title: Examination of cervical spine kinematics in complex, multiplanar motions after anterior cervical discectomy and fusion and total disc replacement.
abstract: BACKGROUND
  The biomechanical behavior of total disc replacement (TDR) and anterior cervical discectomy and fusion (ACDF) incomplex multiplanar motion is incompletely understood. The purpose of this study was to determine whether ACDF or TDR significantly affects in vitro kinematics through a range of complex, multiplanar motions.
  
  
  METHODS
  Seven human cervical spines from C4-7 were used for this study. Intact cervical motion segments with and without implanted TDR and ACDF were tested by use of unconstrained pure bending moment testing fixtures in 7 mechanical modes: axial rotation (AR); flexion/extension (FE); lateral bending (LB); combined FE and LB; combined FE and AR; combined LB and AR; and combined FE, LB, and AR. Statistical testing was performed to determine whether differences existed in range of motion (ROM) and stiffness among spinal segments and treatment groups for each mechanical test mode.
  
  
  RESULTS
  ACDF specimens showed increased stiffness compared with the intact and TDR specimens (P < .001); stiffness was not found to be different between TDR and intact specimens. ACDF specimens showed decreased ROM in all directions compared with TDR and intact specimens at the treated level. For the coupled motion test, including AR, LB, and FE, the cranial adjacent level (C4/C5) for the intact specimens (2.7°) showed significantly less motion compared with both the TDR (6.1°, P = .009) and ACDF (6.8°, P = .002) treatment groups about the LB axis. Testing of the C4/C5 and C6/C7 levels in all other test modes yielded no significant differences in ROM comparisons, although a trend toward increasing ROM in adjacent levels in ACDF specimens compared with intact and TDR specimens was observed.
  
  
  CONCLUSIONS
  This study compared multiplanar motion under load-displacement testing of subaxial cervical motion segments with and without implanted TDR and ACDF. We found a trend toward increased motion in adjacent levels in ACDF specimens compared with TDR specimens. Biomechanical multiplanar motion testing will be useful in the ongoing development and evaluation of spinal motion-preserving implants.
authors.affiliation: Department of Orthopaedics, Warren Alpert Medical School, Brown University, Providence, RI.
authors.forename: Alan H
authors.initials: AH
authors.lastname: Daniels
authors.affiliation: Department of Orthopaedics, Warren Alpert Medical School, Brown University, Providence, RI.
authors.forename: David J
authors.initials: DJ
authors.lastname: Paller
authors.affiliation: Department of Orthopaedics, Warren Alpert Medical School, Brown University, Providence, RI.
authors.forename: Ross J
authors.initials: RJ
authors.lastname: Feller
authors.affiliation: Department of Orthopaedics, Warren Alpert Medical School, Brown University, Providence, RI.
authors.forename: Nikhil A
authors.initials: NA
authors.lastname: Thakur
authors.affiliation: Department of Orthopaedics, Warren Alpert Medical School, Brown University, Providence, RI.
authors.forename: Alison M
authors.initials: AM
authors.lastname: Biercevicz
authors.affiliation: Department of Orthopaedics, Warren Alpert Medical School, Brown University, Providence, RI.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Palumbo
authors.affiliation: Department of Orthopaedics, Warren Alpert Medical School, Brown University, Providence, RI.
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Crisco
authors.affiliation: Upstate Bone and Joint Center, Department of Orthopaedics, Upstate Medical University - SUNY, Syracuse, NY.
authors.forename: Ian A
authors.initials: IA
authors.lastname: Madom
keywords: Anterior cervical discectomy and fusion; Cervical spine biomechanics; Total disc replacement