title: Measurement of joint space width in hip osteoarthritis: influence of joint positioning and radiographic procedure.
abstract: OBJECTIVE
  We assessed the influence of patient positioning and radiographic procedure, and defined a smallest detectable difference (SDD) in hip osteoarthritis (OA).
  
  
  METHODS
  OA hip patients each had a standardized pelvic radiograph and, 5 min later, a modified pelvic radiograph with the feet internally rotated 5 degrees (part 1 of the study), the X-ray beam centred on the umbilicus (part 2), or another standardized pelvic radiograph (part 3).
  
  
  RESULTS
  Corresponding mean differences in joint space width (JSW) measurements (limits of agreement) between views were +0.03 (-0.53 to +0.59), -0.31 (-1.15 to +0.53) and -0.02 (-0.48 to +0.44) mm. The two views differed significantly in mean JSW in part 2 of the study (P=1.6x10(-4)), but not in part 1 (P=0.375) and part 3 (P=0.580). The SDD estimate was 0.46 mm.
  
  
  CONCLUSIONS
  Modifying the X-ray beam and foot rotation increases variability in JSW measurements. Use of urograms to evaluate radiological progression should be avoided. A change greater than 0.46 mm could define radiological hip OA progression.
authors: Clinique de Rhumatologie, Hôpital Cochin, AP-HP, Paris, France.
authors: G R
authors: GR
authors: Auleley
authors: A
authors: A
authors: Duche
authors: J L
authors: JL
authors: Drape
authors: M
authors: M
authors: Dougados
authors: P
authors: P
authors: Ravaud
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006621:Hip Joint / Q000473:pathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000000981:diagnostic imaging / Q000473:pathology*; D010388:Pelvis / Q000000981:diagnostic imaging; D011859:Radiography; D015203:Reproducibility of Results; D012399:Rotation