title: New radiological parameters for the assessment of atlantoaxial instability in children with Down syndrome: the normal values and the risk of spinal cord injury.
abstract: OBJECTIVE
  To determine the normal values and usefulness of the C1/4 space available for spinal cord (SAC) ratio and C1 inclination angle, which are new radiological parameters for assessing atlantoaxial instability in children with Down syndrome.
  
  
  METHODS
  We recruited 272 children with Down syndrome (including 14 who underwent surgical treatment), and 141 children in the control group. All were aged between two and 11 years. The C1/4 SAC ratio, C1 inclination angle, atlas-dens interval (ADI), and SAC were measured in those with Down syndrome, and the C1/4 SAC ratio and C1 inclination angle were measured in the control group.
  
  
  RESULTS
  The mean C1/4 SAC ratio in those requiring surgery with Down syndrome, those with Down syndrome not requiring surgery and controls were 0.63 (standard deviation (sd) 0.1), 1.15 (sd 0.13) and 1.29 (sd 0.14), respectively, and the mean C1 inclination angles were -3.1° (sd 10.7°), 15.8° (sd 7.3) and 17.2° (sd 7.3), in these three groups, respectively. The mean ADI and SAC in those with Down syndrome requiring surgery and those with Down syndrome not requiring surgery were 9.8 mm (sd 2.8) and 4.3 mm (sd 1.0), and 11.1 mm (sd 2.6) and 18.5 mm (sd 2.4), respectively.
  
  
  CONCLUSIONS
  The normal values of the C1/4 SAC ratio and the C1 inclination angle were found to be about 1.2° and 15º, respectively. Cite this article: Bone Joint J 2016;98-B:1704-10.
authors.affiliation: Kanagawa Children's Medical Center, 2-138-4 Mutsukawa, Minami-ku, Yokohama city, Kanagawa, 232-8555, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Nakamura
authors.affiliation: Yokohama City University, 3-9 Fukuura, Kanazawa-ku, Yokohama city, Kanagawa, 236-0004, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Inaba
authors.affiliation: Yokohama Brain and Spine Center, 1-2-1 Takigashira, Isogo-ku, Yokohama city, Kanagawa, 235-0012, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Aota
authors.affiliation: Saiseikai Wakakusa Hospital, 12-1 Hiragatacho, Kanazawa-ku, Yokohama city, Kanagawa, 236-8653, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Oba
authors.affiliation: Kanagawa Children's Medical Center, 2-138-4 Mutsukawa, Minami-ku, Yokohama city, Kanagawa, 232-8555, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Machida
authors.affiliation: Kanagawa Children's Medical Center, 2-138-4 Mutsukawa, Minami-ku, Yokohama city, Kanagawa, 232-8555, Japan.
authors.lastname: N Aida
authors.affiliation: Kanagawa Children's Medical Center, 2-138-4 Mutsukawa, Minami-ku, Yokohama city, Kanagawa, 232-8555, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kurosawa
authors.affiliation: Yokohama City University, 3-9 Fukuura, Kanazawa-ku, Yokohama city, Kanagawa, 236-0004, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Saito
mesh_terms: D017677:Age Distribution; D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D016022:Case-Control Studies; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology; D002648:Child; D002675:Child, Preschool; D004314:Down Syndrome / Q000150:complications* / Q000473:pathology; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging* / Q000209:etiology / Q000473:pathology / Q000601:surgery; D008297:Male; D011859:Radiography; D012016:Reference Values; D017678:Sex Distribution; D013119:Spinal Cord Injuries / Q000209:etiology*
keywords: Atlantoaxial instability; C1 inclination angle; C1/4 SAC ratio; Children; Down syndrome; Space available for spinal cord