title: Biomechanical evaluation of the Total Atlanto-odontoid Joint Arthroplasty System: an in vitro human cadaveric study.
abstract: BACKGROUND
  Atlanto-odontoid joint arthroplasty is a motion restoring procedure suggested as an alternative to rigid fixation after surgical decompression. The purpose of this study was to evaluate the kinematics and pullout strength of a novel Total Atlanto-odontoid Joint Arthroplasty System using human cadaveric specimens.
  
  
  METHODS
  Nondestructive biomechanical tests were performed on 24 fresh craniocervical specimens separated into two groups: 1) the prosthesis implantation group and 2) Harms transoral atlantoaxial plate fixation group. The following configurations were investigated: intact, after decompression, and instrumented. Range of motion and neutral zone were calculated for the C1-C2 segment. In a second experimental series, 8 sets of fresh atlantoaxial specimens were used to test the pullout strength of the atlas-axis components.
  
  
  RESULTS
  Compared with Harms rigid fixation, the Total Atlanto-odontoid Joint Arthroplasty System significantly increased the range of motion and neutral zone in all directions (P<.001). In addition, compared with the intact state, the only significant change in the range of motion and neutral zone with the Total Atlanto-odontoid Joint Arthroplasty System implantation was an increase in lateral bending (P<.001). The pullout strength created by the anterior C2 transpedicular screw was greater than that of the C2 vertebral screw and C1 lateral mass screw (P<.001), and the C1 lateral mass screw was stiffer than the C2 vertebral screw (P=.02).
  
  
  CONCLUSIONS
  Biomechanical analyses suggest that the Total Atlanto-odontoid Joint Arthroplasty System was able to provide reliable fixation strength and preserve the normal kinematics of the C1-C2 segment after decompressive procedures.
authors.affiliation: Department of Orthopaedic Surgery, Second Affiliated Hospital of Medical School of Xi'an Jiaotong University, Xi'an, Shaanxi, People's Republic of China.
authors.forename: Xuan
authors.initials: X
authors.lastname: Cai
authors.forename: Xijing
authors.initials: X
authors.lastname: He
authors.forename: Haopeng
authors.initials: H
authors.lastname: Li
authors.forename: Dong
authors.initials: D
authors.lastname: Wang
mesh_terms: D015502:Absorptiometry, Photon; D000328:Adult; D000368:Aged; D001178:Arthroplasty; D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery*; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D006801:Humans; D008297:Male; D008875:Middle Aged; D009038:Motion; D011474:Prosthesis Design; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000295:instrumentation*; D055815:Young Adult