title: Characteristics of ossification of the spinal ligament; incidence of ossification of the ligamentum flavum in patients with cervical ossification of the posterior longitudinal ligament - Analysis of the whole spine using multidetector CT.
abstract: BACKGROUND
  Ossification of the posterior longitudinal ligament (OPLL) and ossification of the ligamentum flavum (OLF) are characterized by replacement of ligamentous tissue by ectopic new bone formation. Although the background of both diseases might be similar, there are some differences between two diseases. Some patients have both OPLL and OLF. However, the incidence of both OPLL and OLF is still unclear and the precise lesions have not been investigated, yet. This study was conducted to evaluate OLF of the whole spine in patients with cervical OPLL and to analyze the relationship of the ossified lesions between OLF and OPLL.
  
  
  METHODS
  One hundred seventy eight patients who were diagnosed as cervical OPLL by plain radiographs were included. CT images of the whole spine were taken. Ossified lesions were checked at each level of vertebral body and intervertebral disc. The ossification index of OPLL (OPLL OS index) was determined by the sum of the levels of vertebral bodies and intervertebral discs where OPLL existed. The same index was applied for detecting the level of OLF (OLF OS index). Age, gender and OPLL characteristics were compared between the OLF(+) group, OLF was seen at any levels of the spinal canal, and the OLF(-) group, OLF was not seen.
  
  
  RESULTS
  The most frequent level of OPLL was at C5 vertebral level and OLF was predominant at upper and lower thoracic levels. Seventeen patients (9.6%) had OPLL and OLF at the same spinal level. The averaged OPLL OS index of the total spine in these patients was 8.7 ± 6.1, ranged from 1 to 36. The averaged OLF OS index of the total spine was 3.1 ± 2.2 (ranged from 1 to 13) in the patients who had OLF at any levels of the whole spine. One hundred fifteen patients (64.6%) with cervical OPLL had OLF at any levels of the whole spine. No relationship was found between the OPLL OS index and the OLF OS index. There was no significant difference among the data between the OLF(+) group and the OLF(-) group.
  
  
  CONCLUSIONS
  This study demonstrated 64.6% of the patients with cervical OPLL had OLF, mainly in the thoracic spine. However, there was no relationship regarding the severity of the ossified lesions between OPLL and OLF. CT analysis of the whole spine should be carried out for the early detection of OPLL and OLF in patients with cervical OPLL.
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, University of Toyama, Toyama, Japan. Electronic address: zenji@med.u-toyama.ac.jp.
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Kawaguchi
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, University of Toyama, Toyama, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Nakano
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, University of Toyama, Toyama, Japan.
authors.forename: Taketoshi
authors.initials: T
authors.lastname: Yasuda
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, University of Toyama, Toyama, Japan.
authors.forename: Shoji
authors.initials: S
authors.lastname: Seki
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, University of Toyama, Toyama, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Hori
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, University of Toyama, Toyama, Japan.
authors.forename: Kayo
authors.initials: K
authors.lastname: Suzuki
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, University of Toyama, Toyama, Japan.
authors.forename: Hiroto
authors.initials: H
authors.lastname: Makino
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, University of Toyama, Toyama, Japan.
authors.forename: Tomoatsu
authors.initials: T
authors.lastname: Kimura
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002574:Cervical Vertebrae; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D017843:Ligamentum Flavum / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D061330:Multidetector Computed Tomography; D015588:Observer Variation; D017887:Ossification of Posterior Longitudinal Ligament / Q000150:complications*; D013904:Thoracic Vertebrae