title: The rotation ratios method: a method to describe altered pelvic orientation in sequential radiographs.
abstract: BACKGROUND
  A method to describe pelvic rotations between pairs of standard sequential pelvic anteroposterior radiographs based on a pelvic phantom is described in a former study.
  
  
  OBJECTIVE
  To expand this method into clinical use based on clinical data.
  
  
  METHODS
  Teardrop distances were measured on 262 pelvic radiographs from 46 patients in a clinical material using a computer program designed to perform measurements on digital radiographs. Anthropometric data recorded from 141 pelvises in an anatomical collection were employed in a computer program designed to simulate radiographs of virtual objects. Virtual rotations of the pelvises were carried out with 4653 virtual radiographs obtained. Virtual radiographic measures were analyzed.
  
  
  RESULTS
  A statistically significant difference of 8 mm between mean teardrop distance in females (120 mm) and males (112 mm) was found in the clinical material. A set of formulas describing the relations between differences of two rotation ratios and pelvic rotations were derived. Four simple regression analyses were carried out with the use of virtual measures. Adjusted teardrop distances were implemented.
  
  
  CONCLUSIONS
  A clinical method to describe pelvic rotations using standard pelvic radiographs was developed.
authors.affiliation: Norwegian Orthopedic Implant Research Unit, and Department of Radiology, St. Olav's Hospital, Trondheim University Hospital, Trondheim, Norway.
authors.forename: O A
authors.initials: OA
authors.lastname: Foss
authors.forename: J
authors.initials: J
authors.lastname: Klaksvik
authors.forename: P
authors.initials: P
authors.lastname: Benum
authors.forename: S
authors.initials: S
authors.lastname: Anda
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D010384:Pelvic Bones / Q000000981:diagnostic imaging*; D019047:Phantoms, Imaging; D011859:Radiography; D012044:Regression Analysis; D015203:Reproducibility of Results; D012399:Rotation