title: Biomechanics of a fixed-center of rotation cervical intervertebral disc prosthesis.
abstract: BACKGROUND
  Past in vitro experiments studying artificial discs have focused on range of motion. It is also important to understand how artificial discs affect other biomechanical parameters, especially alterations to kinematics. The purpose of this in vitro investigation was to quantify how disc replacement with a ball-and-socket disc arthroplasty device (ProDisc-C; Synthes, West Chester, Pennsylvania) alters biomechanics of the spine relative to the normal condition (positive control) and simulated fusion (negative control).
  
  
  METHODS
  Specimens were tested in multiple planes by use of pure moments under load control and again in displacement control during flexion-extension with a constant 70-N compressive follower load. Optical markers measured 3-dimensional vertebral motion, and a strain gauge array measured C4-5 facet loads.
  
  
  RESULTS
  Range of motion and lax zone after disc replacement were not significantly different from normal values except during lateral bending, whereas plating significantly reduced motion in all loading modes (P < .002). Plating but not disc replacement shifted the location of the axis of rotation anteriorly relative to the intact condition (P < 0.01). Coupled axial rotation per degree of lateral bending was 25% ± 48% greater than normal after artificial disc replacement (P = .05) but 37% ± 38% less than normal after plating (P = .002). Coupled lateral bending per degree of axial rotation was 37% ± 21% less than normal after disc replacement (P < .001) and 41% ± 36% less than normal after plating (P = .001). Facet loads did not change significantly relative to normal after anterior plating or arthroplasty, except that facet loads were decreased during flexion in both conditions (P < .03).
  
  
  CONCLUSIONS
  In all parameters studied, deviations from normal biomechanics were less substantial after artificial disc placement than after anterior plating.
authors.affiliation: Spinal Biomechanics Laboratory, Barrow Neurological Institute, Phoenix, AZ.
authors.forename: Neil R
authors.initials: NR
authors.lastname: Crawford
authors.affiliation: Spinal Biomechanics Laboratory, Barrow Neurological Institute, Phoenix, AZ.
authors.forename: Seungwon
authors.initials: S
authors.lastname: Baek
authors.affiliation: Spinal Biomechanics Laboratory, Barrow Neurological Institute, Phoenix, AZ.
authors.forename: Anna G U
authors.initials: AG
authors.lastname: Sawa
authors.affiliation: Department of Neurosurgery, College of Medicine, University of Oklahoma, Oklahoma City, OK.
authors.forename: Sam
authors.initials: S
authors.lastname: Safavi-Abbasi
authors.affiliation: Spinal Biomechanics Laboratory, Barrow Neurological Institute, Phoenix, AZ.
authors.forename: Volker K H
authors.initials: VK
authors.lastname: Sonntag
authors.affiliation: Department of Neurological Surgery, London Health Sciences Centre, London, Ontario, Canada.
authors.forename: Neil
authors.initials: N
authors.lastname: Duggal
keywords: Artificial disc; Biomechanics; Kinematics