title: Cement augmented anterior odontoid screw fixation is biomechanically advantageous in osteoporotic patients with Anderson Type II fractures.
abstract: METHODS
  A biomechanical human cadaveric study.
  
  
  OBJECTIVE
  The authors tested a cannulated and perforated lag screw and compared in situ polymethylmethacrylate (PMMA) augmentation against nonaugmentation for fixation of osteoporotic type II odontoid fractures.
  
  
  BACKGROUND
  Osteoporosis has been identified as a strong predictor for pseudarthrosis after screw fixation of type II odontoid fractures with cut-out through the anterior wall of C2 as the most frequent mode of implant failure. The concept of PMMA augmentation of the proximal screw shank could serve as a useful supplement in this context.
  
  
  METHODS
  A total of 18 fresh-frozen human cadaveric C2 vertebrae were harvested (median 86.5 y; range, 69-98 y). Reduced bone quality was verified by quantitative computed tomography. Type II odontoid fractures were created and repaired with a cannulated lag screw, which has perforations in the proximal screw shank. Additional PMMA augmentation was carried out for 9 specimens. The position of the screw and cement distribution were evaluated by computed tomography. Values for maximum force to failure, energy to failure, and stiffness were statistically compared between cement augmented and nonaugmented screws.
  
  
  RESULTS
  Cement distribution in the C2 vertebral body was circumferential around the screw shank without leakage into the spinal canal or into the fracture gap in all 9 specimens. The cement augmented screws showed a 2.4 times higher maximum force to failure (363±94 N, P<0.001), a 2.7 times higher energy to failure (1300±698 mJ, P<0.001), and a 1.76 times higher stiffness (90±35 N/mm, P=0.031) in comparison with the nonaugmented screws.
  
  
  CONCLUSIONS
  Cement augmentation for fixation of osteoporotic type II odontoid fractures showed biomechanical advantages. It was also shown that cement augmentation of the newly developed screw is technically easy and safe under in vitro conditions. The technique might be useful with regard to the surgical treatment of elderly patients with osteoporotic odontoid fractures.
authors.affiliation: *Department of Neurosurgery, Jena University Hospital, Friedrich Schiller University Jena, Jena †Institute of Orthopaedic Research and Biomechanics, Ulm University, Ulm ‡Institute of Anatomy and Cell Biology, Martin Luther University Halle, Halle, Germany.
authors.forename: Albrecht
authors.initials: A
authors.lastname: Waschke
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Berger-Roscher
authors.forename: Heike
authors.initials: H
authors.lastname: Kielstein
authors.forename: Christian
authors.initials: C
authors.lastname: Ewald
authors.forename: Rolf
authors.initials: R
authors.lastname: Kalff
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Wilke
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001843:Bone Cements; D001863:Bone Screws; D002102:Cadaver; D006801:Humans; D009809:Odontoid Process / Q000293:injuries* / Q000601:surgery*; D058866:Osteoporotic Fractures / Q000000981:diagnostic imaging / Q000601:surgery*; D019904:Polymethyl Methacrylate; D011183:Postoperative Complications; D011542:Pseudarthrosis / Q000209:etiology; D014057:Tomography, X-Ray Computed
chemical_list: D001843:Bone Cements; D019904:Polymethyl Methacrylate