title: The severity of basilar invagination and atlantoaxial dislocation correlates with sagittal joint inclination, coronal joint inclination, and craniocervical tilt: a description of new indexes for the craniovertebral junction.
abstract: BACKGROUND
  Joint-distraction and intra-operative manipulation surgeries to correct basilar invagination (BI) and atlantoaxial dislocation (AAD) are becoming standard procedures. However, current data are unable to aid in the understanding of normal and abnormal morphology of the C1/C2 joints.
  
  
  OBJECTIVE
  To study various aspects of C1/C2 joint morphology to create normative and patient data on joint abnormalities that could provide the surgeon with objective data for surgical planning and approach.
  
  
  METHODS
  Seventy patients (age, 15-45 years) were compared with an equal number of age- and sex-matched control subjects (age, 21.9±8.2 years) with irreducible BI and AAD from a developmental origin (May 2010-July 2013). Joint anatomy was studied with the use of thin-slice computed tomography scans. The joint parameters studied included sagittal joint inclination, craniocervical tilt, coronal joint inclination, surface area, joint overlap index, and joint reciprocity. The severity of BI and the severity of AAD were compared.
  
  
  RESULTS
  Sagittal joint inclination and craniocervical tilt significantly correlated with both BI and AAD (P<.01). Coronal joint inclination correlated with BI (P=.2). The mean sagittal joint inclination value in control subjects was 87.15±5.65° and in patients with BI and AAD was 127.1±22.05°. The mean craniocervical tilt value in controls was 60.2±9.2° and in patients with BI and AAD was 84.0±15.1°. The mean coronal joint inclination value in control subjects was 110.3±4.23° and in patients with BI and AAD was 121.15±14.6°.
  
  
  CONCLUSIONS
  This study has demonstrated for the first time the important role of joint orientation and its correlation with the severity of BI and AAD and has described new joint indexes.
authors.affiliation: Department of Neurosurgery and Neuroradiology, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: P Sarat
authors.initials: PS
authors.lastname: Chandra
authors.forename: Nishant
authors.initials: N
authors.lastname: Goyal
authors.forename: Avnish
authors.initials: A
authors.lastname: Chauhan
authors.forename: Abuzer
authors.initials: A
authors.lastname: Ansari
authors.forename: Bhawani Shankar
authors.initials: BS
authors.lastname: Sharma
authors.forename: Ajay
authors.initials: A
authors.lastname: Garg
mesh_terms: D000293:Adolescent; D000328:Adult; D001268:Atlanto-Axial Joint / Q000002:abnormalities* / Q000601:surgery; D005260:Female; D006801:Humans; D004204:Joint Dislocations / Q000473:pathology; D008297:Male; D008875:Middle Aged; D010985:Platybasia / Q000473:pathology / Q000601:surgery; D014057:Tomography, X-Ray Computed; D055815:Young Adult