title: Use of internal fiducial markers in frameless stereotactic navigational systems during spinal surgery: technical note.
abstract: OBJECTIVE
  The use of frameless stereotaxy has expanded the spine surgeon's ability to perform surgical procedures with instrumentation in areas of narrow anatomic tolerance. In many circumstances, however, it is difficult to register the frameless stereotactic probe using known anatomic landmarks. This occurs typically because landmarks are indistinct, and congenital or surgical defects limit the availability of anatomic fiducials. We propose an accurate and efficient method for registering the frameless stereotactic probe for spinal surgery when a staged procedure is planned.
  
  
  METHODS
  During the first stage of a planned two-stage procedure, a minimum of four cranial fiducial screws are implanted in the posterior element of each vertebra in which stereotactic registration is desired. Stage 1 is completed, and all suture closure is performed. A computed tomographic scan formatted for the frameless stereotactic unit is obtained postoperatively. In the second stage of surgery, registration is performed using cranial screws as internal fiducial markers.
  
  
  RESULTS
  Registration is performed easily and quickly using cranial screws as internal fiducial markers. No more than four registration points are necessary to calibrate the system to accuracy within 1.5 mm.
  
  
  CONCLUSIONS
  Implantation of fiducial markers during Stage 1 of a complex staged spinal surgery renders the frameless stereotactic navigational system registration extremely fast and accurate. We advocate the technique to enhance the use of frameless navigational systems for reliable and quick registration of the spine.
authors: Department of Neurological Surgery, Northwestern University Medical School, Chicago, Illinois, USA. ssalehi@nwu.edu
authors: S A
authors: SA
authors: Salehi
authors: S L
authors: SL
authors: Ondra
mesh_terms: D001863:Bone Screws; D006801:Humans; D020007:Implants, Experimental; D013131:Spine / Q000601:surgery*; D013238:Stereotaxic Techniques / Q000295:instrumentation