title: Biomechanical evaluation of fixation strength of conventional and expansive pedicle screws with or without calcium based cement augmentation.
abstract: BACKGROUND
  The expansive pedicle screw was originally developed to be installed in the bone of compromised quality, but there are some concerns whether it can provide enough fixation strength in the spine with osteoporosis or severe osteoporosis.
  
  
  METHODS
  Twelve fresh human cadaver spines were stratified into four levels: normal, osteopenia, osteoporosis and severe osteoporosis. The vertebra was bilaterally instrumented with pedicle screws according to four protocols, including conventional pedicle screw without augmentation, expansive pedicle screw without augmentation, conventional screw with augmentation and expansive screw with augmentation. Screw pullout tests were conducted.
  
  
  RESULTS
  Given the same specimen, the fixation strength of expansive screw was significantly higher than that of the conventional screw. When the same type of screw was used, the fixation strength of the calcium based cement augmented group was stronger than that of the non-augmented group. The pullout strength and stiffness of the expansive screw, augmented conventional screw and augmented expansive screw groups at the osteoporotic level were comparable to those of the conventional pedicle screw group at the osteopenic level. However, under the severely osteoporotic bone environment, the pullout strength of pedicle screw with whatever placement protocol was significantly lower than that of the conventional screw group at the osteopenic level.
  
  
  CONCLUSIONS
  Our results demonstrate that (i) the expansive pedicle screw appears feasible and safe in either osteopenic or osteoporotic spine; (ii) calcium based cement augmentation can offer improved initial fixation strength of pedicle screws.; and (iii) no screw placement protocol we examined is efficacious in the bone at the severely osteoporotic level.
authors.affiliation: Department of Orthopaedics, Xijing Hospital, Fourth Military Medical University, No. 17 West Changle Road, Xi'an, Shaanxi Province, China.
authors.forename: Mingxuan
authors.initials: M
authors.lastname: Gao
authors.forename: Wei
authors.initials: W
authors.lastname: Lei
authors.forename: Zixiang
authors.initials: Z
authors.lastname: Wu
authors.forename: Da
authors.initials: D
authors.lastname: Liu
authors.forename: Lei
authors.initials: L
authors.lastname: Shi
mesh_terms: D001843:Bone Cements / Q000627:therapeutic use*; D001863:Bone Screws; D002102:Cadaver; D002484:Cementation / Q000379:methods; D019544:Equipment Failure Analysis; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D017276:Friction; D006801:Humans; D008297:Male; D008875:Middle Aged; D010024:Osteoporosis / Q000503:physiopathology* / Q000601:surgery*; D011474:Prosthesis Design; D013131:Spine / Q000503:physiopathology* / Q000601:surgery*; D013718:Tensile Strength; D016896:Treatment Outcome
chemical_list: D001843:Bone Cements