Experiences with peroperative navigation in bimaxillary orthognatic surgery: a view on the patient-mounted hardware components C. Politis, L. Vrielinck, S. Schepers, J Orye Yi Sun, Bart Falter, Alireza Parhiz Ziekenhuis Oost Limburg Genk
BrainLab Navigation System Camera
Monitor
Pointer
Navigation star
(skull reference base)
+ SOFTWARE
preoperative procedure check of the accuracy with the Z-touch
Peroperative procedure step 1: fixation of the navigation star on patients head SKULL BASED STAR : fixation screw HEAD BAND
Procedure Step 2: matching the patient to the CBCT image SURFACE LASER SCANNING
Laser scanner was used to sample the surface of patient's face
surface laser scanning is done AFTER nasal intubation and fixation of the star to the skull
Although computer states: “ Surface registration succeeded with good precision”….
Dental middle line is off to the right side
Sagittal measurement: an error of about 2mm to the tip edge of the upper incisor
Head Band
Fixed Star
Total
Less optimized/optimized Surface matching
2
1
3
Good accuracy with error Surface matching
1
7
8
0
6
6
3
14
17
Good accuracy Total Test
Surface matching
6/17 = 35%
Problem 1: the success rate for the surface matching is only 35% by using laser scanner
Procedure Step 3: check the stability of the navigation star Head Band
Fixed Star
Total
Less optimized/optimized Surface matching
2
1
3
Good accuracy with error Surface matching
1
7
8
0
0
0
6
6
3
14
17
Good accuracy with error (registration block) Good accuracy Total Test
Surface matching
Problem 2: A head band to stabilize the navigation star is NOT recommended: none of surface matching cases succeeded combined with the head band
- Skull reference base - Châssis de référencement de la base du crâne - Navigation star
Procedure Step 4: Stability of the skull based star (first generation of skull based star) Problem 3: The stars may loose in 92% of cases!!! under the situation: the initial registration with good accuracy Skull based star
%
LOSS of stability of the navigation star during the operation Good accuracy
star loose or not loose but with deviation
23
Registration accuracy remains
2
92%
The stability of the navigation star
Screw remained in skull after removal of the navigation star
self-drilling 1,5 mm diameter screw of 6 mm length
To do’s • 1. improvement of the matching procedure • • • •
Yi Sun’s bite registration block Landmark registration Fiducial marker registration (Surface registration)
• 2. improved fixation of the navigation star • new skull reference base
Improvement of the matching procedure
• By using the registration block Registration points
Indicate the registration points on BrainLab software
Patient was scanned together with registration block by MyRay CBCT 6 registration points were indicated
Check the registration accuracy Dental midline
Incisor edge
Improved matching procedure • By using anatomy points: landmark registration Intra orbital nerve left side Intra orbital nerve right side ANS Tip of 13 Middle of upper incisor Tip of 23
Check the accuracy Dental middle line
Incisor edge
Improved matching procedure
This technique is used in registration for zygomatic implant procedures and yielded in perfect accuracy in 3 cases It necessitates pre-CBCT placement of 4 screws which can be removed after the registration procedure
Head Band
Fixed Star
Total
Less optimized/optimized Surface matching
2
1
3
Good accuracy with error Surface matching
1
7
8
Good accuracy with error (registration block)
0
0
Good accuracy with error (registration block)
0
0
Good accuracy
Surface matching
0
6
6
Anatomy Point
0
17
17
8
8
39
42
Registration block
Total Test
3
The accuracy was judged by the surgeon visually at the beginning of the operation Only the dental middle line and incisor edge was examed for this study Remember: 92% loss of stability of the skull reference base (navigation star) during bimax surgery
Reference screw which is used to check the stability of the navigation star Reference screw at Nasion
Using pointer to check the position of the reference screw in the beginning of the operation
Using pointer to check the position of the reference screw after fixing maxilla
Using pointer to check the position of the reference screw after fixing maxilla
New release of the skull based navigation star • Six patients have been tested with the new released skull based star which holds many improvements • The registration accuracy remained until the end of operation.
Still, the BRAINLAB guidelines can never be met with this device in bimaxillary surgery: page 1/5 BL-IL-521291.Rev.1.0. “Position the device so that it does not hinder the surgeon. The camera must have an unobstructed view of the Skull Reference Array and the registration area at ALL times.”
Conclusion • Customized registration block and anatomy marker based registration could be used for matching from patient to the planning • In this study, only the accuracy of dental middle line and incisor edge were checked. Those points were used to control bi-maxillary surgery results in the traditional way, although the registration accuracy of posterior maxilla is not examined. • By using the new released skull based star, the navigation star could remain firmly in the patient’s head during the whole operation. • At this moment, the Navigation system is not able to control the operation for the mandible yet.