title: New Radiographic Index for Occipito-Cervical Instability.
abstract: METHODS
  Retrospective study.
  
  
  OBJECTIVE
  To propose a new radiographic index for occipito-cervical instability.
  
  
  BACKGROUND
  Symptomatic atlanto-occipital instability requires the fusion of the atlanto-occipital joint. However, measurements of occipito-cervical translation using the Wiesel-Rothman technique, Power's ratio, and basion-axial interval are unreliable because the radiologic landmarks in the occipito-cervical junction lack clarity in radiography.
  
  
  METHODS
  One hundred four asymptomatic subjects were evaluated with lateral cervical radiographs in neutral, flexion and extension. They were stratified by age and included 52 young (20-29 years) and 52 middle-aged adults (50-59 years). The four radiographic reference points were posterior edge of hard palate (hard palate), posteroinferior corner of the most posterior upper molar tooth (molar), posteroinferior corner of the C1 anterior ring (posterior C1), and posteroinferior corner of the C2 vertebral body (posterior C2). The distance from posterior C1 and posterior C2 to the above anatomical landmarks was measured to calculate the range of motion (ROM) on dynamic radiographs. To determine the difference between the two age groups, unpaired t-tests were used. The statistical significance level was set at p<0.05.
  
  
  RESULTS
  The ROM was 4.8±7.3 mm between the hard palate and the posterior C1, 9.9±10.2 mm between the hard palate and the posterior C2, 1.7±7.2 mm between the molar to the posterior C1, and 10.4±12.1 mm between the molar to the posterior C2. There was no statistically significant difference for the ROM between the young- and the middle-aged groups. The intra-observer reliability for new radiographic index was good. The inter-observer reliability for the ROM measured by the hard palate was low, but was better than that by the molar.
  
  
  CONCLUSIONS
  ROM measured by the hard palate might be a useful new radiographic index in cases of occipito-cervical instability.
authors.affiliation: Department of Orthopaedic Surgery, Hallym University Sacred Heart Hospital, Hallym University College of Medicine, Anyang, Korea.
authors.forename: Moon Soo
authors.initials: MS
authors.lastname: Park
authors.affiliation: Department of Orthopaedic Surgery, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Seong-Hwan
authors.initials: SH
authors.lastname: Moon
authors.affiliation: Department of Orthopaedic Surgery, Hallym University Sacred Heart Hospital, Hallym University College of Medicine, Anyang, Korea.
authors.forename: Tae-Hwan
authors.initials: TH
authors.lastname: Kim
authors.affiliation: Department of Neurosurgery, Hallym University Sacred Heart Hospital, Hallym University College of Medical, Anyang, Korea.
authors.forename: Jae Keun
authors.initials: JK
authors.lastname: Oh
authors.affiliation: Department of Orthopaedic Surgery, Hallym University Sacred Heart Hospital, Hallym University College of Medicine, Anyang, Korea.
authors.forename: Ji Hoon
authors.initials: JH
authors.lastname: Nam
authors.affiliation: Department of Orthopaedic Surgery, Hallym University Sacred Heart Hospital, Hallym University College of Medicine, Anyang, Korea.
authors.forename: Jae Kyun
authors.initials: JK
authors.lastname: Jung
authors.affiliation: Washington University Orthopedics, BJC Institute of Health at Washington University School of Medicine, Chesterfield, MO, USA.
authors.forename: K Daniel
authors.initials: KD
authors.lastname: Riew
keywords: Occipito-cervical instability; Radiographic index; Range of motion