title: Model studies on acetabular component migration in total hip arthroplasty using CT and a semiautomated program for volume merging.
abstract: OBJECTIVE
  Validation of a non-invasive CT method for detection of acetabular cup migration after total hip arthroplasty in a phantom study.
  
  
  METHODS
  26 CT examinations were obtained of a pelvic model while altering the position of the acetabular cup. Using a previously described program for volume merging, the pelvi in different examinations were fused and the 3D alterations of the position of the acetabular cup were evaluated visually and numerically and correlated to direct measurements on the model.
  
  
  RESULTS
  Visually, two independent examiners differentiated between 0, 1 and 2 to 3 mm migration with 100% specificity and sensitivity. Numerically, the mean error over all cases between model and CT measurements was 0.04 mm (SD +/- 0.33). The mean absolute error between model and CT data was 0.26 mm (SD +/- 0.19). Intra- and interobserver 95% accuracy and repeatability limits were below 0.5/0.7 mm, respectively. No significant interobserver difference occurred. The data were normally distributed and not dependent on observer.
  
  
  CONCLUSIONS
  The accuracy of this non-invasive method out-performs routine plain radiography. The method gives both visual and numerical correlates to migration and can be used in clinical practice.
authors.affiliation: Department of Radiology, Karolinska Hospital, Stockholm, Sweden. lotta.olivecrona@ks.se
authors.forename: L
authors.initials: L
authors.lastname: Olivecrona
authors.forename: H
authors.initials: H
authors.lastname: Olivecrona
authors.forename: L
authors.initials: L
authors.lastname: Weidenhielm
authors.forename: M E
authors.initials: ME
authors.lastname: Noz
authors.forename: G Q
authors.initials: GQ
authors.lastname: Maguire
authors.forename: M P
authors.initials: MP
authors.lastname: Zeleznik
mesh_terms: D019644:Arthroplasty, Replacement, Hip; D005548:Foreign-Body Migration / Q000000981:diagnostic imaging*; D006622:Hip Prosthesis; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D019047:Phantoms, Imaging; D011475:Prosthesis Failure; D014057:Tomography, X-Ray Computed