title: How the increase of the cervical disc space height affects the facet joint: an anatomy study.
abstract: METHODS
  In vitro study on the effect of increasing the height of the cervical disc space on the facet joint.
  
  
  OBJECTIVE
  To demonstrate how facet joint articulation is affected by increasing the cervical disc space height.
  
  
  BACKGROUND
  A surgeon attempts to increase the disc space and inserts a larger artificial disc than normal in order to keep the intervertebral foramen open and the prosthesis stable. However, it is hypothesized by the current authors that this procedure could have an adverse effect on the facet joints.
  
  
  METHODS
  Computerized tomography images passing through the disc space and the center of the C4-C7 facet joints (sagittal plane) were obtained from 15 cadaveric cervical spine specimens. A 1-mm incremental increase to a total 5 mm in disc space height was performed to simulate the changes seen in disc replacement. The change in the facet joint articulation overlap and space in the sagittal plane at normal and each displacement was measured.
  
  
  RESULTS
  Each 1-mm incremental increase in disc space at C4-C5 translated to a decrease in the facet joint articulation overlap in the sagittal plane by approximately 8%. The mean facet joint space increased approximately 0.8 mm. At the C5-C6 and the C6-C7 levels, the articulation overlap decreased by approximately 7% and the facet joint space increased approximately 0.8 mm.
  
  
  CONCLUSIONS
  There is a significant decrease of the facet joint articulation overlap in the sagittal plane and an increase in the facet joint space following an increase in the cervical disc space. The inappropriate increase of the disc space height may result in facet joint subluxation and could lead to the accelerated failure of the artificial disc.
authors.affiliation: Department of Orthopaedic Surgery, Medical University of Ohio, Toledo, OH 43614, USA. jialiu@mco.edu
authors.forename: Jiayong
authors.initials: J
authors.lastname: Liu
authors.forename: Nabil A
authors.initials: NA
authors.lastname: Ebraheim
authors.forename: Steven P
authors.initials: SP
authors.lastname: Haman
authors.forename: Chris G
authors.initials: CG
authors.lastname: Sanford
authors.forename: Koichi
authors.initials: K
authors.lastname: Sairyo
authors.forename: Ahmad
authors.initials: A
authors.lastname: Faizan
authors.forename: Lee
authors.initials: L
authors.lastname: Woldenberg
authors.forename: Vijay K
authors.initials: VK
authors.lastname: Goel
mesh_terms: D002102:Cadaver; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging* / Q000601:surgery*; D004867:Equipment Design; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007403:Intervertebral Disc / Q000000981:diagnostic imaging* / Q000601:surgery*; D019736:Prostheses and Implants; D014057:Tomography, X-Ray Computed