title: Inter- and intraobserver variability in the postoperative evaluation of transpedicular stabilization: computed tomography versus magnetic resonance imaging.
abstract: BACKGROUND
  Computed tomography (CT) represents the state of the art for the postoperative verification of the implant position after transpedicular stabilizations. Magnetic resonance imaging (MRI) has not challenged the CT, yet, because of susceptibility artifacts but would be favorable as a diagnostic tool for its excellent soft-tissue qualities.
  
  
  OBJECTIVE
  A study that analyzed if an artifact-reduced MRI could overcome this problem and provide sufficient data for the postoperative assessment was conducted.
  
  
  METHODS
  The study design was a radiologic comparison of CT and MRI techniques evaluating pedicle screw placement after spinal fusion.
  
  
  METHODS
  Fifty consecutive patients were given an MRI and a CT after a transpedicular stabilization surgery. Thirty-eight patients suffered from degenerative spinal disorders; three surgeries had become necessary because of spondylodiscitis, eight patients suffered from metastatic vertebrae destruction, and one patient experienced a fracture.
  
  
  METHODS
  Any contact of a malpositioned pedicle screw with the dura and/or radicular structures was identified as an implant-associated complication and was compared with postoperative clinical patient findings.
  
  
  METHODS
  In total, 338 pedicular screws were analyzed in regard to their intrapedicular position. The double-blind evaluation of MRI and CT data was carried out by two radiologists and two spine surgeons. Accuracy of the CT analysis was calculated based on the interobserver agreement of 100%. Magnetic resonance imaging accuracy was calculated.
  
  
  RESULTS
  The interobserver accuracy of the CT data amounted to a median of 89.8% and in the MRI data of 86.7%. Intraobserver comparisons showed a significant difference between CT and magnetic resonance evaluations in one observer (kappa=0.293). In all other observers, the results were concordant with kappa values from kappa=0.328 to kappa=0.702. There was a high degree of agreement regarding the diagnosis of malpositioned pedicle screw and corresponding clinical symptoms between both techniques.
  
  
  CONCLUSIONS
  The presented data show that artifact-reduced MRI is equivalent to CT imaging in the postoperative evaluation of titanium spinal rod-screw systems. We therefore conclude that MRI should be considered as an alternative tool for the golden standard CT for postoperative imaging controls for its advantages in soft-tissue analysis.
authors.affiliation: Department of Orthopedics, Charité-Universitaetsmedizin, 10117 Berlin, Germany. stephan.tohtz@charite.de
authors.forename: Stephan W
authors.initials: SW
authors.lastname: Tohtz
authors.forename: Patrick
authors.initials: P
authors.lastname: Rogalla
authors.forename: Matthias
authors.initials: M
authors.lastname: Taupitz
authors.forename: Carsten
authors.initials: C
authors.lastname: Perka
authors.forename: Tobias
authors.initials: T
authors.lastname: Winkler
authors.forename: Michael
authors.initials: M
authors.lastname: Putzier
mesh_terms: D016477:Artifacts; D001863:Bone Screws; D018450:Disease Progression; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000592:standards / Q000706:statistics & numerical data*; D008297:Male; D015588:Observer Variation; D011183:Postoperative Complications / Q000000981:diagnostic imaging* / Q000473:pathology*; D012015:Reference Standards; D013122:Spinal Diseases / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation; D014057:Tomography, X-Ray Computed / Q000592:standards / Q000706:statistics & numerical data*