The influence of various registration procedures upon surgical accuracy during navigated controlled petrous bone surgery.

OBJECTIVE: The goal of this study was to investigate the dependence of surgical accuracy with a navigated controlled (NC) drill on selected registration procedures. STUDY DESIGN: The target registration error of the instrument and the maximum proximity to a typical high-risk structure (facial nerve) were determined within an artificial petrous bone. SETTING: The studies took place in two groups: group 1, navigation bow with six integrated markers and attachment at the upper jaw, and group 2, landmark registration with four titanium microscrews. Measurement of the target registration error took place at three targets (3 titanium screws) with 20 repeated registration procedures via evaluation of the deviation between a target and the indicated position in the navigation data. SUBJECTS AND METHODS: For measurement of the conversion accuracy of the planned cavity, 20 petrous bone models were milled by inexperienced test subjects. The evaluation of 20 cavities was conducted via a microscope by five jurors. RESULTS: Registration accuracy showed a maximum deviation between the actual position achieved and the computed position in the navigation system of 1.73 mm in group 1 and 0.93 mm in group 2. In group 1, the nerve in five of 20 cases was damaged, and a maximum penetration into the nerve of 1.5 mm (0.25 mm SD; milled beyond) was measured. In group 2, the facial nerve was not damaged at all, and a maximum deviation of 0.5 mm (0.63 mm SD; stopped before) was measured. CONCLUSION: The results for registration and conversion accuracy are significantly better for the landmark-based registration than with the registration of the patient model with registration bow on the upper jaw.

The navigation-controlled drill in temporal bone surgery: a feasibility study.

BACKGROUND: This study examines the feasibility of a navigation-controlled (NC) drill for surgery on the petrosal bone in an experimental environment. According to the principle of NC, the drill is to be switched off automatically once the borders of the workspace are exceeded during a mastoidectomy. MATERIALS AND METHODS: The registration is based on an optical navigation system with navigation software (MiMed). As surgery engine, the Unidrive-system (Karl Storz GmbH & CO. Kg, Tuttlingen, Germany) was integrated. The definition of the workspace was performed manually in axial computed tomography (CT) slices of the petrosal bone phantom. The mastoidectomy on the model was accomplished in three runs with 10 trial surgeons altogether (5 experienced [exp.] in otologic (ear) surgery, 5 inexperienced [nonexp.]). During each run, the following were logged: the total length of time for the procedure as well as the number and extent of injuries to the risk structures (facial nerve, horizontal semicircular canal, sigmoid sinus). The resultant petrosal bone cavities were measured on the CT. RESULTS: The time for the segmentation of the workspace for the mastoidectomy amounted to 17 minutes. The mean value of the drilling (e.g., milling) performance ranges from 6.61 mm3/s (group 1 [nonexp. + NC]), 9.62 mm3/s (group 2 [exp. w/o NC]), to 10.08 mm3/s (group 3 [exp. + NC]). The relative deviation to the segmented volume amounts to +7.4% (794.3 mm3) for group 1, -39.9% for group 2, and -34% (3,647.0 mm3) for group 3. In the groups with NC guidance of the drill, no damage to a risk structure could be logged. In the group of exp. ear surgeons without NC assistance, one injury to the facial nerve in the petrosal bone phantom occurred. DISCUSSION: The results that follow prove the fundamental feasibility of an NC drill for surgery of the petrosal bone using the example of the simple mastoidectomy in the laboratory test. When using NC, tissue resection is faster, more precise, and has fewer related complications than the same procedure without. The results offer a very promising basis for the introduction of a newly conceived system to the procedure of NC surgery on the petrosal bone. The device configuration used here was originally conceived for NC guidance of a shaver in functional endoscopic sinus surgery. Individual errors will have to be mitigated through the new version of the control unit presently in development.