title: The use of bioabsorbable screws to fix Type II odontoid fractures: a biomechanical study.
abstract: OBJECTIVE
  Anterior screw fixation of the Type II odontoid fracture stabilizes the odontoid without restricting the motion of the cervical spine. The metal screw may limit bone remodeling because of stress shielding (if not placed properly) and limit imaging of the fracture. The use of bioabsorbable screws can overcome such shortcomings of the metal screws. The purpose of this study was to compare the strength of a 5-mm bioabsorbable screw with single 4-mm metal and double 3.5-mm lag screw fixation for Type II fractures of the odontoid process.
  
  
  METHODS
  Three different modalities of anterior screw fixation were used in 19 C-2 vertebrae. These fixation methods consisted of a single 5-mm cannulated bioabsorbable lag screw (Group A), a single 4-mm cannulated titanium lag screw (Group B), and two 3.5-mm cannulated titanium lag screws (Group C). Anteroposterior (AP) stiffness and rotational stiffness were evaluated in all constructs.
  
  
  RESULTS
  There was no statistical difference among the ages of the cadavers in each group (p = 0.52). The AP bending stiffness in Groups A, B, and C was 117 ± 86, 66 ± 43, and 305 ± 130 Nm/mm, respectively. The AP bending stiffness in Group C was significantly higher than that in Groups A and B (p = 0.01 and p = 0.001, respectively). The difference in AP bending stiffness values of bioabsorbable and 4-mm metal screws was not statistically significant (p = 0.23). The rotational stiffness of the double 3.5-mm metal screws was significantly greater than that of the 5-mm bioabsorbable and the 4-mm titanium screws.
  
  
  CONCLUSIONS
  Double screw fixation with 3.5-mm screws provides the stiffest construct in Type II odontoid fractures. Bioabsorbable lag screws (5 mm) have the same AP bending and rotational stiffness as the single titanium lag screw (4 mm) in odontoid fractures.
authors.affiliation: Department of Neurosurgery, Louisiana State University Health Sciences Center, Shreveport, Louisiana, USA.
authors.forename: Ali
authors.initials: A
authors.lastname: Nourbakhsh
authors.forename: Shashikant
authors.initials: S
authors.lastname: Patil
authors.forename: Prasad
authors.initials: P
authors.lastname: Vannemreddy
authors.forename: Alan
authors.initials: A
authors.lastname: Ogden
authors.forename: Debi
authors.initials: D
authors.lastname: Mukherjee
authors.forename: Anil
authors.initials: A
authors.lastname: Nanda
mesh_terms: D020341:Absorbable Implants; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena / Q000502:physiology; D001863:Bone Screws; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009809:Odontoid Process / Q000293:injuries* / Q000601:surgery; D016103:Spinal Fractures / Q000503:physiopathology / Q000601:surgery*