title: New classification system for ossification of the posterior longitudinal ligament using CT images.
abstract: BACKGROUND
  Ossification of the posterior longitudinal ligament (OPLL) is most frequently seen in the cervical spine. The types of cervical OPLL are classified into continuous, mixed, segmental, and other based on plain lateral X-ray. Computed tomography (CT) imaging is often used in clinical practice for evaluating ossified lesions as it can detect their precise location, size, and shape. However, to date, no CT classification of OPLL lesions has been proposed.
  
  
  METHODS
  One hundred and forty-four patients diagnosed with cervical OPLL by plain radiograph were included in this study. Sagittal and axial CT images of the cervical spine were obtained. We propose three classification systems: A, B, and axial. Classification A comprises two lesion types: bridge and nonbridge. Classification B requires examiners to describe all vertebral and intervertebral levels where OPLL exits in the cervical spine. Axial classification comprises central and lateral lesions identified on axial CT images. Seven observers evaluated CT images using this classification system, and intra- and interrater reliability were examined.
  
  
  RESULTS
  Averaged Fleiss' kappa coefficient of interrater agreement was 0.43 ± 0.26 among the seven observers, averaged intrarater reliability for the existence of OPLL was 72.4 ± 8.8% [95% confidence interval (CI) 67.5-76.8]. Fifty-four patients (37.5%) had the bridge type and 90 the nonbridge type according to Classification A; 102 (70.8%) had central and 42 (29.2%) lateral OPLL in the axial classification. Four representative cases defined according to the three classification types are reported here.
  
  
  CONCLUSIONS
  Subcommittee members of the Investigation Committee on the Ossification of the Spinal Ligaments of the Japanese Ministry of Public Health and Welfare propose three new classification systems of cervical OPLL based on CT imaging: A, B, and axial.
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, University of Toyama, 2630 Sugitani, Toyama, Toyama, 930-0194, Japan, zenji@med.u-toyama.ac.jp.
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Kawaguchi
authors.forename: Morio
authors.initials: M
authors.lastname: Matsumoto
authors.forename: Motoki
authors.initials: M
authors.lastname: Iwasaki
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Izumi
authors.forename: Atsushi
authors.initials: A
authors.lastname: Okawa
authors.forename: Shunji
authors.initials: S
authors.lastname: Matsunaga
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Chiba
authors.forename: Takashi
authors.initials: T
authors.lastname: Tsuji
authors.forename: Masashi
authors.initials: M
authors.lastname: Yamazaki
authors.forename: Takahito
authors.initials: T
authors.lastname: Fujimori
authors.forename: Toshitaka
authors.initials: T
authors.lastname: Yoshii
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Toyama
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017887:Ossification of Posterior Longitudinal Ligament / Q000145:classification* / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed