title: Development and validation of an automated and marker-free CT-based spatial analysis method (CTSA) for assessment of femoral hip implant migration: In vitro accuracy and precision comparable to that of radiostereometric analysis (RSA).
abstract: OBJECTIVE
  We developed a marker-free automated CT-based spatial analysis (CTSA) method to detect stem-bone migration in consecutive CT datasets and assessed the accuracy and precision in vitro. Our aim was to demonstrate that in vitro accuracy and precision of CTSA is comparable to that of radiostereometric analysis (RSA).
  
  
  METHODS
  Stem and bone were segmented in 2 CT datasets and both were registered pairwise. The resulting rigid transformations were compared and transferred to an anatomically sound coordinate system, taking the stem as reference. This resulted in 3 translation parameters and 3 rotation parameters describing the relative amount of stem-bone displacement, and it allowed calculation of the point of maximal stem migration. Accuracy was evaluated in 39 comparisons by imposing known stem migration on a stem-bone model. Precision was estimated in 20 comparisons based on a zero-migration model, and in 5 patients without stem loosening.
  
  
  RESULTS
  Limits of the 95% tolerance intervals (TIs) for accuracy did not exceed 0.28 mm for translations and 0.20° for rotations (largest standard deviation of the signed error (SD(SE)): 0.081 mm and 0.057°). In vitro, limits of the 95% TI for precision in a clinically relevant setting (8 comparisons) were below 0.09 mm and 0.14° (largest SD(SE): 0.012 mm and 0.020°). In patients, the precision was lower, but acceptable, and dependent on CT scan resolution.
  
  
  CONCLUSIONS
  CTSA allows detection of stem-bone migration with an accuracy and precision comparable to that of RSA. It could be valuable for evaluation of subtle stem loosening in clinical practice.
authors.affiliation: a Department or Orthopedic Surgery and Traumatology , Universitair Ziekenhuis Brussel , Brussels.|b Medische Beeldvorming en Fysische Wetenschappen (BEFY), Vrije Universiteit Brussel , Brussels.
authors.forename: Thierry
authors.initials: T
authors.lastname: Scheerlinck
authors.affiliation: c Department of Electronics and Informatics (ETRO) , Vrije Universiteit Brussel , Brussels.|d iMinds, Department of Medical IT , Gent.
authors.forename: Mathias
authors.initials: M
authors.lastname: Polfliet
authors.affiliation: c Department of Electronics and Informatics (ETRO) , Vrije Universiteit Brussel , Brussels.|d iMinds, Department of Medical IT , Gent.
authors.forename: Rudi
authors.initials: R
authors.lastname: Deklerck
authors.affiliation: b Medische Beeldvorming en Fysische Wetenschappen (BEFY), Vrije Universiteit Brussel , Brussels.|e Department of Radiology , Universitair Ziekenhuis Brussel , Brussels , Belgium .
authors.forename: Gert
authors.initials: G
authors.lastname: Van Gompel
authors.affiliation: b Medische Beeldvorming en Fysische Wetenschappen (BEFY), Vrije Universiteit Brussel , Brussels.|e Department of Radiology , Universitair Ziekenhuis Brussel , Brussels , Belgium .
authors.forename: Nico
authors.initials: N
authors.lastname: Buls
authors.affiliation: c Department of Electronics and Informatics (ETRO) , Vrije Universiteit Brussel , Brussels.|d iMinds, Department of Medical IT , Gent.
authors.forename: Jef
authors.initials: J
authors.lastname: Vandemeulebroucke
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D006621:Hip Joint / Q000000981:diagnostic imaging*; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D011475:Prosthesis Failure / Q000009:adverse effects*; D059869:Radiostereometric Analysis; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed / Q000379:methods*