title: The intermetatarsal and metatarsal declination angles: geometry as a source of error.
abstract: BACKGROUND
  The measurements on radiographs of the foot are believed to give an objective impression of foot deformities. In patient management, the outcome of these measurements is one of the factors that the physician takes into consideration. In fact, the radiograph is a projection of three-dimensional structures and is as such liable to a certain amount of distortion. To our knowledge this distortion has not been quantified, although it seems important for the interpretation of the measurements.
  
  
  METHODS
  First, mathematical models based on the geometry of standard anteroposterior and lateral radiographs were constructed and analyzed. Then, we simulated radiography with these models on three-dimensional data of metatarsals originating from CT scans of 10 normal volunteers.
  
  
  RESULTS
  The distortion of the declination angles of the metatarsals was practically negligible. The intermetatarsal angles were distorted up to 5.4 degrees. The measured angles underestimated the three-dimensional angles.
  
  
  CONCLUSIONS
  In interpreting the measurements of the metatarsal declination angles, distortion was not a factor. For intermetatarsal angles variability of distortion was only about one third of the reported interobserver variability, but it may have cumulative effects on the error of measured intermetatarsal angles. Moreover, the theoretical models predicted larger distortions in patients with deformities. In interpretation of angular measurements the physician should be aware of these pitfalls.
authors.affiliation: Department of Radiology, University Hospital Maastricht, P. Debyelaan 25, Maastricht, Limburg 6202 AZ, The Netherlands. rwe@rdia.azm.nl
authors.forename: René
authors.initials: R
authors.lastname: Weijers
authors.forename: Gerrit
authors.initials: G
authors.lastname: Kemerink
authors.forename: Henk
authors.initials: H
authors.lastname: van Mameren
authors.forename: Geert
authors.initials: G
authors.lastname: Walenkamp
authors.forename: Alphons G H
authors.initials: AG
authors.lastname: Kessels
mesh_terms: D000328:Adult; D003198:Computer Simulation; D003951:Diagnostic Errors; D005260:Female; D005545:Forefoot, Human / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008682:Metatarsal Bones / Q000000981:diagnostic imaging*; D008875:Middle Aged; D011859:Radiography