title: Three-dimensional measurement of growth of ossification of the posterior longitudinal ligament.
abstract: OBJECTIVE
  Ossification of the posterior longitudinal ligament (OPLL) is a progressive disease that causes cervical myelopathy. Because 2D evaluation of ossification growth with plain lateral radiographs has limitations, the authors developed a unique technique to measure ossification progression and volume increase by using multidetector CT scanning.
  
  
  METHODS
  The authors used serial thin-slice volume data obtained by multidetector CT scanning in 5 patients. The mean patient age was 63 years, and the mean follow-up duration was 3.1 years. First, a 3D model of OPLL was semiautomatically segmented at a specific threshold. Then, a preoperative model of OPLL was superimposed on a postoperative model using voxel-based registration of the vertebral bodies. Progression and volume increase were measured using a digital viewer that was developed by the authors. Progression was visualized using a color-coded contour on the surface of the OPLL model.
  
  
  RESULTS
  All patients had progression of 0.5 mm or greater. The mean values concerning OPLL growth were as follows: maximum progression length, 4.7 mm; progression rate, 1.5 mm/year; volume increase, 1622 mm(3); volume expansion rate, 37%; and volume increase rate, 484 mm(3)/year. The accuracy of superimposition by voxel-based registration, defined as closeness to the true value, was less than 0.31 mm. For intraobserver reproducibility of the volume measurement, the mean intraclass correlation coefficient, root mean square error, and coefficient of variation were 0.987, 16.0 mm(3), and 1.7%, respectively.
  
  
  CONCLUSIONS
  Ossification of the posterior longitudinal ligament progresses even after surgery. Three-dimensional evaluation with the aid of CT scans is a useful and reliable method for assessing that growth.
authors.affiliation: Department of Orthopedic Surgery, Osaka University Graduate School of Medicine, Suita, Osaka, Japan.
authors.forename: Takahito
authors.initials: T
authors.lastname: Fujimori
authors.forename: Motoki
authors.initials: M
authors.lastname: Iwasaki
authors.forename: Yukitaka
authors.initials: Y
authors.lastname: Nagamoto
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ishii
authors.forename: Hironobu
authors.initials: H
authors.lastname: Sakaura
authors.forename: Masafumi
authors.initials: M
authors.lastname: Kashii
authors.forename: Hideki
authors.initials: H
authors.lastname: Yoshikawa
authors.forename: Kazuomi
authors.initials: K
authors.lastname: Sugamoto
mesh_terms: D000328:Adult; D000368:Aged; D018450:Disease Progression; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D017887:Ossification of Posterior Longitudinal Ligament / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D020127:Recovery of Function; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed / Q000379:methods*