title: Biomechanical study of artificial atlanto-odontoid joint.
abstract: METHODS
  An in vitro biomechanical study.
  
  
  OBJECTIVE
  To determine the initial stability and function of a new artificial joint in a cadaveric cervical spine model by comparing it with a conventional method.
  
  
  BACKGROUND
  Resection of the odontoid and anterior arch of the atlas results in atlantoaxial instability, which if left uncorrected may lead to severe neurologic complications. Currently, such atlantoaxial instability is corrected by anterior and/or posterior C1-C2 fusion.
  
  
  METHODS
  There were 24 fresh human cadaveric cervical spines (C0-C3) randomly divided into 2 groups: group 1, resection of the odontoid with artificial atlanto-odontoid joint (AAOJ); and group 2, resection of the odontoid with Harms anterior atlantoaxial plate (Harms). For each specimen, the intact and resection of the odontoid underwent a flexibility test first, followed by the instrumented construct. Rotational angles of the C0-C3 segment were measured to study the immediate stability and function of resection of the odontoid and AAOJ, compared with the intact and resection of the odontoid and Harms.
  
  
  RESULTS
  Compared with the intact state, resection of the odontoid and AAOJ resulted in a significant decrease in the range of motion (ROM) and neutral zone during flexion, extension, and lateral bending (P < 0.05); however, with regard to axial rotation, there was no significant difference in ROM (P > 0.05). Compared with resection of the odontoid and Harms, resection of the odontoid and AAOJ during flexion, extension, and lateral bending, there was no significant difference in ROM (P > 0.05).
  
  
  CONCLUSIONS
  We have designed a new type of AAOJ for correcting atlantoaxial instability arising from C1 to C2 anterior decompression procedures. The unique aspect of this joint is that it restores, to a great extent, the C1-C2 axial rotation that is lost during current stabilization procedures.
authors.affiliation: Department of Orthopaedic Surgery, Second Hospital of Xi'an Jiaotong University, 159 Xiwulu, Xi'an, Shaanxi, People's Republic of China.
authors.forename: Bin
authors.initials: B
authors.lastname: Lu
authors.forename: Xijing
authors.initials: X
authors.lastname: He
authors.forename: Chen-guang
authors.initials: CG
authors.lastname: Zhao
authors.forename: Hao-Peng
authors.initials: HP
authors.lastname: Li
authors.forename: Dong
authors.initials: D
authors.lastname: Wang
mesh_terms: D015502:Absorptiometry, Photon; D000328:Adult; D001268:Atlanto-Axial Joint / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery; D001696:Biomechanical Phenomena; D015519:Bone Density; D002102:Cadaver; D002574:Cervical Vertebrae / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D009809:Odontoid Process / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery; D016059:Range of Motion, Articular; D012399:Rotation