title: Influence of screw augmentation in posterior dynamic and rigid stabilization systems in osteoporotic lumbar vertebrae: a biomechanical cadaveric study.
abstract: METHODS
  Biomechanical cadaveric study.
  
  
  OBJECTIVE
  To determine whether augmentation positively influence screw stability or not.
  
  
  BACKGROUND
  Implantation of pedicle screws is a common procedure in spine surgery to provide an anchorage of posterior internal fixation into vertebrae. Screw performance is highly correlated to bone quality. Therefore, polymeric cement is often injected through specifically designed perforated pedicle screws into osteoporotic bone to potentially enhance screw stability.
  
  
  METHODS
  Caudocephalic dynamic loading was applied as quasi-physiological alternative to classical pull-out tests on 16 screws implanted in osteoporotic lumbar vertebrae and 20 screws in nonosteoporotic specimen. Load was applied using 2 different configurations simulating standard and dynamic posterior stabilization devices. Screw performance was quantified by measurement of screwhead displacement during the loading cycles. To reduce the impact of bone quality and morphology, screw performance was compared for each vertebra and averaged afterward.
  
  
  RESULTS
  All screws (with or without cement) implanted in osteoporotic vertebrae showed lower performances than the ones implanted into nonosteoporotic specimen. Augmentation was negligible for screws implanted into nonosteoporotic specimen, whereas in osteoporotic vertebrae pedicle screw stability was significantly increased. For dynamic posterior stabilization system an increase of screwhead displacement was observed in comparison with standard fixation devices in both setups.
  
  
  CONCLUSIONS
  Augmentation enhances screw performance in patients with poor bone stock, whereas no difference is observed for patients without osteoporosis. Furthermore, dynamic stabilization systems have the possibility to fail when implanted in osteoporotic bone.
authors.forename: Sven
authors.initials: S
authors.lastname: Hoppe
authors.affiliation: *Department of Orthopaedic Surgery, Inselspital, University of Bern, Bern, Switzerland †RMS Foundation, Bettlach, Switzerland ‡Laboratory of Biomechanics, ETHZ, Zurich, Switzerland; and §Clinic Sonnenhof, Bern, Switzerland.
authors.forename: Hoppe
authors.initials: H
authors.lastname: Sven
authors.forename: Yannick
authors.initials: Y
authors.lastname: Loosli
authors.forename: Loosli
authors.initials: L
authors.lastname: Yannick
authors.forename: Daniel
authors.initials: D
authors.lastname: Baumgartner
authors.forename: Baumgartner
authors.initials: B
authors.lastname: Daniel
authors.forename: Paul
authors.initials: P
authors.lastname: Heini
authors.forename: Heini
authors.initials: H
authors.lastname: Paul
authors.forename: Lorin
authors.initials: L
authors.lastname: Benneker
authors.forename: Benneker
authors.initials: B
authors.lastname: Lorin
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001843:Bone Cements / Q000627:therapeutic use; D001863:Bone Screws; D002102:Cadaver; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008422:Materials Testing; D019637:Orthopedic Procedures / Q000009:adverse effects / Q000295:instrumentation*; D010024:Osteoporosis / Q000150:complications* / Q000473:pathology / Q000503:physiopathology; D011475:Prosthesis Failure; D012307:Risk Factors; D013314:Stress, Mechanical
chemical_list: D001843:Bone Cements