title: Investigation of ossification in the posterior longitudinal ligament using micro-focus X-ray CT scanning and histological examination.
abstract: BACKGROUND
  Ossification in the posterior longitudinal ligament (PLL) correlates with changes of enthesis during the early stages of development, but this issue remains controversial, as little is known regarding the details of this process. The aim of the present study was to elucidate part of the ossification mechanism. Thus, in the present study, we observed and evaluated minute ossifications in the PLL that did not exhibit symptoms of ossification of the posterior longitudinal ligament (OPLL).
  
  
  METHODS
  The subjects in the present study were derived from serial autopsy cases from January 2009 to December 2013 at Toho University Omori Medical Center, Japan. Minute ossifications in the PLL from autopsy subjects without any history of OPLL were screened as high-density areas using micro-focus X-ray CT, and the foci were histologically examined. Subsequently, we conducted both micro-focus X-ray CT image analysis and histological examination, and evaluated the correlation between these findings and putative predictive factors reported in previous studies.
  
  
  RESULTS
  A total of 103 individuals among the 267 subjects involved in the present study were analyzed within the study period. There were no cases involving OPLL identification prior to death, and no subjects presented with neurological symptoms of myelopathy. The incidence of cases involving high-density areas greater than 0.1 mm(2) in the PLL was 46.6 %, half of which revealed mature bone structures inside this area. Thus, the high-density areas comprised three types: a continuous posterior-annular fibrosus type (23 cases), an isolated posterior-annular fibrosus type (11 cases), and a posterior-vertebral type (29 cases). However, a positive correlation was observed between the proportion of high-density areas, age (Pearson r = 0.265, p < 0.01), and HbA1c (Pearson r = 0.294, p < 0.01). Histological examination confirmed that these high-density areas involved calcification with or without mature bone formation.
  
  
  CONCLUSIONS
  We evaluated minute foci of calcification with and without ossification in the PLL from 103 cadavers, generating the following observations: 1. Minute calcification foci greater than 0.1 mm(2) were observed in the PLL of 48 cases (46.6 %), half of which revealed mature bone structures inside this area (23.3 %). 2. The proportion of minute calcification foci observed in the present study was correlated with age and glucose tolerance, suggesting changes in the OPLL in the early stage. 3. Three different mechanisms of ossification were suggested: The two structures developed behind the disc might reflect the elongation of enthesis or rupture of annular fibrosus, while the remaining structure developed behind the vertebral body might reflect a dystrophic calcification-based bony metaplasia sequence.
authors.affiliation: Department of Orthopedic Surgery, Toho University Omori Medical Center, 6-11-1, Omori-Nishi, Ota-Ku, Tokyo, 143-8541, Japan. katsunori.fukutake@med.toho-u.ac.jp.
authors.forename: Katsunori
authors.initials: K
authors.lastname: Fukutake
authors.affiliation: Department of Surgical Pathology, Toho University School of Medicine, 6-11-1, Omori-Nishi, Ota-Ku, Tokyo, 143-8541, Japan. t-ishiwatari@med.toho-u.ac.jp.
authors.forename: Takao
authors.initials: T
authors.lastname: Ishiwatari
authors.affiliation: Department of Orthopedic Surgery, Toho University Omori Medical Center, 6-11-1, Omori-Nishi, Ota-Ku, Tokyo, 143-8541, Japan. drkan@med.toho-u.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takahashi
authors.affiliation: Department of Orthopedic Surgery, Toho University Omori Medical Center, 6-11-1, Omori-Nishi, Ota-Ku, Tokyo, 143-8541, Japan. kt11@med.toho-u.ac.jp.
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Tsuchiya
authors.affiliation: Department of Surgical Pathology, Toho University School of Medicine, 6-11-1, Omori-Nishi, Ota-Ku, Tokyo, 143-8541, Japan. yoichiro0207@med.toho-u.ac.jp.
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Okubo
authors.affiliation: Department of Surgical Pathology, Toho University School of Medicine, 6-11-1, Omori-Nishi, Ota-Ku, Tokyo, 143-8541, Japan. ushino@med.toho-u.ac.jp.
authors.forename: Minoru
authors.initials: M
authors.lastname: Shinozaki
authors.affiliation: Department of Surgical Pathology, Toho University School of Medicine, 6-11-1, Omori-Nishi, Ota-Ku, Tokyo, 143-8541, Japan. naobumi.tochigi@med.toho-u.ac.jp.
authors.forename: Naobumi
authors.initials: N
authors.lastname: Tochigi
authors.affiliation: Department of Surgical Pathology, Toho University School of Medicine, 6-11-1, Omori-Nishi, Ota-Ku, Tokyo, 143-8541, Japan. megumi.wakayama@med.toho-u.ac.jp.
authors.forename: Megumi
authors.initials: M
authors.lastname: Wakayama
authors.affiliation: Department of Surgical Pathology, Toho University School of Medicine, 6-11-1, Omori-Nishi, Ota-Ku, Tokyo, 143-8541, Japan. tetsuo.nemoto@med.toho-u.ac.jp.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Nemoto
authors.affiliation: Department of Surgical Pathology, Toho University School of Medicine, 6-11-1, Omori-Nishi, Ota-Ku, Tokyo, 143-8541, Japan. kaz@med.toho-u.ac.jp.|Department of Dermatology, Peking University First Hospital, Beijing, China. kaz@med.toho-u.ac.jp.
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Shibuya
authors.affiliation: Department of Orthopedic Surgery, Toho University Omori Medical Center, 6-11-1, Omori-Nishi, Ota-Ku, Tokyo, 143-8541, Japan. nyagira@med.toho-u.ac.jp.
authors.forename: Akihito
authors.initials: A
authors.lastname: Wada
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging* / Q000473:pathology; D005260:Female; D006801:Humans; D008297:Male; D008679:Metaplasia / Q000175:diagnosis / Q000473:pathology*; D008875:Middle Aged; D017887:Ossification of Posterior Longitudinal Ligament / Q000000981:diagnostic imaging* / Q000473:pathology*; D014057:Tomography, X-Ray Computed / Q000379:methods