title: Enhancing pedicle screw fixation in the aging spine with a novel bioactive bone cement: an in vitro biomechanical study.
abstract: METHODS
  A paired biomechanical study of pedicle screws augmented with bone cement in a human cadaveric and osteoporotic lumbar spine model. OBJECTIVES.: To evaluate immediate strength and stiffness of pedicle screw fixation augmented with a novel bioactive bone cement in an osteoporotic spine model and compare it with polymethylmethacrylate (PMMA) cement.
  
  
  BACKGROUND
  A novel bioactive bone cement, containing nanoscale particles of strontium and hydroxyapatite (Sr-HA), can promote new bone formation and osteointegration and provides a promising reinforcement to the osteoporotic spine. Its immediate mechanical performance in augmenting pedicle screw fixation has not been evaluated.
  
  
  METHODS
  Two pedicle screws augmented with Sr-HA and PMMA cement were applied to each of 10 isolated cadaveric L3 vertebrae. Each screw was subjected to a toggling test and screw kinematics were calculated. The pedicle screw was subjected to a pullout test until failure. Finally, the screw coverage with cement was measured on computed tomographic images.
  
  
  RESULTS
  Screw translations in the toggling test were consistently larger in the Sr-HA group than in the PMMA group (1.4 ± 1.2 mm vs. 1.0 ± 1.1 mm at 1000 cycles). The rotation center was located closer to the screw tip in the Sr-HA group (19% of screw length) than in the PMMA group (37%). The only kinematic difference between Sr-HA and PMMA cements was the screw rotation at 1000 cycles (1.5° ± 0.9° vs. 1.3° ± 0.6°; P = 0.0026). All motion parameters increased significantly with more loading cycles. The pullout force was higher in the PMMA group than the Sr-HA group (1.40 ± 0.63 kN vs. 0.93 ± 0.70 kN), and this difference was marginally significant (P = 0.051). Sr-HA cement covered more of the screw length than PMMA cement (79 ± 19% vs. 43 ± 19%) (P = 0.036).
  
  
  CONCLUSIONS
  This paired-design study identified some subtle but mostly nonsignificant differences in immediate biomechanical fixation of pedicle screws augmented with the Sr-HA cement compared with the PMMA cement.
authors.affiliation: Department of Orthopaedics, University of British Columbia and Vancouver Coastal Health Research Institute, Vancouver, British Columbia, Canada.
authors.forename: Qingan
authors.initials: Q
authors.lastname: Zhu
authors.forename: Stephen
authors.initials: S
authors.lastname: Kingwell
authors.forename: Zhaoyang
authors.initials: Z
authors.lastname: Li
authors.forename: Haobo
authors.initials: H
authors.lastname: Pan
authors.forename: William W
authors.initials: WW
authors.lastname: Lu
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Oxland
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001843:Bone Cements; D001863:Bone Screws; D002102:Cadaver; D017886:Durapatite; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000295:instrumentation* / Q000379:methods; D010024:Osteoporosis / Q000503:physiopathology / Q000601:surgery*; D019904:Polymethyl Methacrylate; D016059:Range of Motion, Articular
chemical_list: D001843:Bone Cements; C509320:strontium-containing hydroxyapatite; D019904:Polymethyl Methacrylate; D017886:Durapatite