title: Spatial component position in total hip arthroplasty. Accuracy and repeatability with a new CT method.
abstract: OBJECTIVE
  3D detection of centerpoints of prosthetic cup and head after total hip arthroplasty (THA) using CT.
  
  
  METHODS
  Two CT examinations, 10 min apart, were obtained from each of 10 patients after THA. Two independent examiners placed landmarks in images of the prosthetic cup and head. All landmarking was repeated after 1 week. Centerpoints were calculated and compared.
  
  
  RESULTS
  Within volumes, all measurements of centerpoints of cup and head fell, with a 95% confidence, within one CT-voxel of any other measurement of the same object. Across two volumes, the mean error of distance between center of cup and prosthetic head was 1.4 mm (SD 0.73). Intra- and interobserver 95% accuracy limit was below 2 mm within and below 3 mm across volumes. No difference between intra- and interobserver measurements occurred. A formula for converting finite sets of point landmarks in the radiolucent tread of the cup to a centerpoint was stable. The percent difference of the landmark distances from a calculated spherical surface was within one CT-voxel. This data was normally distributed and not dependent on observer or trial.
  
  
  CONCLUSIONS
  The true 3D position of the centers of cup and prosthetic head can be detected using CT. Spatial relationship between the components can be analyzed visually and numerically.
authors.affiliation: Department of Hand Surgery, Södersjukhuset, Stockholm, Sweden. henrik.olivecrona@sos.sll.se
authors.forename: H
authors.initials: H
authors.lastname: Olivecrona
authors.forename: L
authors.initials: L
authors.lastname: Weidenhielm
authors.forename: L
authors.initials: L
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: T
authors.initials: T
authors.lastname: Jonson
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D005500:Follow-Up Studies; D025981:Hip Injuries / Q000000981:diagnostic imaging* / Q000601:surgery*; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D015588:Observer Variation; D011237:Predictive Value of Tests; D017755:Prosthesis Fitting / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*