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Oral Maxillofac Surg9:300-308, 2011

Surgical Navigation inCraniomaxillofacial Surgery: ExpensiveToy or Useful Tool? A Classification of

Different IndicationsHeinz-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¶

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he complex 3-dimensional (3D) anatomy and geom-try of the human skull and face combined with theeed for precise symmetry poses challenges for re-onstructive surgery of the region. Therefore, andith the technical improvements during the past 10

ears or so, surgical navigation has become an estab-ished technique in craniomaxillofacial surgery.1-4

Many technical problems have been solved, and theccuracy of multiple strategies of imaging and regis-ration has been proved.5 However, the procedure ofreparing a patient for navigation is still linked toxtra effort for the patient and surgeon. Even nonin-asive registration procedures, such as a splint fixedo the upper jaw, as described by Schramm et al,6

equire dental impressions and additional imagingith the splint in situ.Insecurity surrounds surgical navigation of the

ower jaw with different techniques available, such asounting a dynamic reference frame to the mandi-

*Consultant, Clinic for Cranio-Maxillofacial Surgery, University

ospital, Zurich, Switzerland.

†Consultant, Clinic for Cranio-Maxillofacial Surgery, University


‡Research Fellow, Surgical Planning Laboratory, Harvard Medical

chool, Brigham and Women’s Hospital, Boston, MA.

§Full Professor and Chairman of the Clinic for Cranio-Maxillofa-

ial Surgery, University Hospital, Zurich, Switzerland; Dean of Med-

cal Faculty, University of Zurich, Zurich, Switzerland.

�Consultant, Clinic for Cranio-Maxillofacial Surgery, University


¶Leading Consultant and Vice Chairman, Clinic for Cranio-

axillofacial Surgery, University Hospital, Zurich, Switzerland.

Address correspondence and reprint requests to Dr Lübbers: Clinic

or Cranio-Maxillofacial Surgery, University Hospital, Frauenklin-

kstrasse 24, Zurich 8127 Switzerland; e-mail: [email protected]

2011 American Association of Oral and Maxillofacial Surgeons

278-2391/11/6901-0044$36.00/0

ioi:10.1016/j.joms.2010.07.016

300

le7-9 or retaining the mandible in a defined positiongainst the maxilla.7,10-15 Thus, the state of surgicalavigation of the mandible has been deemed unsatis-actory to date.16

The aim of the present study was to evaluate theeasibility and limitations of surgical navigation. Inddition, we determined the time and effort of theurgical team in relation to the benefit.

aterials and Methods

Surgical procedures performed at the Clinic forranio-Maxillofacial Surgery at the University Hospi-

al, Zurich from 2003 to 2009 in which surgical nav-gation was performed or had been discussed preop-ratively were evaluated for typical patterns. Fourifferent groups of typical clinical situations in the dailyoutines of craniomaxillofacial surgery are presentedTable 1). From these, a classification of the indicationsor surgical navigation was derived (Table 2).

GROUP 1, DIFFICULT RECONSTRUCTION

A patient was referred to our clinic with a history ofn untreated facture of the left zygomatic bone. Thesthetic result was poor, and the need for surgicalevision was indicated. The patient had no functionalymptoms, such as double vision or reduced eye mo-ility. Because a single-sided defect in complex anat-my is the classic situation for preplanning usingirtual mirroring of the healthy side, it was decided tose surgical navigation for this patient. Because thepper jaw was edentulous and because of the needor precise registration over a large surgical field, 6one screws were implanted with the patient under

ocal anesthesia (Fig 1). They were spread over a wideolygon and served as fiducial markers for registra-ion.5 Next, a cone beam computed tomographyCBCT) scan was acquired, which served as a baselineata set for preoperative planning and operative nav-

gation.

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LÜBBERS ET AL 301

The 3D data set was imported into the navigationystem (iPlan ENT, version 2.6; BrainLAB, Feldkirchen,ermany). A semiautomatic threshold segmentation of

he healthy right side was performed and manually op-imized. The resulting 3D object was mirrored to the

Table 1. OVERVIEW OF TYPICAL INDICATIONS FOR SU

Group Example Diagnosis Typical Preparation

1 Secondary correction ofzygomatic bone afteruntreated orinsufficiently treatedtrauma in anedentulous patient

Implantation of bone scwith patient under locanesthesia

Acquisition of new dataVirtual template using

mirroring

2 Acute traumaOrbital floor fracture

with difficulties inidentifying bony edges

Individualization ofprefabricated maxillarsplint

Acquisition of new dataVirtual template using

mirroring3 Foreign body close to

bony structuresLingual displaced root

fragment

Impression and splintconstruction

Acquisition of new dataMarking of root fragmen

4 Bilateral midface fracture Decision against primarylater when orbital flooto be more sufficient

Time estimation determined using cone beam computed to

übbers et al. Surgical Navigation in Craniomaxillofacial Surger

Table 2. CLASSIFICATION OF INDICATIONS FOR SURGI

Class I (Clear Indication)* Class II (L

omplex unilateral orbital wall fracture(eg, missing edges, large extension)

Simple orbital w

omminuted unilateral fracture oflateral midface

Simple fracture

ony tumors with� Bony tumors wExpected difficulties in judging

resection marginsRelevant structures close to tumor

Expected diffiresection m

Relevant struony reconstruction in complex 3D

anatomy�Bony reconstru

anatomy�

oreign bodies in bone� Foreign bodies

Surgical navigation should be performed.†Surgical navigation can be used if no additional procedu‡Indicated in clinical studies with evaluation of (individu§Indicated in extensive technical setup with additional dat�In lower jaw, only if fixation of mandible against max

cquisition and surgical navigation.

übbers et al. Surgical Navigation in Craniomaxillofacial Surgery. J Or

ffected side, and fine positioning was performedanually. Structures not affected by the trauma acted

s a reference (Fig 2). The plan was then discussedith the interdisciplinary surgical team during thereoperative briefing.

L NAVIGATION

Additional Time Needed forNavigation Comments

Screw implantation: 90 minPreoperative planning: 150

min*Surgical navigation: 45 minPostoperative evaluation:

30 min

Situation with maximal timeand effort requiredbecause of edentulousmaxilla and need for highaccuracy over widesurgical field

Good clinical outcome canbe expected

Splint preparation: 20 minPreoperative planning: 90

min*Surgical navigation: 30 minPostoperative evaluation:

15 min

Less time-consumingbecause of smallersurgical field and stabledentition in maxilla

Good clinical outcome canbe expected

Split preparation: 60 minPreoperative planning:

30 minSurgical navigation: 15 minPostoperative

evaluation: NA

More time-consumingbecause of complexdouble-splint technique

Fast planning processGood clinical outcome can

be expectedation (which can be usednstruction of 1 side shownther)

Possibly poor clinicaloutcome

Need for secondarycorrection of 1 orbitalfloor

phy data set; faster with multislice computed tomography.

al Maxillofac Surg 2011.

AVIGATION

Indication)† Class III (No Indication)

ctures Bilateral orbital floor fracture‡

ral midface Bilateral fracture of lateral midface§

Fracture of central midface orlower jaw

�

s in judging the

close to tumor

Soft tissue tumors†

n simple 3D Soft tissue reconstruction

se bony structures� Foreign bodies in soft tissue

e necessary for preparation.) atlas-based virtual reconstruction.operative ultrasonography or magnetic resonance imaging).

same defined position is feasible for preoperative data

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302 SURGICAL NAVIGATION IN CRANIOMAXILLOFACIAL SURGERY

Surgery started with opening the necessary coronalpproach and fixation of the dynamic referencerame, which served to calculate the influence ofamera or patient movements on the registration.andmark checks were done after registration andefore any surgical navigation. The zygomatic bone

IGURE 1. Titanium screws serving as bone-anchored fiducialarkers spread over wide polygon for maximum accuracy in largeeld.

übbers et al. Surgical Navigation in Craniomaxillofacial Sur-ery. J Oral Maxillofac Surg 2011.

FIGURE 2. Healthy side mirrored to


as osteotomized and repositioned according to theurgeon’s clinical judgment and surgical navigation.

Postoperatively, a CBCT data set was acquired, andhe data were fused with the preoperative data setnd the virtual plan using semiautomatic fusion andetermined from the unaffected regions of the bone,

ncluding the right orbit, skull base, and occiput.

GROUP 2, ACUTE TRAUMA

The diagnosis of a severe orbital floor fracture dueo trauma is a regular event. Clinically, enophthalmusombined with double vision in all directions is aypical sign. Eye motility is often reduced. Because ofhe extent of the fracture and the missing bony mar-ins in some areas, a decision was made to use surgi-al navigation.A prefabricated splint with the necessary fiducialarkers for point-to-point registration was individual-

zed using impression material (Fig 3), and a CBCTcan was acquired. Planning was performed by mir-oring the healthy orbit, as described in the previousection (Fig 4).

The reconstruction of the orbital floor was doneith a titanium mesh using a transconjunctival ap-roach, and the position of the mesh was adjustednder the control of the surgical navigation. A post-

d side served as virtual plan (green).
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LÜBBERS ET AL 303

perative CBCT scan was fused with the preoperativeata set and the virtual reconstruction plan (Fig 5).

GROUP 3, FOREIGN BODY

Patients with lingual dislocation of a root segmentfter an attempt at wisdom tooth removal in the right

IGURE 3. Prefabricated splint carrying fiducial markers foroint-to-point registration after individualization with impressionaterial.


FIGURE 4. Virtual reconstruction of orbital floo


andible are often referred to maxillofacial surgeons.ometimes—such as had occurred in the presented ex-mple—an immediate attempt by an oral surgeon toisualize and remove the fragment with the patient un-er local anesthesia fails. In the present case, the patientas then referred to our clinic. The initial CBCT scan

howed the fragment in the mouth floor almost directlyingual to the alveolar socket (Fig 6). Owing to thenown difficulties with foreign body removal and therevious unsuccessful attempt with the patient under

ocal anesthesia, the decision was made to use surgicalavigation with the patient under general anesthesiafter a 3-month interval, which was expected to providexation of the fragment inside the scar tissue. After 3onths, a positioning splint was designed that fixated

he mandible in a defined position against the maxilland included fiducial markers for point-to-point registra-ion (Fig 7). During a short intervention, the fragmentas not visualized but was localized using surgicalavigation (Fig 8) and removed uneventfully. Theostoperative course was also uneventful.

GROUP 4, SEVERE TRAUMA WITHOUT POSSIBILITYOF SURGICAL NAVIGATION

As the main trauma center of the region, mosterious injuries to the facial skeleton are referred to

irroring orbital bone structures of healthy side.
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he University Hospital, Zurich. Multislice CT is regu-arly performed. Our clinic was consulted in the casef severely fragmented and displaced bilateral mid-ace fractures (Fig 9). The orbital walls were affectedn both sides. The initial thought of using surgicalavigation was discarded owing to the lack of healthyone regions to provide a virtual template. However,ecause of an asymmetric result after orbital recon-truction, surgical navigation was performed during aecondary correction in which the clinically satisfac-ory side served as the template. Subsequently, thease proceeded similar to a case such as in group 2.

esults

Within the reviewed cases, the baseline data sethat was used changed over time, shifting from mul-islice CT to CBCT. When threshold segmentationas performed for extraction of the healthy bone

reas, the results using CBCT required more time-onsuming manual, fine work in areas of thin boneeg, the orbital floor and medial wall). First, becausef the imaging technique, the threshold algorithmas less sufficient; and, second, because of the

FIGURE 5. Postoperative evaluation through fusion o


reater resolution of CBCT, more slices had to be s

orked through. The rest of the planning process wasot different.

GROUP 1

The first step of implanting the titanium screws toater serve as fiducial markers was not critical. Therocedure can be performed with the patient under

ocal anesthesia and was performed within about 90inutes. The patients do not feel harmed by it. The

cquisition of a CBCT data set afterward requiredbout 5 minutes.

The 3D data set (Digital Imaging and Communica-ions in Medicine format) was imported into the plan-ing system. The development of a virtual templatesing segmentation of the healthy side and mirroringas uneventful. Manual, fine work was necessary toelineate the orbital walls after segmentation and forne positioning of the mirrored object to its definitiveosition. A maxillofacial resident performed the totallanning process within 150 minutes. The planningocuments were then discussed at a brief meeting ofbout 15 minutes the day before surgery. An addi-ional 25 minutes were needed at the beginning of the

erative plan and postoperative follow-up CBCT scan.


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urgical procedure for system setup (5 minutes), ad-

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itional dressings (5 minutes), and fixation of theynamic reference frame (15 minutes).Before any surgical navigation can occur, the fidu-

ial markers must be exposed and a point-to-pointatching registration process, including meticulous

andmark checks, must be done. This procedure waslso performed by a resident and required about 20inutes. The landmark checks performed during thehole surgical procedure revealed exceptionally high

ccuracy without any measurable discrepancies. Theavigational parts of the surgery took about 20 min-tes altogether. The surgical time saved (eg, becausef better orientation and faster reconstruction) couldot be quantified objectively. However, the surgeonseported better orientation and relevant help for find-ng the correct symmetry during reconstruction usinghe navigation and virtual setup.

The postoperative fusion of the data sets required0 minutes and can be performed by a resident. Thevaluation of the postoperative images was per-ormed in the navigation system and took about 10inutes. A high level of consistency between the

used preoperative plan and postoperative CT data setere seen.Double vision can be expected for about 3 postop-

rative weeks and will subside along with the post-

IGURE 6. Lingual displaced root segment after wisdom toothemoval (detail from CBCT scan).


perative swelling.Lg

GROUP 2

Postoperative CBCT showed high accuracy in theulfillment of the preoperative plan (Fig 5). Clinically,he patient recovered quickly, and, after 2 weeks,hen the main swelling had subsided, no functionalr esthetic impairments were present.The time required for preparation and the actual

urgical navigation was less (Table 1) in the acuteatient group. This was mostly because the 3D situa-ion was easier to assess and the bony edges helped inefining the position of the virtual template.

GROUP 3

Foreign bodies represent a small, but important,ndication for surgical navigation. However, it is veryifficult to predict whether the removal will be sim-le or challenging. The case presented was typical inhat an initial attempt to remove the root fragmentith the patient under local anesthesia failed.Using surgical navigation, foreign body removal be-

omes simpler because marking the foreign object ishe only aspect of the planning procedure. Thus, thelanning time is very short. Also, data import orien-ation and marking the fiducials requires a minimalmount of time (Table 1).

In the presented case, owing to the object’s prox-mity to the mandible, a special splint was required.ts production was fairly time-consuming and re-uired about 60 minutes for the medical staff. Theechnician’s time was in addition to this.

In the presented case, as well as for all other foreignody removal cases, the evaluation of the surgicalavigation revealed it to be fast and successful.

IGURE 7. Individual splint for positioning mandible against max-lla for preoperative data acquisition and surgical navigation (in-luding fiducial markers for point-to-point registration).


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GROUP 4

Group 4 represents patients who were initiallyonsidered for surgical navigation but for whom itas not indicated for various reasons. Two main

easons were identified. First, immediate interven-ion was often necessary, with the lack of timevailable for preparing the surgical navigation. Sec-nd—and much more often—the patient presentedith bilateral trauma, which would not allow theirroring of a healthy side. In these circumstances,

he additional effort required for surgical naviga-ion would often be useless because of the lackf benefit.

iscussion

The baseline data set changed during the study periodrom CT to CBCT. This was supported by the publishedata.17 CBCT requires lower radiation doses than CT18

nd provides high-resolution bone imaging but not soft

FIGURE 8. Localization of roo


issue differentiation.19 These differences are basically i

rrelevant for surgical navigation because the bony struc-ures are required for the navigation in the vast majorityf cases. The preparation of the virtual object from theealthy bone structures will require more time ifBCT is used to provide the 3D data set. However,

his difference only occurred if a “nice” virtual tem-late was the goal. “Sloppy” manual, fine work will

ead to objects with small holes; however, in ourxperience, the surgical navigation was not influ-nced by this difference.The registration technique used is a key element in

he precision of surgical navigation.20 If pre-existingata sets must be used, either anatomic landmarkegistration or laser surface matching are the methodsf choice.5,21 Because laser surface matching isnown to be more accurate, it should be the pre-erred technique.5,22-24 Landmark registration coulderve as a backup.

Groups 1 and 2 represent the classic indications forurgical navigation and have been reported by several

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LÜBBERS ET AL 307

een indicated by many investigators as suitable forurgical navigation.12,13,16,25

In group 4, a case of bilateral fracture interferedith the extraction of a virtual template from aealthy region. Prototype concepts have been pre-ented that use a bone atlas—similar to a brain atlasnd described by different investigators26,27—with in-ividual size and form adjustment as a solution inonstructing a virtual template. However, this tech-ique must be validated in clinical studies beforeeing accepted into routine use. Therefore, atresent, we have classified bilateral fracture as unsuit-ble for surgical navigation (Table 2). However, just asccurred in the presented patient, after initial recon-truction, there might be room for improvement, andhis is when surgical navigation could be useful.

Finally, the total time invested by the surgical teamreoperatively (Table 1) was very acceptable. Regard-

ng the preoperative briefing time spent, we wouldecommend a briefing for the surgical team. We be-ieve the time spent for actual navigation during sur-ery to be more or less compensated by the timeaved owing to better orientation and the quickerssessment of the reconstruction symmetry.

An overview of our classification for the indicationsf surgical navigation is given in Table 2.Using the described classification, we have recom-

IGURE 9. Bilateral midface and orbital wall fracture withoutealthy side to serve as virtual template.


ended surgical navigation for all Class 1 indications,

ccording to Table 2. For Class 2 indications, surgicalavigation makes sense if no additional harm to theatient will result with respect to the radiation doser any invasive procedures. In these situations, limi-ations exist but can be managed. Class 3 situations doot provide any room for surgical navigation. Surgicalavigation in the area of the mandible requires metic-lous planning but is not contraindicated per se.We believe that, especially in a growing organism,

urgical navigation is a promising concept for achiev-ng accurate reconstruction without alloplastic mate-ial, thus avoiding secondary reconstructive surgery.

cknowledgments

The authors wish to acknowledge Jörg Achinger of BrainLAB foris great support in all technical questions regarding the navigationystem and would like to thank Hildegard Eschle, senior librarian ofhe University Zurich Dental School for helping with the dataesearch.

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