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.

Evaluation of the accuracy of three different computer-aided surgery systems in dental implantology: optical tracking vs. stereolithographic splint systems.

OBJECTIVES: In dental implant surgery, computer-aided surgery (CAS) techniques can provide a high medical benefit. Two different techniques are established for transferring a CAS treatment planning to the patient: the use of surgical templates (splints) or intraoperative navigation using optical tracking. The aim of this study was to evaluate the total application accuracy of three different CAS systems (Artma virtual patient, RoboDent LapAccedo, Materialise SurgiGuide): two featuring optical tracking, one featuring stereolithographically manufactured splints. MATERIALS AND METHODS: A total of 120 implants were placed into 20 human cadaver mandibles. Preoperative computed tomography (CT) scans imported to the corresponding software were used to plan the implant positions on the computer. Implant placement was performed using either optical tracking or stereolithographic splints. Postoperative CT scans were used to obtain the achieved implant positions. A semi-automatic approach was developed to compare planned and achieved implant positions. Deviations between planned and achieved positions were measured for each implant in position (Delta xy), depth (Delta z) and axis (Delta phi). CONCLUSION: Despite the different techniques of transfer, no statistically significant differences were found between all groups. The accuracy achieved corresponded well with the spatial resolution of the CT Scans used.

Virtual endoscopy on a portable navigation system for ENT surgery.

Virtual endoscopy is considered as an ideal aid assessing the complex anatomy of patients and has already been evaluated in several clinical studies. However, due to the increasing quality of modern CT- and MRT-images, present virtual-endoscopy software relies on powerful hardware. In this contribution virtual endoscopy on a portable navigation system for ENT surgery is proposed. The portable navigation system features a tablet pc to ensure a device that does not need much space in the operating room.

Model for nerve visualization in preoperative image data based on intraoperatively gained EMG signals.

While removing bone tissue of the mastoid, the facial nerve is at risk of being injured. In this contribution a model for nerve visualization in preoperative image data based on intraoperatively gained EMG signals is proposed. A neuro monitor can assist the surgeon locating and preserving the nerve. With the proposed model gained EMG signals can be spatially related to the patient resp. the image data. During navigation the detected nerve course will be visualized and hence permanently available for assessing the situs.

FESS control: realization and evaluation of navigated control for functional endoscopic sinus surgery.

In this paper, a new system for navigated control in functional endoscopic sinus surgery (FESS) is presented. The system allows the safe and convenient use of a shaver that can be enabled by the surgeon only within a specified working space. Preoperatively, the surgeon defines this working space in the axial slices of the CT scan. During the surgery, the positions of the shaver and patient are tracked by an optical navigation system, which calculates whether the shaver is within the working space. The navigated control electronics receives a signal from the navigation system and disables the shaver if it is outside the working space. If the shaver is inside the working space, the surgeon can set its speed freely with a foot pedal. Experimental evaluation shows that the system allows convenient and intuitive safe removal of inflamed tissue while protecting sensitive structures. The clinical applicability was proven in a clinical trial with 10 patients.