title: In vivo evaluation of dynamic characteristics of the normal, fused, and disc replacement cervical spines.
abstract: METHODS
  In vivo human and biomechanical study.
  
  
  OBJECTIVE
  To quantify the in vivo kinematic and kinetic variations in the normal, fused, and disc replacement cervical spines.
  
  
  BACKGROUND
  Clinical and cadaveric studies have reported the motions and forces after an anterior cervical decompression and fusion (ACDF) or implantation of a cervical artificial disc replacement (CADR). However, there is no current study that describes the in vivo dynamic data of these 2 groups and compares them with that of a normal group.
  
  
  METHODS
  Ten normal subjects, 10 patients treated with an ACDF (C5-C6), and 10 patients having CADR (C5-C6) performed full flexion to extension motions under fluoroscopic surveillance. Kinematic data were obtained from the fluoroscopic images. Kinetic data were derived based on an inverse dynamic model of the entire cervical spine.
  
  
  RESULTS
  Even though the range of motion was larger for the normal group than for the ACDF group, the intersegmental rotations at the adjacent C6-C7 and C4-C5 levels in the ACDF group were 13.4 degrees and 8.8 degrees compared with 3.7 degrees and 4.8 degrees in the normal group, respectively, during the neck motion from 20 degrees flexion to 15 degrees extension. The difference at the C3-C4 level was 1 degree on average. Both the transverse contact forces and the soft tissue forces in the ACDF group were significantly larger than those in the normal group. The vertical forces in the ACDF group were smaller than those in the normal group, but there were no statistical differences. The CADR group exhibited kinematic and kinetic results similar to the normal group.
  
  
  CONCLUSIONS
  In terms of restoring the normal dynamic motion of the cervical spine, CADR may be an alternative to the ACDF.
authors.affiliation: University of Tennessee, Knoxville, TN 37996, USA. fliu3@utk.edu
authors.forename: Fei
authors.initials: F
authors.lastname: Liu
authors.forename: Joseph
authors.initials: J
authors.lastname: Cheng
authors.forename: Richard D
authors.initials: RD
authors.lastname: Komistek
authors.forename: Mohamed R
authors.initials: MR
authors.lastname: Mahfouz
authors.forename: Adrija
authors.initials: A
authors.lastname: Sharma
mesh_terms: D001187:Artificial Organs; D001696:Biomechanical Phenomena; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000502:physiology* / Q000601:surgery; D019299:Decompression, Surgical; D005471:Fluoroscopy; D019416:Head Movements / Q000502:physiology; D006801:Humans; D007403:Intervertebral Disc / Q000601:surgery*; D016059:Range of Motion, Articular; D020127:Recovery of Function; D013117:Spinal Cord Compression / Q000601:surgery; D013123:Spinal Fusion