title: Pelvic tilt makes acetabular cup navigation inaccurate.
abstract: BACKGROUND
  Modern navigation techniques allow precise positioning of the acetabular cup relative to the anterior pelvic plane. Variations in pelvic tilt will affect the resulting spatial orientation of the cup.
  
  
  METHODS
  We measured pelvic tilt in 30 volunteers with an inclinometer combined with an ultrasonographic position measurement system. A mathematical algorithm was developed to calculate the resulting cup position measured on standard radiographs, depending on pelvic tilt.
  
  
  RESULTS
  Average pelvic tilt at rest was -4 degrees in the lying position and -8 degrees in the standing position, and ranged from -27 degrees to +3 degrees. Pelvic reclination of 1 degree will lead to functional anteversion of the cup of approximately 0.7 degree.
  
  
  CONCLUSIONS
  Pelvic tilt makes navigation systems referring to the anterior plane inaccurate.
authors.affiliation: Department of Orthopaedic Surgery, University of Tuebingen, Germany. burkhard.lembeck@med.uni-tuebingen.de
authors.forename: Burkhard
authors.initials: B
authors.lastname: Lembeck
authors.forename: Otto
authors.initials: O
authors.lastname: Mueller
authors.forename: Patrik
authors.initials: P
authors.lastname: Reize
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Wuelker
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000502:physiology*; D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D010388:Pelvis / Q000000981:diagnostic imaging / Q000502:physiology*; D011187:Posture; D011859:Radiography; D012680:Sensitivity and Specificity; D014463:Ultrasonography