title: A new technique for diagnosis of acetabular cup loosening using computed tomography: preliminary experience in 10 patients.
abstract: OBJECTIVE
  Considerable migration of the acetabular cup is required for diagnosis of loosening by conventional radiography. We have developed a new clinically applicable method for assessment of cup loosening using computed tomography (CT).
  
  
  METHODS
  10 patients scheduled for revision hip replacement due to suspected wear or loosening were scanned twice with CT under torsion loading of the prosthesis. Two independent examiners assessed each patient with respect to motion of the acetabular cup relative to the pelvis using CT volume registration. The CT measurements were compared to findings at revision surgery.
  
  
  RESULTS
  The method was applicable in 8 of the 10 patients. 1 patient had a severe tremor. In 1 patient, surgery revealed that the hip was ankylotic due to massive ectopic bone formation. This left 8 patients that could be evaluated. 4 cups were loose at surgery, and 3 of these cups could be seen to be mobile by CT. 4 cups that were stable on revision were accurately diagnosed as not being mobile by CT. Movements of less than 1 millimeter between bone and prosthesis could not be distinguished from errors in CT acquisition and volume registration. There was good agreement between the two observers.
  
  
  CONCLUSIONS
  Movement of loose acetabular cups during torsion loading could be detected using CT volume registration. It was sensitive to cup movement in 3 out of 4 cases of loose cups. The method was specific and yielded no false positive results.
authors.affiliation: Department of Hand Surgery, Södersjukhuset, Stockholm. henrik.olivecrona@sodersjukhuset.se
authors.forename: Henrik
authors.initials: H
authors.lastname: Olivecrona
authors.forename: Lotta
authors.initials: L
authors.lastname: Olivecrona
authors.forename: Lars
authors.initials: L
authors.lastname: Weidenhielm
authors.forename: Marilyn E
authors.initials: ME
authors.lastname: Noz
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Kardos
authors.forename: Gerald Q
authors.initials: GQ
authors.lastname: Maguire
authors.forename: Michael P
authors.initials: MP
authors.lastname: Zeleznik
authors.forename: Peter
authors.initials: P
authors.lastname: Aspelin
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging*; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011475:Prosthesis Failure; D012086:Reoperation; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*