title: Analysis of pelvic incidence from 3-dimensional images of a normal population.
abstract: METHODS
  Pelvic incidence (PI) was measured in 3 dimensions from computed tomographic (CT) images of normal subjects using a computerized method.
  
  
  OBJECTIVE
  To obtain the angle of PI from 3-dimensional (3D) images and analyze its distribution in a normal population.
  
  
  BACKGROUND
  The sagittal alignment of the pelvis is usually evaluated in 2-dimensional (2D) sagittal radiographs. The purpose of this study is to measure and analyze PI, which represents a key parameter of sagittal alignment, in 3D images.
  
  
  METHODS
  A computerized method, based on image-processing techniques, was used to automatically determine the anatomical references required to measure PI, that is, the centers of the femoral heads in 3 dimensions and the center and inclination of the sacral end plate in 3 dimensions. Multiplanar image reformation was applied to obtain perfect sagittal views with all anatomical structures completely in line with the hip axis from which PI was calculated.
  
  
  RESULTS
  PI was successfully obtained in CT images of 370 normal subjects (mean age: 41.5 years; range: 1-87 years). The mean PI (± standard deviation) was equal to 46.6° (±9.2°) for male subjects, 47.6° (±10.7°) for female subjects, and 47.1° (±10.0°) for both sexes. No statistically significant differences were obtained between the sexes, and statistically significant correlation was obtained between PI and age.
  
  
  CONCLUSIONS
  In this study, the sagittal alignment of the pelvis was evaluated in terms of PI completely in 3 dimensions. The results show that computerized measurements of PI in 3 dimensions are less variable than manual measurements. The large span of PI values for normal subjects indicates that the natural variation of PI is relatively large.
authors.affiliation: Laboratory of Imaging Technologies, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia. tomaz.vrtovec@fe.uni-lj.si
authors.forename: Tomaž
authors.initials: T
authors.lastname: Vrtovec
authors.forename: Michiel M A
authors.initials: MM
authors.lastname: Janssen
authors.forename: Franjo
authors.initials: F
authors.lastname: Pernuš
authors.forename: René M
authors.initials: RM
authors.lastname: Castelein
authors.forename: Max A
authors.initials: MA
authors.lastname: Viergever
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007223:Infant; D008297:Male; D008875:Middle Aged; D010388:Pelvis / Q000000981:diagnostic imaging*; D011859:Radiography; D012016:Reference Values; D012447:Sacrum / Q000000981:diagnostic imaging*