title: C-OnSite ® for intraoperative 3D control of pedicular screw positions.
abstract: BACKGROUND
  Two-dimensional image guidance and navigation can help to reduce the number of misplaced pedicle screws, but do not completely prevent misplacement. This experimental, retrospective, non-inferiority study was designed to evaluate and compare the efficacy of a novel 3D imaging technique versus conventional postoperative CT-scan, for intra-operative determination of pedicle screw position accuracy.
  
  
  METHODS
  The capacity of C-OnSite® to intraoperatively assess screw placement was evaluated in 28 clinical cases and 23 deliberately misplaced screws in a cadaver model, and compared to placement accuracy determined by standard CT. The position of each implant, as viewed by both modalities, was graded by three neurosurgeons, one orthopaedic-surgeon and one radiologist. The intermodal variance determined the difference between CT- and C-OnSite® results for each observer, while the inter-observer variance measured the difference between ratings of the same modality by different observers.
  
  
  RESULTS
  C-OnSite® successfully assessed 120/138 screws (25/28 cases). Mean procedural fluoroscopy time was 132 ± 51 s, and 40 ± 16s per C-OnSite® scan. The average inter-modality variance was ,15 % with mismatches >1° between C-OnSite® and the gold-standard imaging technique in only 2 % of the comparisons. Average inter-observer variances were about similar (12 % for CT and 18 % for C-OnSite®), with deviations of >1° reaching 1 % for CT and 3 % for C-OnSite®. Individual variances between experienced only observers differed even less.
  
  
  CONCLUSIONS
  C-OnSite® is a feasible, reliable and intuitive means of intraoperatively visualizing pedicle screw positions and might render the majority of postoperative CTs superfluous. C-OnSite® might help avoid re-operations for screw re-positioning.
authors.affiliation: Department of Neurosurgery, University Medical Centre, Johannes Gutenberg-University Mainz, Langenbeckstr. 1, 55131, Mainz, Germany, sven.kantelhardt@unimedizin-mainz.de.
authors.forename: Sven Rainer
authors.initials: SR
authors.lastname: Kantelhardt
authors.forename: Naureen
authors.initials: N
authors.lastname: Keric
authors.forename: Jens
authors.initials: J
authors.lastname: Conrad
authors.forename: Amr
authors.initials: A
authors.lastname: Nimer
authors.forename: Raymund
authors.initials: R
authors.lastname: Woo
authors.forename: Laura
authors.initials: L
authors.lastname: Varich
authors.forename: Alf
authors.initials: A
authors.lastname: Giese
mesh_terms: D005471:Fluoroscopy / Q000295:instrumentation; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D008159:Lumbar Vertebrae / Q000601:surgery*; D038361:Neuronavigation / Q000295:instrumentation*; D015588:Observer Variation; D065289:Pedicle Screws; D012086:Reoperation; D012189:Retrospective Studies; D012371:Robotics / Q000295:instrumentation*; D012984:Software; D013122:Spinal Diseases / Q000601:surgery*; D016103:Spinal Fractures / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*