title: Augmentation of pedicle screw fixation strength using an injectable calcium sulfate cement: an in vivo study.
abstract: METHODS
  An in vivo landrace model of cement augmentation of pedicle screw was established, and axial pull-out tests and histological analysis were performed.
  
  
  OBJECTIVE
  To investigate the long-term in vivo biomechanical performance of pedicle screws augmented with calcium sulfate cement.
  
  
  BACKGROUND
  Little information is available on the long-term biomechanical performance of pedicle screws augmented with calcium sulfate cement in vivo.
  
  
  METHODS
  Ten pedicle screws were implanted into the lumbar vertebrae of 15 adult females landraces weighing 105 to 115 kg. The pedicle screws were augmented with Polymethyl methacrylate (PMMA), augmented with the calcium sulfate cement, or not augmented. The landraces were randomized into 3 study periods of day 1, 6 weeks, and 12 weeks. At the end of the assigned study periods, the animals were killed and axial pull-out tests and histological analyses were conducted on the isolated specimen vertebrae.
  
  
  RESULTS
  No significant difference was found among the 1-day, 6-week,and 12-week control group (P > 0.18), no significant difference was found among the 1-day, 6-week and 12-week PMMA group (P > 0.59), and no significant difference was found among the 1-day, 6-week and 12-week calcium sulfate group (P > 0.27). The maximum POS of the PMMA groups was significantly greater than that of the calcium sulfate groups (P < 0.002), the maximum POS of the calcium sulfate groups was significantly greater than that of the control groups (P < 0.004). Histologically progressive absorption of the calcium sulfate was evident. The bone walls around the screws in the 12-week calcium sulfate group were statistically significantly thicker than that of the 12-week control group and that of the 12-week PMMA group.
  
  
  CONCLUSIONS
  Results of this study demonstrate that the injectable calcium sulfate cement can significantly improve the immediate POS of pedicle screw fixation, and this effect can be maintained even if the calcium sulfate cement has been absorbed completely, which may result from that the calcium sulfate cement resorption paralleled bone ingrowth.
authors.affiliation: Department of Orthopedic Surgery, Peking University First Hospital, Beijing, China.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Yi
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Hailin
authors.initials: H
authors.lastname: Lu
authors.forename: Chunde
authors.initials: C
authors.lastname: Li
authors.forename: Tianyue
authors.initials: T
authors.lastname: Zhu
mesh_terms: D000818:Animals; D001843:Bone Cements; D001863:Bone Screws; D002133:Calcium Sulfate / Q000008:administration & dosage; D004195:Disease Models, Animal; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D015552:Injections, Intralesional; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D008422:Materials Testing; D016348:Osseointegration; D019904:Polymethyl Methacrylate / Q000008:administration & dosage*; D011859:Radiography; D013123:Spinal Fusion; D013552:Swine; D013718:Tensile Strength
chemical_list: D001843:Bone Cements; D019904:Polymethyl Methacrylate; D002133:Calcium Sulfate