title: Three-dimensional assessment of the intervertebral kinematics after Mobi-C total disc replacement at the cervical spine in vivo using the EOS stereoradiography system.
abstract: BACKGROUND
  Because 3-dimensional computed tomography and magnetic resonance imaging analysis of the spinal architecture is done with the patient in the supine position, stereoradiography may be more clinically relevant for the measurement of the relative displacements of the cervical vertebrae in vivo in the upright position. The innovative EOS stereoradiography system was used for measuring the relative angular displacements of the cervical vertebrae in a limited population to determine its feasibility. The precision and accuracy of the method were investigated.
  
  
  METHODS
  In 9 patients with 16 Mobi-C prostheses (LDR Medical, Troyes, France) and 12 healthy subjects, EOS stereoradiography of the lower cervical spine (C3-7) was performed in the neutral upright position of the neck, flexion, extension, left and right lateral bending, and left and right axial rotation. The angular displacements were measured from the neutral position to every other posture. The random error was studied in terms of reproducibility. In addition, an in vitro protocol was performed in 6 specimens to investigate accuracy.
  
  
  RESULTS
  The reproducibility and the accuracy variables varied similarly between 1.2° and 3.2° depending on the axis and direction of rotation under consideration. The Mobi-C group showed less mobility than the control group, whereas the pattern of coupling was similar.
  
  
  CONCLUSIONS
  Overall, the feasibility of dynamic EOS stereoradiography was shown. The prosthesis replicates the pattern of motion of the normal cervical spine.
authors: Biomechanics Lab, Arts et Métiers ParisTech, Centre national de la recherche scientifique (CNRS), unités mixtes de recherche (UMR) 8005, Paris, France ; Department of Orthopaedic Surgery, Hôpital Pitié Salpétrière Assistance Publique - Hôpitaux de Paris (AP-HP), Paris, France.
authors: Marc-Antoine
authors: MA
authors: Rousseau
authors: Biomechanics Lab, Arts et Métiers ParisTech, Centre national de la recherche scientifique (CNRS), unités mixtes de recherche (UMR) 8005, Paris, France.
authors: Sébastien
authors: S
authors: Laporte
authors: Department of Neurosurgery, Hôpital La Source, Orléans, France.
authors: Thierry
authors: T
authors: Dufour
authors: Department of Orthopaedic Surgery, Hopitaux Universitaires de Strasbourg, Strasbourg, France.
authors: Jean-Paul
authors: JP
authors: Steib
authors: Department of Orthopaedic Surgery, Hôpital Pitié Salpétrière Assistance Publique - Hôpitaux de Paris (AP-HP), Paris, France.
authors: Jean-Yves
authors: JY
authors: Lazennec
authors: Biomechanics Lab, Arts et Métiers ParisTech, Centre national de la recherche scientifique (CNRS), unités mixtes de recherche (UMR) 8005, Paris, France.
authors: Wafa
authors: W
authors: Skalli
keywords: Cervical spine; Disc prosthesis; EOS system; In vivo; Kinematics; Stereoradiography