title: Radiation- and reference base-free navigation procedure for placement of instruments and implants: application to retrograde drilling of osteochondral lesions of the knee joint.
abstract: OBJECTIVE
  A novel, radiation- and reference base-free procedure for placement of navigated instruments and implants was developed and its practicability and precision in retrograde drillings evaluated in an experimental setting.
  
  
  METHODS
  Two different guidance techniques were used: One experimental group was operated on using the radiation- and reference base-free navigation technique (Fluoro Free), and the control group was operated on using standard fluoroscopy for guidance. For each group, 12 core decompressions were simulated by retrograde drillings in different artificial femurs following arthroscopic determination of the osteochondral lesions. The final guide-wire position was evaluated by postoperative CT analysis using vector calculation.
  
  
  RESULTS
  High precision was achieved in both groups, but operating time was significantly reduced in the navigated group as compared to the control group. This was due to a 100% first-pass accuracy of drilling in the navigated group; in the control group a mean of 2.5 correction maneuvers per drilling were necessary. Additionally, the procedure was free of radiation in the navigated group, whereas 17.2 seconds of radiation exposure time were measured in the fluoroscopy-guided group.
  
  
  CONCLUSIONS
  The developed Fluoro Free procedure is a promising and simplified approach to navigating different instruments as well as implants in relation to visually or tactilely placed pointers or objects without the need for radiation exposure or invasive fixation of a dynamic reference base in the bone.
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, Friedrich Schiller University, Jena, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Müller
authors.forename: Florian
authors.initials: F
authors.lastname: Gras
authors.forename: Ivan
authors.initials: I
authors.lastname: Marintschev
authors.forename: Thomas
authors.initials: T
authors.lastname: Mückley
authors.forename: Gunter O
authors.initials: GO
authors.lastname: Hofmann
mesh_terms: D001182:Arthroscopy; D003198:Computer Simulation; D005240:Feasibility Studies; D005269:Femur / Q000601:surgery*; D005471:Fluoroscopy; D006801:Humans; D021621:Imaging, Three-Dimensional; D007718:Knee Injuries / Q000473:pathology / Q000601:surgery*; D007719:Knee Joint / Q000473:pathology / Q000601:surgery*; D008953:Models, Anatomic; D010008:Osteochondritis Dissecans / Q000601:surgery*; D025321:Surgery, Computer-Assisted / Q000295:instrumentation / Q000379:methods*