title: Biomechanical evaluation of a bioresorbable odontoid screw.
abstract: OBJECTIVE
  The authors tested the ability of a resorbable cannulated lag screw composed of a polylactide copolymer to repair Type II odontoid fractures. The resorbable screw was evaluated for its ability to restore strength and stiffness to the fractured odontoid process compared with traditional titanium screws.
  
  
  METHODS
  Type II odontoid fractures were created in 14 human cadaveric C-2 vertebrae by applying a posterolaterally directed load and piston displacement was measured. Seven of these specimens were repaired using metal screws and seven were repaired using resorbable screws. Specimens were reinjured using the same mechanism as the initial fracture. Values of ultimate strength and stiffness during failure were statistically compared between metal and resorbable screws and between initial fracture and reinjury.
  
  
  CONCLUSIONS
  The stiffness and ultimate strength during initial fracture were significantly greater than those during reinjury in specimens repaired using resorbable screws or titanium screws (p < 0.001). The resorbable and titanium screws both restored 31% of the initial ultimate strength of the intact specimen (p = 0.95). The stiffness of the fractured odontoid process was restored to 15 and 23% of its initial value by repair with resorbable and metal screws, respectively (p = 0.07). The mode of failure in resorbable screws was usually breakage or bending, whereas that in metal screws was consistently cutout of the proximal shaft of the screw through the anterior C-2 vertebral body.
authors.affiliation: Department of Neurological Surgery, University of California, San Francisco, California 94122, USA. AmesC@neurosurg.ucsf.edu
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Ames
authors.forename: Neil R
authors.initials: NR
authors.lastname: Crawford
authors.forename: Robert H
authors.initials: RH
authors.lastname: Chamberlain
authors.forename: Vivek
authors.initials: V
authors.lastname: Deshmukh
authors.forename: Belma
authors.initials: B
authors.lastname: Sadikovic
authors.forename: Volker K H
authors.initials: VK
authors.lastname: Sonntag
mesh_terms: D020341:Absorbable Implants; D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D001863:Bone Screws; D019245:Compressive Strength; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005592:Fracture Fixation / Q000295:instrumentation*; D017102:Fracture Healing / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D008875:Middle Aged; D009809:Odontoid Process / Q000293:injuries* / Q000503:physiopathology / Q000601:surgery; D011091:Polyesters; D011183:Postoperative Complications / Q000503:physiopathology*; D016103:Spinal Fractures / Q000503:physiopathology / Q000601:surgery*; D013718:Tensile Strength; D014025:Titanium; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D011091:Polyesters; C033616:poly(lactide); D014025:Titanium