title: A comparison of optical and electromagnetic computer-assisted navigation systems for fluoroscopic targeting.
abstract: OBJECTIVE
  Freehand targeting using fluoroscopic guidance is routine for placement of interlocking screws associated with intramedullary nailing and for insertion of screws for reconstruction of pelvic and acetabular injuries. New technologies that use fluoroscopy with the assistance of computer guidance have the potential to improve accuracy and reduce radiation exposure to patient and surgeon. We sought to compare 2 fluoroscopic navigation tracking technologies, optical and electromagnetic versus standard freehand fluoroscopic targeting in a standardized model.
  
  
  METHODS
  Three experienced orthopaedic trauma surgeons placed 3.2-mm guide pins through test foam blocks that simulate cancellous bone. The entry site for each pin was within a circular (18-mm) entry zone. On the opposite surface of the test block (130-mm across), the target was a 1-mm-diameter radioopaque spherical ball marker. Each surgeon placed 10 pins using freehand targeting (control group) navigation using Medtronic iON StealthStation (Optical A), navigation using BrainLAB VectorVision (Optical B), or navigation using GE Medical Systems InstaTrak 3500 system (EM).
  
  
  METHODS
  Data were collected for accuracy (the distance from the exit site of the guidewire to the target spherical ball marker), fluoroscopy time (seconds), and total number of individual fluoroscopy images taken.
  
  
  RESULTS
  The 2 optical systems and the electromagnetic system provided significantly improved accuracy compared to freehand technique. The average distance from the target was significantly (3.5 times) greater for controls (7.1 mm) than for each of the navigated systems (Optical A = 2.1 mm, Optical B = 1.9 mm EM = 2.4 mm; P < .05). Accuracy was similar for the 3 navigated systems, (P > 0.05). The ability to place guidewires in a 5-mm safe zone surrounding the target sphere was also significantly improved with the optical systems and the EM system (99% of wires in the safe zone) compared to controls (47% in the safe zone) (P < 0.002). Safe zone placement was similar among the 3 navigated systems (P > 0.05). Fluoroscopy time (seconds) and number of fluoroscopy images were similar among the three navigated groups (P > 0.05). Each of these parameters was significantly less when using the computer-guided systems than for freehand-unguided insertion (P < 0.01).
  
  
  CONCLUSIONS
  Both optical and electromagnetic computer-assisted guidance systems have the potential to improve accuracy and reduce radiation use for freehand fluoroscopic targeting in orthopaedic surgery.
authors.affiliation: Washington University Orthopedics, Washington University School of Medicine , St. Louis, Missouri, USA.
authors.forename: William M
authors.initials: WM
authors.lastname: Ricci
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Russell
authors.forename: David M
authors.initials: DM
authors.lastname: Kahler
authors.forename: Lauralan
authors.initials: L
authors.lastname: Terrill-Grisoni
authors.forename: Patrick
authors.initials: P
authors.lastname: Culley
mesh_terms: D001858:Bone Nails; D055590:Electromagnetic Phenomena / Q000295:instrumentation*; D005471:Fluoroscopy / Q000295:instrumentation / Q000379:methods; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D055095:Optics and Photonics / Q000295:instrumentation*; D019637:Orthopedic Procedures / Q000379:methods; D011829:Radiation Dosage; D015203:Reproducibility of Results; D025321:Surgery, Computer-Assisted; D013997:Time Factors