title: Acetabular component migration in total hip arthroplasty using CT and a semiautomated program for volume merging.
abstract: OBJECTIVE
  To develop a non-invasive method for detection of acetabular cup migration after total hip arthroplasty (THA) with a higher degree of accuracy than routine plain radiography.
  
  
  METHODS
  Two CT examinations, 10 min apart, were obtained from each of 10 patients that had undergone THA. Using an in-house developed semiautomated program for volume merging, the pelves in the two examinations were fused and the acetabular cup was visually and numerically evaluated to test the method's accuracy in detecting migration.
  
  
  RESULTS
  In the visual evaluation of the best match a 1-mm translation of the cup was detectable. The numerical evaluation, comparing landmarks placed in the images of the acetabular cup and the head of the femur component in the two examinations, showed the mean difference in orientation of acetabular axes to be 2.5 degrees, the mean distance between centre of cup face to be 2.5 mm and the mean distance between centre of the head of the prosthetic femoral component to be 1 mm.
  
  
  CONCLUSIONS
  This method has a significantly higher accuracy than routine plain radiography in detecting acetabular cup migration and could be used in clinical practice. It gives both a visual and a numerical correlate to migration.
authors.affiliation: Department of Radiology , Karolinska Hospital, Stockholm, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Olivecrona
authors.forename: J
authors.initials: J
authors.lastname: Crafoord
authors.forename: H
authors.initials: H
authors.lastname: Olivecrona
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
authors.forename: L
authors.initials: L
authors.lastname: Svensson
authors.forename: L
authors.initials: L
authors.lastname: Weidenhielm
mesh_terms: D000465:Algorithms; D005548:Foreign-Body Migration / Q000000981:diagnostic imaging*; D006622:Hip Prosthesis; D006801:Humans; D011475:Prosthesis Failure; D014057:Tomography, X-Ray Computed / Q000379:methods*