title: [Misinterpretation of the anteversion in computer-assisted acetabular cup navigation as a result of a simplified palpation method of the frontal pelvic plane].
abstract: OBJECTIVE
  Computer assisted navigation of the acetabular cup in THR requires reliable digitalisation of bony landmarks defining the frontal pelvic plane by user driven palpation. According to the system recommendations the subcutaneous fat should be held aside during epicutaneous digitalization. To improve intraoperative practicability this is often neglected in the symphysis area. In these cases the fat is just compressed and not pushed aside.
  
  
  METHODS
  In this study soft tissue thickness was assessed by ultrasound and pelvic geometry was measured in 72 patients to quantify potential misinterpretation of cup anteversion triggered by the simplified palpation. As reference we employed data of the same patients that had been acquired by recommended palpation.
  
  
  RESULTS
  Anteversion misinterpretation averaged at 8.2 degrees with extremes from 2 to 24 degrees. There were no correlations between soft tissue thickness or misinterpretation and body weight, height and pelvic size. Anteversion misinterpretation was highly significant worse compared to the reference data.
  
  
  CONCLUSIONS
  In 31 % of the patients the anteversion misinterpretation of a navigation system would have been wrong by over 10 degrees and in 81 % over 5 degrees . Therefore the simplified palpation should not be utilized. For epicutaneous digitalization of the bony landmarks it is mandatory to push the subcutaneous fat aside.
authors.affiliation: Orthopädische Universitätsklinik, Stiftung Friedrichsheim, Frankfurt am Main. j.richolt@friedrichsheim.de
authors.forename: J A
authors.initials: JA
authors.lastname: Richolt
authors.forename: M E
authors.initials: ME
authors.lastname: Rittmeister
mesh_terms: D000077:Acetabulum / Q000601:surgery*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data*; D003951:Diagnostic Errors / Q000517:prevention & control; D005260:Female; D005858:Germany / Q000453:epidemiology; D006801:Humans; D008297:Male; D019300:Medical Errors / Q000517:prevention & control* / Q000706:statistics & numerical data*; D008875:Middle Aged; D010173:Palpation / Q000706:statistics & numerical data*; D010388:Pelvis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D025321:Surgery, Computer-Assisted / Q000379:methods / Q000706:statistics & numerical data*