Frameless optical computer-aided tracking of a microscope for otorhinologyand skull base surgery

Objectives: To integrate a digitally controlled operating microscope withou t a laser autofocus system into a frameless optical computer-aided surgery system and to test the accuracy and usability of this system in otorhinolog ical surgery. Design: Experimental study and case series. Setting: Department of Oto-Rhino-Laryngology, Head and Neck Surgery, Insels pital, and the Maurice E. Muller Institute for Biomechanics, University of Bern, Bern, Switzerland. Patients: Eight computer-aided microscopic surgical procedures were perform ed between January and October 2000 on patients with various diseases of th e anterior and lateral skull base. Results: The practical accuracy of the navigated microscope on the lateral side of a cadaver skull was 2.27 +/- 0.25 mm and on the anterior side of th e same skull was 2.07 +/- 0.35 mm. In all 8 cases of computer-aided microsc opic surgery, no complications occurred. Clinical inaccuracy was 2 to 3 mm. Conclusion: Integration of a low-cost, non-laser autofocus microscope into our computer-aided surgery system was successfully performed and offers sur geons the ability to combine the precise optics of the operating microscope with the localization power of a computer-aided system.