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

Navigation star

(skull reference base)

Pointer

+ SOFTWARE

preoperative procedure

check of the accuracy with the Z-touch

Peroperative procedure

step 1: fixation of the navigation star on patients head

HEAD BAND

SKULL BASED STAR :

fixation screw

Procedure

Step 2: matching the patient to the CBCT image

Laser scanner was

used to sample the

surface of patient's

face

SURFACE LASER SCANNING

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

Good accuracy Surface matching 0 6 6

Total Test 3 14 17

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

Good accuracy with error

(registration block)

0 0

Good accuracy Surface matching 0 6 6

Total Test 3 14 17

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 stabilityof the navigation

star during the operation

Good accuracy star loose

or not loose but with deviation

23 92%

Registration accuracy

remains

2

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 accuracyDental 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

Registration block 8 8

Total Test 3 39 42

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.