title: PMMA-augmented SI screw: a biomechanical analysis of stiffness and pull-out force in a matched paired human cadaveric model.
abstract: BACKGROUND
  Current literature data and clinical experience show that the number of pelvic fractures continuously rises due to the increasing elderly population. In the elderly with suspected osteoporosis additional implant augmentation with bone cement seems to be an option to avoid secondary displacement. There are no reported biomechanical data in the literature comparing the fixation strength (and anchorage) of standard and augmented SI screws so far. The purpose of this study was to assess the biomechanical performance of cement-augmented versus non-augmented SI screws in a human cadaveric pelvis model.
  
  
  METHODS
  Six human cadaveric pelvises preserved with the method of Thiel were used in this study. Each pelvis was split to a pair of 2 hemi-pelvises, assigned to 2 different groups for instrumentation with one non-augmented or one contralateral cement-augmented SI screw, placed in the body of S1 in a randomized fashion. The osteosynthesis followed a standard procedure with 3D controlled percutaneous iliosacral screw positioning. A biomechanical setup for a quasistatic pullout test of each SI screw was used. Construct stiffness and maximum pullout force were calculated from the load-displacement curve of the machine data. Statistical evaluation was performed at a level of significance p = .05 for all statistical tests.
  
  
  RESULTS
  Stiffness and pullout force in the augmented group (501.6 N/mm ± 123.7, 1336.8 N ± 221.1) were significantly higher than in the non-augmented one (289.7 N/mm ± 97.1, 597.7 N ± 115.5), p = .04 and p = .014, respectively. BMD influenced significantly the pullout force in all study groups.
  
  
  CONCLUSIONS
  Cement augmentation significantly increased the fixation strength in iliosacral screw osteosynthesis of the sacrum in a biomechanical human cadaveric model.
authors.affiliation: Clinic of Trauma Surgery, University of Regensburg, Regensburg 93053, Germany. Electronic address: stephan.grechenig@ukr.de.
authors.forename: Stephan
authors.initials: S
authors.lastname: Grechenig
authors.affiliation: Department of Trauma Surgery, Clinic Wolfsburg, Wolfsburg, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Gänsslen
authors.affiliation: AO Research Institute Davos, Davos, Switzerland.
authors.forename: Boyko
authors.initials: B
authors.lastname: Gueorguiev
authors.affiliation: Clinic of Trauma Surgery, University of Regensburg, Regensburg 93053, Germany.
authors.forename: Arne
authors.initials: A
authors.lastname: Berner
authors.affiliation: Clinic of Trauma Surgery, University of Regensburg, Regensburg 93053, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Müller
authors.affiliation: Clinic of Trauma Surgery, University of Regensburg, Regensburg 93053, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Nerlich
authors.affiliation: Clinic of Trauma Surgery, University of Regensburg, Regensburg 93053, Germany.
authors.forename: Paul
authors.initials: P
authors.lastname: Schmitz
mesh_terms: D001696:Biomechanical Phenomena; D001843:Bone Cements; D001863:Bone Screws; D002102:Cadaver; D002484:Cementation / Q000379:methods; D005593:Fracture Fixation, Internal / Q000379:methods*; D050723:Fractures, Bone / Q000601:surgery*; D006801:Humans; D007085:Ilium / Q000601:surgery*; D016555:Matched-Pair Analysis; D008422:Materials Testing; D010388:Pelvis / Q000601:surgery*; D019904:Polymethyl Methacrylate; D011475:Prosthesis Failure; D012447:Sacrum / Q000601:surgery*; D013314:Stress, Mechanical; D013718:Tensile Strength
chemical_list: D001843:Bone Cements; D019904:Polymethyl Methacrylate
keywords: SI-screw; augmentation; biomechanics; pelvic ring fracture