title: Facet joint contact pressure is not significantly affected by ProDisc cervical disc arthroplasty in sagittal bending: a single-level cadaveric study.
abstract: BACKGROUND
  Total disc arthroplasty is a motion-preserving spinal procedure that has been investigated for its impact on spinal motions and adjacent-level degeneration. However, the effects of disc arthroplasty on facet joint biomechanics remain undefined despite the critical role of these posterior elements on guiding and limiting spinal motion.
  
  
  OBJECTIVE
  The goal was to measure the pressure in the facet joint in cadaveric human cervical spines subjected to sagittal bending before and after implantation of the ProDisc-C (Synthes Spine Company, L.P, West Chester, PA, USA).
  
  
  METHODS
  A biomechanical study was performed using cadaveric human cervical spines during sagittal bending in the intact and implanted conditions.
  
  
  METHODS
  Seven C2-T1 osteoligamentous cadaveric cervical spines were instrumented with a transducer to measure the C5-C6 facet pressure profiles during physiological sagittal bending, before and after implantation of a ProDisc-C at that level. Rotations of the index segment and global cervical spine were also quantified.
  
  
  RESULTS
  The mean C5-C6 range of motion significantly increased (p=.009) from 9.6°±5.1° in the intact condition to 16.2°±3.6° after implantation. However, despite such changes in rotation, there was no significant difference in the facet contact pressure during extension between the intact (64±30 kPa) and implanted (44±55 kPa) conditions. Similarly, there was no difference in facet pressure developed during flexion.
  
  
  CONCLUSIONS
  Although implantation of a ProDisc-C arthroplasty device at the C5-C6 level increases angular rotations, it does not significantly alter the local facet pressure at the index level in flexion or extension. Using a technique that preserves the capsular ligament, this study provides the first direct measurement of cervical facet pressure in a disc arthroplasty condition.
authors.affiliation: Department of Neurosurgery, 3 Silverstein Hospital of the University of Pennsylvania, 3400 Spruce St., Philadelphia, PA 19104, USA.
authors.forename: Joel A
authors.initials: JA
authors.lastname: Bauman
authors.forename: Nicolas V
authors.initials: NV
authors.lastname: Jaumard
authors.forename: Benjamin B
authors.initials: BB
authors.lastname: Guarino
authors.forename: Christine L
authors.initials: CL
authors.lastname: Weisshaar
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Lipschutz
authors.forename: William C
authors.initials: WC
authors.lastname: Welch
authors.forename: Beth A
authors.initials: BA
authors.lastname: Winkelstein
mesh_terms: D001178:Arthroplasty / Q000379:methods*; D001696:Biomechanical Phenomena; D002102:Cadaver; D002574:Cervical Vertebrae / Q000502:physiology*; D006801:Humans; D007403:Intervertebral Disc / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009038:Motion; D011312:Pressure; D016059:Range of Motion, Articular; D012399:Rotation; D013314:Stress, Mechanical; D014160:Transducers, Pressure; D021801:Zygapophyseal Joint / Q000502:physiology*