.345). Displacement and gap angle at the fracture site during cyclic loading were significantly higher in Group 1 compared to Group 2. Cycles to failure, based on clinically relevant criteria, were significantly lower in Group 1 (3469±1837) compared to Group 2 (10,226±3295) (p=0.028). Failure mode in Group 1 was characterized by screw cutting through the cancellous bone. In Group 2 the specimens exclusively failed by plate bending.
  
  
  CONCLUSIONS
  From biomechanical point of view, pubic ramus stabilization with plate osteosynthesis is superior compared to a single retrograde screw fixation in osteoporotic bone. However, the extensive surgical approach needed for plating must be considered.
authors.affiliation: AO Research Institute Davos, Clavadelerstr. 8, 7270 Davos, Switzerland. Electronic address: yvespascal.acklin@gmail.com.
authors.forename: Yves P
authors.initials: YP
authors.lastname: Acklin
authors.affiliation: AO Research Institute Davos, Clavadelerstr. 8, 7270 Davos, Switzerland.
authors.forename: Ivan
authors.initials: I
authors.lastname: Zderic
authors.affiliation: AO Research Institute Davos, Clavadelerstr. 8, 7270 Davos, Switzerland.
authors.forename: Jan
authors.initials: J
authors.lastname: Buschbaum
authors.affiliation: AO Research Institute Davos, Clavadelerstr. 8, 7270 Davos, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Varga
authors.affiliation: AO Research Institute Davos, Clavadelerstr. 8, 7270 Davos, Switzerland.
authors.forename: Jason A
authors.initials: JA
authors.lastname: Inzana
authors.affiliation: University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Grechenig
authors.affiliation: AO Research Institute Davos, Clavadelerstr. 8, 7270 Davos, Switzerland.
authors.forename: R Geoff
authors.initials: RG
authors.lastname: Richards
authors.affiliation: AO Research Institute Davos, Clavadelerstr. 8, 7270 Davos, Switzerland.
authors.forename: Boyko
authors.initials: B
authors.lastname: Gueorguiev
authors.affiliation: University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany.
authors.forename: Paul
authors.initials: P
authors.lastname: Schmitz
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation / Q000379:methods; D006801:Humans; D008422:Materials Testing; D058866:Osteoporotic Fractures / Q000601:surgery*; D010384:Pelvic Bones / Q000293:injuries / Q000601:surgery*; D016474:Weight-Bearing
keywords: Biomechanical testing; Pelvic fracture; Retrograde endomedullary screw fixation; Superior pubic ramus fixation