Surgical navigation

J Oral Maxillofac Surg
69:300-308, 2011

Surgical Navigation in
Craniomaxillofacial Surgery: Expensive
Toy or Useful Tool? A Classification of
Different Indications
Heinz-Theo Lübbers, MD, DMD,*
Christine Jacobsen, MD, DMD,† Felix Matthews, MD, MBA,‡
Klaus W. Grätz, MD, DMD,§ Astrid Kruse, MD, DMD, and
Joachim A. Obwegeser, MD, DMD¶

The complex 3-dimensional (3D) anatomy and geom- ble7-9 or retaining the mandible in a defined position
etry of the human skull and face combined with the against the maxilla.7,10-15 Thus, the state of surgical
need for precise symmetry poses challenges for re- navigation of the mandible has been deemed unsatis-
constructive surgery of the region. Therefore, and factory to date.16
with the technical improvements during the past 10 The aim of the present study was to evaluate the
years or so, surgical navigation has become an estab- feasibility and limitations of surgical navigation. In
lished technique in craniomaxillofacial surgery.1-4 addition, we determined the time and effort of the
Many technical problems have been solved, and the surgical team in relation to the benefit.
accuracy of multiple strategies of imaging and regis-
tration has been proved.5 However, the procedure of Materials and Methods
preparing a patient for navigation is still linked to
extra effort for the patient and surgeon. Even nonin- Surgical procedures performed at the Clinic for
vasive registration procedures, such as a splint fixed Cranio-Maxillofacial Surgery at the University Hospi-
to the upper jaw, as described by Schramm et al,6 tal, Zurich from 2003 to 2009 in which surgical nav-
require dental impressions and additional imaging igation was performed or had been discussed preop-
with the splint in situ. eratively were evaluated for typical patterns. Four
Insecurity surrounds surgical navigation of the different groups of typical clinical situations in the daily
lower jaw with different techniques available, such as routines of craniomaxillofacial surgery are presented
mounting a dynamic reference frame to the mandi- (Table 1). From these, a classification of the indications
for surgical navigation was derived (Table 2).

*Consultant, Clinic for Cranio-Maxillofacial Surgery, University GROUP 1, DIFFICULT RECONSTRUCTION
Hospital, Zurich, Switzerland. A patient was referred to our clinic with a history of
†Consultant, Clinic for Cranio-Maxillofacial Surgery, University an untreated facture of the left zygomatic bone. The
Hospital, Zurich, Switzerland. esthetic result was poor, and the need for surgical
‡Research Fellow, Surgical Planning Laboratory, Harvard Medical revision was indicated. The patient had no functional
School, Brigham and Women’s Hospital, Boston, MA. symptoms, such as double vision or reduced eye mo-
§Full Professor and Chairman of the Clinic for Cranio-Maxillofa- tility. Because a single-sided defect in complex anat-
cial Surgery, University Hospital, Zurich, Switzerland; Dean of Med- omy is the classic situation for preplanning using
ical Faculty, University of Zurich, Zurich, Switzerland. virtual mirroring of the healthy side, it was decided to
Consultant, Clinic for Cranio-Maxillofacial Surgery, University use surgical navigation for this patient. Because the
Hospital, Zurich, Switzerland. upper jaw was edentulous and because of the need
¶Leading Consultant and Vice Chairman, Clinic for Cranio- for precise registration over a large surgical field, 6
Maxillofacial Surgery, University Hospital, Zurich, Switzerland. bone screws were implanted with the patient under
Address correspondence and reprint requests to Dr Lübbers: Clinic local anesthesia (Fig 1). They were spread over a wide
for Cranio-Maxillofacial Surgery, University Hospital, Frauenklin- polygon and served as fiducial markers for registra-
ikstrasse 24, Zurich 8127 Switzerland; e-mail: t.luebbers@gmail.com tion.5 Next, a cone beam computed tomography
© 2011 American Association of Oral and Maxillofacial Surgeons (CBCT) scan was acquired, which served as a baseline
0278-2391/11/6901-0044$36.00/0 data set for preoperative planning and operative nav-
doi:10.1016/j.joms.2010.07.016 igation.

300

LÜBBERS ET AL 301

Table 1. OVERVIEW OF TYPICAL INDICATIONS FOR SURGICAL NAVIGATION

Additional Time Needed for
Group Example Diagnosis Typical Preparation Navigation Comments

1 Secondary correction of Implantation of bone screwsScrew implantation: 90 min Situation with maximal time
zygomatic bone after with patient under local Preoperative planning: 150 and effort required
untreated or anesthesia min* because of edentulous
insufficiently treated Acquisition of new data setSurgical navigation: 45 min maxilla and need for high
trauma in an Virtual template using Postoperative evaluation: accuracy over wide
edentulous patient mirroring 30 min surgical field
Good clinical outcome can
be expected
2 Acute trauma Individualization of Splint preparation: 20 min Less time-consuming
Orbital floor fracture prefabricated maxillary Preoperative planning: 90 because of smaller
with difficulties in splint min* surgical field and stable
identifying bony edges Acquisition of new data set Surgical navigation: 30 min dentition in maxilla
Virtual template using Postoperative evaluation: Good clinical outcome can
mirroring 15 min be expected
3 Foreign body close to Impression and splint Split preparation: 60 min More time-consuming
bony structures construction Preoperative planning: because of complex
Lingual displaced root Acquisition of new data set 30 min double-splint technique
fragment Marking of root fragment Surgical navigation: 15 min Fast planning process
Postoperative Good clinical outcome can
evaluation: NA be expected
4 Bilateral midface fracture Decision against primary navigation (which can be used Possibly poor clinical
later when orbital floor reconstruction of 1 side shown outcome
to be more sufficient than other) Need for secondary
correction of 1 orbital
floor
*Time estimation determined using cone beam computed tomography data set; faster with multislice computed tomography.
Lübbers et al. Surgical Navigation in Craniomaxillofacial Surgery. J Oral Maxillofac Surg 2011.

The 3D data set was imported into the navigation affected side, and fine positioning was performed
system (iPlan ENT, version 2.6; BrainLAB, Feldkirchen, manually. Structures not affected by the trauma acted
Germany). A semiautomatic threshold segmentation of as a reference (Fig 2). The plan was then discussed
the healthy right side was performed and manually op- with the interdisciplinary surgical team during the
timized. The resulting 3D object was mirrored to the preoperative briefing.

Table 2. CLASSIFICATION OF INDICATIONS FOR SURGICAL NAVIGATION

Class I (Clear Indication)* Class II (Limited Indication)† Class III (No Indication)

Complex unilateral orbital wall fracture Simple orbital wall fractures Bilateral orbital floor fracture‡
(eg, missing edges, large extension)
Comminuted unilateral fracture of Simple fracture of lateral midface Bilateral fracture of lateral midface§
lateral midface Fracture of central midface or
lower jaw
Bony tumors with Bony tumors without
Expected difficulties in judging Expected difficulties in judging the Soft tissue tumors†
resection margins resection margins
Relevant structures close to tumor Relevant structures close to tumor
Bony reconstruction in complex 3D Bony reconstruction in simple 3D Soft tissue reconstruction
anatomy anatomy
Foreign bodies in bone Foreign bodies in close bony structures Foreign bodies in soft tissue
*Surgical navigation should be performed.
†Surgical navigation can be used if no additional procedures are necessary for preparation.
‡Indicated in clinical studies with evaluation of (individualized) atlas-based virtual reconstruction.
§Indicated in extensive technical setup with additional data (eg, operative ultrasonography or magnetic resonance imaging).
In lower jaw, only if fixation of mandible against maxilla in same defined position is feasible for preoperative data
acquisition and surgical navigation.

302 SURGICAL NAVIGATION IN CRANIOMAXILLOFACIAL SURGERY

was osteotomized and repositioned according to the
surgeon’s clinical judgment and surgical navigation.
Postoperatively, a CBCT data set was acquired, and
the data were fused with the preoperative data set
and the virtual plan using semiautomatic fusion and
determined from the unaffected regions of the bone,
including the right orbit, skull base, and occiput.
GROUP 2, ACUTE TRAUMA
The diagnosis of a severe orbital floor fracture due
to trauma is a regular event. Clinically, enophthalmus
combined with double vision in all directions is a
typical sign. Eye motility is often reduced. Because of
the extent of the fracture and the missing bony mar-
FIGURE 1. Titanium screws serving as bone-anchored fiducial
markers spread over wide polygon for maximum accuracy in large gins in some areas, a decision was made to use surgi-
field. cal navigation.
Lübbers et al. Surgical Navigation in Craniomaxillofacial Sur- A prefabricated splint with the necessary fiducial
gery. J Oral Maxillofac Surg 2011. markers for point-to-point registration was individual-
ized using impression material (Fig 3), and a CBCT
scan was acquired. Planning was performed by mir-
Surgery started with opening the necessary coronal roring the healthy orbit, as described in the previous
approach and fixation of the dynamic reference section (Fig 4).
frame, which served to calculate the influence of The reconstruction of the orbital floor was done
camera or patient movements on the registration. with a titanium mesh using a transconjunctival ap-
Landmark checks were done after registration and proach, and the position of the mesh was adjusted
before any surgical navigation. The zygomatic bone under the control of the surgical navigation. A post-

FIGURE 2. Healthy side mirrored to affected side served as virtual plan (green).

LÜBBERS ET AL 303

mandible are often referred to maxillofacial surgeons.
Sometimes—such as had occurred in the presented ex-
ample—an immediate attempt by an oral surgeon to
visualize and remove the fragment with the patient un-
der local anesthesia fails. In the present case, the patient
was then referred to our clinic. The initial CBCT scan
showed the fragment in the mouth floor almost directly
lingual to the alveolar socket (Fig 6). Owing to the
known difficulties with foreign body removal and the
previous unsuccessful attempt with the patient under
local anesthesia, the decision was made to use surgical
navigation with the patient under general anesthesia
after a 3-month interval, which was expected to provide
fixation of the fragment inside the scar tissue. After 3
FIGURE 3. Prefabricated splint carrying fiducial markers for months, a positioning splint was designed that fixated
point-to-point registration after individualization with impression
material.
the mandible in a defined position against the maxilla
and included fiducial markers for point-to-point registra-
Lübbers et al. Surgical Navigation in Craniomaxillofacial Sur-
gery. J Oral Maxillofac Surg 2011. tion (Fig 7). During a short intervention, the fragment
was not visualized but was localized using surgical
navigation (Fig 8) and removed uneventfully. The
operative CBCT scan was fused with the preoperative postoperative course was also uneventful.
data set and the virtual reconstruction plan (Fig 5).
GROUP 4, SEVERE TRAUMA WITHOUT POSSIBILITY
GROUP 3, FOREIGN BODY OF SURGICAL NAVIGATION
Patients with lingual dislocation of a root segment As the main trauma center of the region, most
after an attempt at wisdom tooth removal in the right serious injuries to the facial skeleton are referred to

FIGURE 4. Virtual reconstruction of orbital floor by mirroring orbital bone structures of healthy side.


FIGURE 5. Postoperative evaluation through fusion of preoperative plan and postoperative follow-up CBCT scan.

the University Hospital, Zurich. Multislice CT is regu- worked through. The rest of the planning process was
larly performed. Our clinic was consulted in the case not different.
of severely fragmented and displaced bilateral mid-
face fractures (Fig 9). The orbital walls were affected GROUP 1
on both sides. The initial thought of using surgical
navigation was discarded owing to the lack of healthy The first step of implanting the titanium screws to
bone regions to provide a virtual template. However, later serve as fiducial markers was not critical. The
because of an asymmetric result after orbital recon- procedure can be performed with the patient under
struction, surgical navigation was performed during a local anesthesia and was performed within about 90
secondary correction in which the clinically satisfac- minutes. The patients do not feel harmed by it. The
tory side served as the template. Subsequently, the acquisition of a CBCT data set afterward required
case proceeded similar to a case such as in group 2. about 5 minutes.
The 3D data set (Digital Imaging and Communica-
tions in Medicine format) was imported into the plan-
Results ning system. The development of a virtual template
Within the reviewed cases, the baseline data set using segmentation of the healthy side and mirroring
that was used changed over time, shifting from mul- was uneventful. Manual, fine work was necessary to
tislice CT to CBCT. When threshold segmentation delineate the orbital walls after segmentation and for
was performed for extraction of the healthy bone fine positioning of the mirrored object to its definitive
areas, the results using CBCT required more time- position. A maxillofacial resident performed the total
consuming manual, fine work in areas of thin bone planning process within 150 minutes. The planning
(eg, the orbital floor and medial wall). First, because documents were then discussed at a brief meeting of
of the imaging technique, the threshold algorithm about 15 minutes the day before surgery. An addi-
was less sufficient; and, second, because of the tional 25 minutes were needed at the beginning of the
greater resolution of CBCT, more slices had to be surgical procedure for system setup (5 minutes), ad-

LÜBBERS ET AL 305

GROUP 2
Postoperative CBCT showed high accuracy in the
fulfillment of the preoperative plan (Fig 5). Clinically,
the patient recovered quickly, and, after 2 weeks,
when the main swelling had subsided, no functional
or esthetic impairments were present.
The time required for preparation and the actual
surgical navigation was less (Table 1) in the acute
patient group. This was mostly because the 3D situa-
tion was easier to assess and the bony edges helped in
defining the position of the virtual template.

GROUP 3
Foreign bodies represent a small, but important,
indication for surgical navigation. However, it is very
difficult to predict whether the removal will be sim-
ple or challenging. The case presented was typical in
that an initial attempt to remove the root fragment
with the patient under local anesthesia failed.
Using surgical navigation, foreign body removal be-
comes simpler because marking the foreign object is
the only aspect of the planning procedure. Thus, the
planning time is very short. Also, data import orien-
tation and marking the fiducials requires a minimal
FIGURE 6. Lingual displaced root segment after wisdom tooth
removal (detail from CBCT scan).
amount of time (Table 1).
In the presented case, owing to the object’s prox-
Lübbers et al. Surgical Navigation in Craniomaxillofacial Sur-
gery. J Oral Maxillofac Surg 2011. imity to the mandible, a special splint was required.
Its production was fairly time-consuming and re-
quired about 60 minutes for the medical staff. The
ditional dressings (5 minutes), and fixation of the technician’s time was in addition to this.
dynamic reference frame (15 minutes). In the presented case, as well as for all other foreign
Before any surgical navigation can occur, the fidu- body removal cases, the evaluation of the surgical
cial markers must be exposed and a point-to-point navigation revealed it to be fast and successful.
matching registration process, including meticulous
landmark checks, must be done. This procedure was
also performed by a resident and required about 20
minutes. The landmark checks performed during the
whole surgical procedure revealed exceptionally high
accuracy without any measurable discrepancies. The
navigational parts of the surgery took about 20 min-
utes altogether. The surgical time saved (eg, because
of better orientation and faster reconstruction) could
not be quantified objectively. However, the surgeons
reported better orientation and relevant help for find-
ing the correct symmetry during reconstruction using
the navigation and virtual setup.
The postoperative fusion of the data sets required
20 minutes and can be performed by a resident. The
evaluation of the postoperative images was per-
formed in the navigation system and took about 10
minutes. A high level of consistency between the
fused preoperative plan and postoperative CT data set
FIGURE 7. Individual splint for positioning mandible against max-
were seen. illa for preoperative data acquisition and surgical navigation (in-
Double vision can be expected for about 3 postop- cluding fiducial markers for point-to-point registration).
erative weeks and will subside along with the post- Lübbers et al. Surgical Navigation in Craniomaxillofacial Sur-
operative swelling. gery. J Oral Maxillofac Surg 2011.


FIGURE 8. Localization of root fragment without open visualization.

GROUP 4 irrelevant for surgical navigation because the bony struc-
Group 4 represents patients who were initially tures are required for the navigation in the vast majority
considered for surgical navigation but for whom it of cases. The preparation of the virtual object from the
was not indicated for various reasons. Two main healthy bone structures will require more time if
reasons were identified. First, immediate interven- CBCT is used to provide the 3D data set. However,
tion was often necessary, with the lack of time this difference only occurred if a “nice” virtual tem-
available for preparing the surgical navigation. Sec- plate was the goal. “Sloppy” manual, fine work will
ond—and much more often—the patient presented lead to objects with small holes; however, in our
with bilateral trauma, which would not allow the experience, the surgical navigation was not influ-
mirroring of a healthy side. In these circumstances, enced by this difference.
the additional effort required for surgical naviga- The registration technique used is a key element in
tion would often be useless because of the lack the precision of surgical navigation.20 If pre-existing
of benefit. data sets must be used, either anatomic landmark
registration or laser surface matching are the methods
of choice.5,21 Because laser surface matching is
Discussion
known to be more accurate, it should be the pre-
The baseline data set changed during the study period ferred technique.5,22-24 Landmark registration could
from CT to CBCT. This was supported by the published serve as a backup.
data.17 CBCT requires lower radiation doses than CT18 Groups 1 and 2 represent the classic indications for
and provides high-resolution bone imaging but not soft surgical navigation and have been reported by several
tissue differentiation.19 These differences are basically investigators.2,4 Foreign bodies (group 3) have also

LÜBBERS ET AL 307

according to Table 2. For Class 2 indications, surgical
navigation makes sense if no additional harm to the
patient will result with respect to the radiation dose
or any invasive procedures. In these situations, limi-
tations exist but can be managed. Class 3 situations do
not provide any room for surgical navigation. Surgical
navigation in the area of the mandible requires metic-
ulous planning but is not contraindicated per se.
We believe that, especially in a growing organism,
surgical navigation is a promising concept for achiev-
ing accurate reconstruction without alloplastic mate-
rial, thus avoiding secondary reconstructive surgery.
Acknowledgments
The authors wish to acknowledge Jörg Achinger of BrainLAB for
his great support in all technical questions regarding the navigation
system and would like to thank Hildegard Eschle, senior librarian of
the University Zurich Dental School for helping with the data
research.

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