title: Kinematic analysis of the cervical cord and cervical canal by dynamic neck motion.
abstract: METHODS
  Normal cervical sagittal length patterns were measured by magnetic resonance imaging (MRI).
  
  
  OBJECTIVE
  The aim of this study was to evaluate the relationship of sagittal length patterns between the cervical cord and the cervical canal in flexion-extension kinematics.
  
  
  BACKGROUND
  Cervical dynamic factors sometimes cause a cervical spondylotic myelopathy in elderly subjects and an overstretching myelopathy in juvenile subjects. Previous studies showed the length changing of the cervical cord in flexion and extension. However, there is no detailed literature about the relationship between cervical vertebral motion and cord distortion yet.
  
  
  METHODS
  Sixty-two normal subjects (28 male and 34 female, 42.1±8.5 years old) without neck motion disturbances and abnormalities on cervical X-ray and MRI were enrolled in this study.
  
  
  RESULTS
  The cervical cord length was significantly longer in flexion and significantly shorter in extension in all cervical cord sagittal lines. The cervical canal length pattern was also the same as the cervical cord. The elongation of the cervical cord and canal was the largest at the site of the posterior cervical canal and the shortest at the anterior canal site. The positions of the cerebellar tonsils were verified at each neck position.
  
  
  CONCLUSIONS
  The posterior elements of the cervical canal were most affected by neck motion. Movement directions of the upper cervical cord were verified among the various neck positions.
authors.affiliation: Department of Orthopedic Surgery, Tokyo Medical University, Tokyo, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Endo
authors.affiliation: Department of Orthopedic Surgery, Tokyo Medical University, Tokyo, Japan.
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Suzuki
authors.affiliation: Department of Orthopedic Surgery, Tokyo Medical University, Tokyo, Japan.
authors.forename: Hirosuke
authors.initials: H
authors.lastname: Nishimura
authors.affiliation: Department of Orthopedic Surgery, Tokyo Medical University, Tokyo, Japan.
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Tanaka
authors.affiliation: Department of Orthopedic Surgery, Tokyo Medical University, Tokyo, Japan.
authors.forename: Takaaki
authors.initials: T
authors.lastname: Shishido
authors.affiliation: Department of Orthopedic Surgery, Tokyo Medical University, Tokyo, Japan.
authors.forename: Kengo
authors.initials: K
authors.lastname: Yamamoto
keywords: Biomechanics; Cervical spine; Magnetic resonance imaging