title: Validation of a statistical shape model-based 2D/3D reconstruction method for determination of cup orientation after THA.
abstract: OBJECTIVE
  The aim of this study was to validate the accuracy and reproducibility of a statistical shape model-based 2D/3D reconstruction method for determining cup orientation after total hip arthroplasty. With a statistical shape model, this method allows reconstructing a patient-specific 3D-model of the pelvis from a standard AP X-ray radiograph. Cup orientation (inclination and anteversion) is then calculated with respect to the anterior pelvic plane that is derived from the reconstructed model.
  
  
  METHODS
  The validation study was conducted retrospectively on datasets of 29 patients (31 hips). Among them, there were 15 men (15 hips) and 14 women (16 hips). The average age of the patients was 69.4±8.5 (49-82) years. Each dataset has one postoperative X-ray radiograph and one postoperative CT scan. The postoperative CT scan for each patient was used to establish the ground truth for the cup orientation. The cup anteversion and inclination that were calculated from the 2D/3D reconstruction method were compared to the associated ground truth. To validate reproducibility and reliability, two observers performed measurements for each dataset twice in order to measure the reproducibility and the reliability of the 2D/3D reconstruction method.
  
  
  RESULTS
  Our validation study demonstrated a mean accuracy of 0.4 ± 1.8° (-2.6° to 3.3°) for inclination and a mean accuracy of 0.6±1.5° (-2.0° to 3.9°) for anteversion. Through the Bland-Altman analysis, no systematic errors in accuracy were detected. The method showed very good consistency for both parameters.
  
  
  CONCLUSIONS
  Our validation results demonstrate that the statistical shape model-based 2D/3D reconstruction-based method is an accurate, consistent, and reproducible technique to measure cup orientation from postoperative X-ray radiographs. The best results were achieved with radiographs including the bilateral anterior superior iliac spines and the cranial part of non-fractured pelvises.
authors.affiliation: Institute for Surgical Technology and Biomechanics, University of Bern, Stauffacherstrasse 78, 3014, Bern, Switzerland. guoyan.zheng@ieee.org
authors.forename: G
authors.initials: G
authors.lastname: Zheng
authors.forename: J
authors.initials: J
authors.lastname: von Recum
authors.forename: L-P
authors.initials: LP
authors.lastname: Nolte
authors.forename: P A
authors.initials: PA
authors.lastname: Grützner
authors.forename: S D
authors.initials: SD
authors.lastname: Steppacher
authors.forename: J
authors.initials: J
authors.lastname: Franke
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging* / Q000601:surgery; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D016001:Confidence Intervals; D016208:Databases, Factual; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D015588:Observer Variation; D011857:Radiographic Image Interpretation, Computer-Assisted; D012086:Reoperation / Q000379:methods; D015203:Reproducibility of Results; D012189:Retrospective Studies; D018570:Risk Assessment; D018709:Statistics, Nonparametric; D014057:Tomography, X-Ray Computed / Q000379:methods