title: Is Model-based Radiostereometric Analysis Suitable for Clinical Trials of a Cementless Tapered Wedge Femoral Stem?
abstract: BACKGROUND
  In clinical trials of THA, model-based radiostereometric analysis (RSA) techniques may be less precise than conventional marker-based RSA for measurement of femoral stem rotation. We verified the accuracy and clinical precision of RSA based on computer-aided design models of a cementless tapered wedge femoral stem.
  
  
  OBJECTIVE
  We asked: (1) Is the accuracy of model-based RSA comparable to that of marker-based RSA? (2) What is the clinical precision of model-based RSA?
  
  
  METHODS
  Model-based RSA was performed using combined three-dimensional computer-aided design models of the stem and head provided by the implant manufacturer. The accuracy of model-based RSA was compared with that of marker-based RSA in a phantom model using micromanipulators for controlled translation in three axes (x, y, z) and rotation around the y axis. The clinical precision of model-based RSA was evaluated by double examinations of patients who had arthroplasties (n = 24) in an ongoing trial. The clinical precision was defined as being at an acceptable level if the number of patients needed for a randomized trial would not differ from a trial done with conventional marker-based RSA (15-25 patients per group).
  
  
  RESULTS
  The accuracy of model-based RSA was 0.03 mm for subsidence (translation along the y axis) (95% CI for the difference between RSA measurements and actual displacement measured with micrometers, -0.03-0.00) and 0.39° for rotation around the y axis (95% CI, -0.41 to -0.06). The accuracy of marker-based RSA was 0.06 mm for subsidence (95% CI, -0.04-0.01; p = 0.728 compared with model-based RSA) and 0.18° for the y axis rotation (95% CI, -0.23 to -0.07; p = 0.358). The clinical precision of model-based RSA was 0.14 mm for subsidence (95% CI for the difference between double examinations, -0.02-0.04) and 0.79° for the y axis rotation (95% CI, -0.16-0.18).
  
  
  CONCLUSIONS
  The accuracy of model-based RSA for measurement of the y axis rotation was not quite as high as that of marker-based RSA, but its clinical precision is at an acceptable level.
  
  
  CONCLUSIONS
  Model-based RSA may be suitable for clinical trials of cementless tapered wedge femoral stem designs.
authors.affiliation: Orthopaedic Research Unit, Department of Orthopaedic Surgery and Traumatology, University of Turku and Turku University Hospital, T-hospital, PL 52, 20521, Turku, Finland.
authors.forename: Sanaz
authors.initials: S
authors.lastname: Nazari-Farsani
authors.affiliation: Orthopaedic Research Unit, Department of Orthopaedic Surgery and Traumatology, University of Turku and Turku University Hospital, T-hospital, PL 52, 20521, Turku, Finland.
authors.forename: Sami
authors.initials: S
authors.lastname: Finnilä
authors.affiliation: Orthopaedic Research Unit, Department of Orthopaedic Surgery and Traumatology, University of Turku and Turku University Hospital, T-hospital, PL 52, 20521, Turku, Finland.
authors.forename: Niko
authors.initials: N
authors.lastname: Moritz
authors.affiliation: Medical Imaging Centre of Southwest Finland, Turku University Hospital, Kiinamyllynkatu 4-8, 20520, Turku, Finland.
authors.forename: Kimmo
authors.initials: K
authors.lastname: Mattila
authors.affiliation: Orthopaedic Research Unit, Department of Orthopaedic Surgery and Traumatology, University of Turku and Turku University Hospital, T-hospital, PL 52, 20521, Turku, Finland.
authors.forename: Jessica J
authors.initials: JJ
authors.lastname: Alm
authors.affiliation: Orthopaedic Research Unit, Department of Orthopaedic Surgery and Traumatology, University of Turku and Turku University Hospital, T-hospital, PL 52, 20521, Turku, Finland. hannu.aro@utu.fi.
authors.forename: Hannu T
authors.initials: HT
authors.lastname: Aro
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000523:psychology*; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005260:Female; D005269:Femur / Q000503:physiopathology / Q000601:surgery*; D006621:Hip Joint / Q000503:physiopathology / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D019047:Phantoms, Imaging; D011474:Prosthesis Design; D059869:Radiostereometric Analysis / Q000295:instrumentation; D015203:Reproducibility of Results; D012107:Research Design; D012399:Rotation; D016896:Treatment Outcome