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Journal of Cranio-Maxillo-Facial Surgery xxx (2014) 1e7

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Journal of Cranio-Maxillo-Facial Surgery

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Stereolithographic skull models in the surgical planning of fronto-supraorbital bar advancement for non-syndromic trigonocephaly

D.P.F. van Nunen a,*, L.E. Janssen a, B.M. Stubenitsky a, K.S. Han b, M.S.M. Muradin c,*

aDepartment of Plastic and Reconstructive Surgery (Head: M. Kon), University of Utrecht Medical Center, Heidelberglaan 100,PO Box 85500, 3508 GA Utrecht, The NetherlandsbDepartment of Neurosurgery (Head: L.P.E. Regli), University of Utrecht Medical Center, Heidelberglaan 100, PO Box 85500, 3508 GA Utrecht,The NetherlandscDepartment of Oral-Maxillofacial Surgery (Head: R. Koole), University of Utrecht Medical Center, Heidelberglaan 100, PO Box 85500, 3508 GA Utrecht,The Netherlands

a r t i c l e i n f o

Article history:Paper received 25 August 2013Accepted 3 January 2014

Keywords:[MeSH]CraniosynostosesTrigonocephalyMetopic synostosisImagingThree-dimensional

* Corresponding authors. Department of Oral-MaxilUtrecht Medical Center, Heidelberglaan 100, PO BoxNetherlands. Tel.: þ31 88 77 57751; fax: þ31 88 75 5

E-mail addresses: d.p.f.vannunen@gmail.com (D.P.F.gmail.com (M.S.M. Muradin).

1010-5182/$ e see front matter � 2014 European Asshttp://dx.doi.org/10.1016/j.jcms.2014.01.017

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a b s t r a c t

Background: Fronto-supraorbital bar advancement in the treatment for trigonocephaly is associated withextensive intraoperative blood loss and compensatory erythrocyte transfusions. Since both are related tothe length of surgery, efforts have been focused on optimizing preoperative preparations. The utilizationof three-dimensional skull models in surgical planning allows for familiarization with the patient’sanatomy, the optimization of osteotomies, the preparation of bone grafts and the selection of fixationplates.Methods: Stereolithographic skull models were used in the surgical planning for five patients with non-syndromic trigonocephaly treated in Wilhelmina Children’s Hospital in 2012. A comparison group wascomposed of six patients with non-syndromic trigonocephaly treated by the same surgical team. Once allpatients had received surgery, a retrospective chart review was performed to identify the volumes ofperioperative blood loss and erythrocyte transfusions and the length of the procedure. Furthermore, theeducational value of the models was assessed in a round table discussion with the surgical team andresidents.Results: In the model group patients were transfused a mean 24 ml/kg (27% of Estimated Blood Volume[EBV]) compared to 16 ml/kg (18% of EBV) in the comparison group (P ¼ 0.359) for a mean perioperativeblood loss of 53 ml/kg (60% of EBV) in the model group against 40 ml/kg (41% of EBV) in the comparisongroup (P ¼ 0.792). The mean length of surgery in the model groups was 256 min versus 252 min in thecomparison group (P ¼ 0.995). Evaluation of educational purposes demonstrated that the models had arole in the instruction of residents and communication to parents, but did not improve the insight ofexperienced surgeons.Conclusion: The usage of stereolithographic skull models in the treatment of non-syndromic trig-onocephaly does not reduce the mean volume of perioperative erythrocyte transfusions, the meanvolume of perioperative blood loss nor the mean length of the surgical procedure. Nonetheless, themodels do facilitate the education of the patient’s parents as well as support the training of residents.

� 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rightsreserved.

1. Introduction

Trigonocephaly is a craniosynostosis characterized by a wedge-shaped forehead with a midline ridge due to restricted transverse

lofacial Surgery, University of85500, 3508 GA Utrecht, The5504.vanNunen),marvickmuradin@

ociation for Cranio-Maxillo-Facial

en DPF, et al., Stereolithographaly, Journal of Cranio-Maxi

growth of the skull following premature fusion and ossification ofthe metopic suture (Panchal and Uttchin, 2003; van der Meulen,2012). Although the severity of the phenotype demonstrates asignificant variation amongst patients, there is often a degree ofbitemporal indentation and supraorbital retrusion, magnified bydeficient development of the lateral orbital rims. In addition,hypotelorism of the medial orbital walls and epicanthal folds areoften present (van der Meulen, 2012). Trigonocephaly occurs in1:700 to 1:15,000 newborn children (Alderman et al., 1997;Lajeunie et al., 1998; Kweldam et al., 2011) and is associated with

Surgery. Published by Elsevier Ltd. All rights reserved.

hic skull models in the surgical planning of fronto-supraorbital barllo-Facial Surgery (2014), http://dx.doi.org/10.1016/j.jcms.2014.01.017

Table 1Estimated blood loss according to Kearney et al. (1989).

Step Mathematical formula

1 Estimated Blood Volume (EBV, ml) ¼ weight (kg) � 80 ml/kg(children < 12 months of age)Estimated Blood Volume (EBV, ml) ¼ weight (kg) � 75 ml/kg(children � 12 months of age)

2 Estimated Red Cell Mass (ERCM, ml) ¼ EBV � Haematocrit (l/l)Haematocrit of packed erythrocytes at WCH ¼ 0.60 l/l

3 ERCMlost ¼ ERCMpreoperative þ ERCMtransfused � ERCMpostoperative

4 Estimated Blood Loss (EBL, ml) ¼ ERCMlost/Haematocritpreoperative

D.P.F. van Nunen et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2014) 1e72

a syndrome in 35% of patients (Lajeunie et al., 1998). Delays inneuropsychological development have been reported for 15e62% ofpatients (Oi and Matsumoto, 1987; Sidoti et al., 1996; Aryan et al.,2005; Engel et al., 2012). The aetiology of metopic synostosis re-mains unknown (Engel et al., 2012; van der Meulen, 2012), but it isoften ascribed to either an intrinsic malformation of the frontalbones (Lajeunie et al., 1998; Rasmussen et al., 2007; Wilkie et al.2007; Senarath-Yapa et al. 2012) fetal head constraints in the pel-vic area during pregnancy (Graham and Smith, 1980; Smartt et al.,2005) or to a malformation of the frontal lobes leading to areduction of stimuli for cranial growth (Moss, 1959; Senarath-Yapaet al. 2012). Surgical intervention is warranted in order to increasethe volume of the underdeveloped anterior cranial fossa as well asto improve aesthetics (Panchal and Uttchin, 2003; Forrest andHopper, 2013).

Since the publication of the classic papers by Hoffman andMohr(1976) and Marchac (1978) surgical techniques involvingadvancement of the fronto-supraorbital bar with remodelling ofthe frontal bone have become the standard in the treatment oftrigonocephaly. Disadvantages of these procedures are the exten-sive amount of intraoperative blood loss and associated transfusionrates (Stricker et al., 2010), both of which are correlated to theduration of surgery (White et al., 2009; van Uitert et al., 2011). Ef-forts to reduce the length of corrective surgery have been partiallyfocused on enhancing preoperative preparations. One approach hasbeen the use of three-dimensional physical models in surgicalplanning, which allows for familiarization with the patient’s anat-omy, the optimization of osteotomies, the preparation of bonegrafts and the selection of fixation plates (D’Urso et al., 1998; Saileret al., 1998; Sannomiya et al., 2006; Sinn et al., 2006).

The objective of the present study is to evaluate the use of three-dimensional stereolithographic models in the surgical treatmentfor trigonocephaly with regards to its effect on the volumes ofblood loss, transfusion requirements and length of the surgicalprocedure.

2. Material and methods

In order to evaluate the added value of three-dimensional solidmodels in the treatment protocol for non-syndromic trig-onocephaly, stereolithographic models were ordered for a series offive consecutive patients referred to the Craniofacial Centre of theWilhelmina Children’s Hospital in 2012. The comparison groupconsisted of all prior patients with non-syndromic trigonocephalytreated by the same surgical team, which took its current form inmid-2009. Once all patients in the model group had receivedcorrective surgery, a retrospective chart review was conducted forboth groups inwhich the following characteristicswere recorded foreach patient: demographics, past medical history, prescriptiondrugs, duration of the surgical procedure, reported blood loss duringsurgery and the volumes of packed erythrocytes transfused in theperi- and postoperative periods. The retrospective chart reviewwasapproved beforehand by the local Medical Ethics Committee.

Given the inherent difficulty of accurately measuring perioper-ative blood loss in craniosynostosis surgery (Stricker et al., 2010;Goobie et al. 2011), a second estimate of the perioperative bloodloss was calculated following the methodology of Kearney et al.(1989) (Table 1). The duration of the surgical procedure wasdefined as the timespan between the start of surgical preparationsafter induction of general anaesthesia and the end of surgicalwound closure.

The primary endpoint of this study was the volume of allogeneicerythrocyte transfusion in the peri- and postoperative periods.Secondary endpoints were the estimated volume of blood loss andthe duration of the surgical procedure. Statistical analysis was

Please cite this article in press as: van Nunen DPF, et al., Stereolithograpadvancement for non-syndromic trigonocephaly, Journal of Cranio-Maxi

performed with IBM SPSS Statistics 20.0 (IBM Inc, New York, NY,USA) using the ManneWhitney U-test. A P-value of less than 0.05was considered statistically significant.

2.1. Stereolithographic models e Production and employment

After their first visit to the outpatient clinic of the CraniofacialCentre ofWCH all patients in this study underwent a helical volumeCT-scan of the cranium following the standard diagnostic protocol.The CT-scans were performed at a gantry tilt of 0�, a tube current of100 mA at 90 kV and with a slice thickness of 1 mm. The scan dataof the model group were transferred to Materialise N.V. (Leuven,Belgium) and uploaded into the proprietary surgical planningsoftware package Synthes ProPlan CMF (Synthes Holding AG,Solothurn, Switzerland). During an interactive online planningsession the operationwas simulated on a virtual three-dimensionalreconstruction of the skull following the directions of the surgicalteam (Fig. 1). The desired postoperative result was converted to theSTL-file format accepted by the stereolithography three-dimensional printers. The production of the models started witha bath filled with a liquid UV-sensitive resin in which an immersedplatformwas raised to a level just below the surface. Subsequently,the stereolithography printer guided a heliumecadmium laserbeam over the surface polymerizing the resin and constructing theinitial layer of the model. The platform with the initial layer wasthen slightly lowered allowing the laser beam to create the secondlayer. This process was then repeated until all layers of the modelwere formed. Next, the model was removed from the bath andexcess resin and support struts were cleared by hand. In the finalstep the model was placed in a UV-oven which increased thestrength of the model by completing the process of photo-polymerization and cross-linking of the resin.

For each patient in the model group two distinct skull modelswere ordered: one of the preoperative situation (Fig. 2) and one ofthe desired postoperative situation (Fig. 3). Delivery of the modelsto theWCH required fivework days after the order was placed withMaterialize N.V. The costs per individual skull model amounted toV 900 e and were covered by the patients’ health insurance plans.During the preoperative period the three-dimensionalmodels wereused to explain the proposed surgical technique to the patients’parents as well as to residents in oral and maxillofacial surgery,plastic surgery and neurosurgery. Furthermore, after sterilizationthemodels were brought into theatre on the day of surgery to allowfor quick intraoperative evaluation of the patients’ cranial anatomyand surgical plan.

3. Results

The five patients in the model group were all males, on averageten months of age at the date of surgery with a body weight of9.2 kg (Table 2). The comparison group consisted of six patients, ofwhich three were females, who received surgery at a mean age of12.3 months weighing a mean 10.2 kg. No patient in either group

hic skull models in the surgical planning of fronto-supraorbital barllo-Facial Surgery (2014), http://dx.doi.org/10.1016/j.jcms.2014.01.017

Fig. 1. Surgical planning.

D.P.F. van Nunen et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2014) 1e7 3

had a history of cardiopulmonary or haematologic disease. Pre-scription drugs influencing the coagulation process were not takenby any patient in the preoperative period. All trigonocephaly pa-tients were treated by fronto-supraorbital advancement andremodelling in an open procedure. Haemostasis was performed

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using bipolar electrocoagulation, bone wax and, in all patients, bythe administration of tranexamic acid during surgery.

The mean reported perioperative blood loss in the model groupwas 29 ml/kg (or 33% of Estimated Blood Volume [EBV]) with arange of 23e42 ml/kg (28e43% of EBV), see Table 2. Patients in the

hic skull models in the surgical planning of fronto-supraorbital barllo-Facial Surgery (2014), http://dx.doi.org/10.1016/j.jcms.2014.01.017

Fig. 2. Stereolithographic skull model e preoperative situation.

D.P.F. van Nunen et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2014) 1e74

comparison group reportedly lost a mean 22 ml/kg of blood (25% ofEBV) varying between 8 and 41 ml/kg (7e46% of EBV). Followingthemethod by Kearney et al. the perioperative blood loss amountedto amean 53ml/kg (60% of EBV) with a range of 33e100ml/kg (33e111% of EBV) in the model group and up to a mean of 40 ml/kg (or41% of EBV) in the comparison group, ranging from 17 to 58 ml/kg(18e58% of EBV).

During surgery the patients in the model group were adminis-tered between 14 and 54 ml/kg of allogeneic erythrocyte

Fig. 3. Stereolithographic skull model

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transfusions (17e55% of EBV) with a mean of 24 ml/kg (or 27% ofEBV). In the comparison group patients received a mean 16 ml/kg(or 18% of EBV) of allogeneic erythrocytes with a range of 10e30ml/kg (9e34% of EBV). In the postoperative period no additionalerythrocyte transfusions were given to any patient. Autologouserythrocyte transfusions were not used. No transfusion reactionswere observed.

In the model group the surgical procedure required a mean timeof 256 min (range: 228e290 min), compared to a mean 252 min in

e desired preoperative situation.

hic skull models in the surgical planning of fronto-supraorbital barllo-Facial Surgery (2014), http://dx.doi.org/10.1016/j.jcms.2014.01.017

Table 2Results.

Subject Gender(M/F)

Age(months)

Weight(kg)

Estimated blood loss Erythrocyte transfusion Duration ofsurgery (min)

Reported Kearney-method

To tal (ml) ml/kg % EBV Total (ml) ml/kg % EBV Total (ml) ml/kg % EBV

Non-model group1 M 14 10.9 200 18 19% 609 58 58% 250 23 24% 2582 M 12 10.6 300 28 33% 405 41 45% 100 10 11% 3103 F 11 9.9 404 41 46% 480 51 55% 300 30 34% 1814 M 11 9.8 225 23 26% 160 17 18% 100 10 11% 2395 F 15 9.7 75 8 7% 332 34 30% 100 10 9% 2826 F 11 10.4 150 15 17% 333 42 38% 150 15 17% 239Mean 12.3 10.2 226 22 25% 386 40 41% 167 16 18% 252Model group7 M 8 6.5 275 42 43% 712 110 111% 350 54 55% 2288 M 9 8.7 200 23 28% 380 42 53% 120 14 17% 2749 M 14 10.6 300 28 29% 343 33 33% 200 19 19% 25910 M 10 10.8 250 23 31% 316 33 40% 150 14 19% 22811 M 9 9.5 250 26 35% 466 49 65% 200 21 28% 290Mean 10.0 9.2 255 29 33% 443 53 60% 204 24 27% 256Model v.s. non-model group (ManneWhitney

U-test, 2-tailed exact significance)0.52 0.25 0.25 0.79 0.93 0.33 0.36 0.43 0.25 0.99

D.P.F. van Nunen et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2014) 1e7 5

the comparison group (range: 181e310 min). Formal testing withthe ManneWhitney U-test revealed no statistically significant dif-ferences between the model and comparison groups in perioper-ative blood loss, volume of erythrocyte transfusion and length ofthe surgical procedure (Table 2).

4. Discussion

Given the complex nature of craniofacial anatomy three-dimensional representations of the skull have since long beenused by reconstructive surgeons for patient education, preoperativeplanning, intraoperative reference as well as for instruction toresidents and colleagues (D’Urso et al., 1998; Sailer et al., 1998).With the introduction of virtual three-dimensional reconstructionsof CT-imagery in the 1980s physical models were soon manufac-tured using Computer Numerical Control (CNC) milling techniques(Brix et al., 1985). The resulting models had certain limitations, asthin bony structures and internal cavities were difficult to recreatewith milling machines (Kragskov et al., 1996). Moreover, the foammaterial was brittle and soft and could not be sterilized (Klein et al.,1992). Brix and Lambrecht (1987) pioneered the use of stereo-lithography in the surgical planning for craniofacial surgery, whilein Mankovich et al. (1990) were the first to apply the technology tothe treatment plan for a craniofacial deformity. Although theearliest models suffered from artificial contours and inaccuracies(Sinn et al., 2006), ongoing technological development has dimin-ished the cephalometric deviations of stereolithographic skullmodels to fractions of millimetres (Schicho et al., 2006; Silva et al.,2008; Taft et al., 2011).

The objective of the present studywas to assess the use of three-dimensional stereolithographic skull models in the surgical treat-ment of trigonocephaly with respect to the effects on the volumesof intraoperative blood loss, transfusion requirements and length ofthe surgical procedure. The analysis showed that the use of ster-eolithographic models did not lead to a significant reduction in themean volume of allogeneic erythrocyte transfusions in the peri-operative period. Neither did the use of stereolithographic modelsresult in significant declines in the mean volume of perioperativeblood loss and mean length of the surgical procedure. In the liter-ature two studies conducted an analysis analogous to our own.

Imai et al. (1999) examined whether simulated surgery onthree-dimensional milled models of the skull would lead to areduction in the volume of intraoperative erythrocyte transfusion

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and procedural length in the surgery for craniosynostosis ascompared to preoperative planning with virtual three-dimensionalskull reconstructions. During surgical planning milled models wereordered for nine patients undergoing fronto-orbital advancementwhile virtual reconstructions were made for six similar patients.After simulation of the surgical procedure on the milled and virtualreconstructions Imai et al. observed a significant reduction(P ¼ 0.039) in the mean volume of intraoperative erythrocytetransfusion from 65.8 ml/kg to 26.3 ml/kg for the subgroup of eightpatients that received fronto-orbital advancement withoutremodelling. However, in the subgroup of seven patients treated byfronto-orbital advancement with remodelling no significantreduction (P ¼ 0.213) was found. In addition, their results showedthat the use of milled models had no impact on the mean length ofsurgery. Unfortunately, no information was provided on the in-dications for the surgical procedures performed.

In a second Japanese study, Uemura et al. (2001) described theirexperiences with the employment of solid skull models in cranio-synostosis surgery. In the preoperative phase the intended surgicaltechniques were simulated on three-dimensional stereolitho-graphic skull models of four patients awaiting fronto-orbitaladvancement with remodelling for Crouzon syndrome, oxy-cephaly, plagiocephaly or Apert syndrome. The resulting volumesof blood loss, erythrocyte transfusions and length of the subsequentsurgical procedure were compared to those of four historical pa-tients that were treated by fronto-orbital advancement withremodelling because of Crouzon syndrome, plagiocephaly orbrachycephaly. Uemura et al. did not find a significant differencebetween the two groups of patients in terms ofmean intraoperativeblood loss, volume of erythrocyte transfusion and length of surgery.

Based on the results of the three studies discussed, there is littleevidence that the usage of three-dimensional solid models in thesurgical planning for fronto-orbital advancement (with remodel-ling) leads to a notable decrease in the volumes of erythrocytetransfusion and blood loss or to a reduction in procedural length.Nonetheless, our experience is that stereolithographic skull modelsdo indeed possess beneficial qualities in the clinical pathway fortrigonocephaly. First, themodels greatly facilitated the education ofpatients’ parents about both the condition and the plannedcorrective surgical procedure when compared with virtual re-constructions alone. Parents appreciated the ability to take themodels in their hands and to examine these from all angles. Second,after sterilization the models were used as intraoperative reference

hic skull models in the surgical planning of fronto-supraorbital barllo-Facial Surgery (2014), http://dx.doi.org/10.1016/j.jcms.2014.01.017

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and frequently consulted during surgery. Although the modelsfailed to affect the duration of the procedures, members of thesurgical team commented positively on their immediate availabil-ity and tactile properties. Outside of the clinic, the models wereemployed in the teaching and training of surgical residents andstudents of the university medical school. The models enhancedthe understanding of the relevant anatomy and the side-by-sidecomparison of the pre- and postoperative situations readilyconveyed the rationale of fronto-supraorbital advancement andremodelling in the treatment of trigonocephaly. Moreover, theteachers unanimously felt that the introduction of the modelsenlivened the classes.

The disadvantages of procuring the stereolithographic models inthe preoperative periodwere predominantly the cost of eachmodeland, to a lesser degree, the delivery time of around five work days.Since two skull models were ordered for each patient in the modelgroup, the mean cost of treatment increased by an amount of V1.800,. At a time when efforts are made nation-wide to reduce therise of healthcare expenditure this extra cost for no apparentclinical gain is difficult to justify from a cost-benefit perspective. Forfuture patients the existing stock of skull models could satisfy therequirements for parent education and informed consent. Likewise,the instruction of residents and students has no need for additionalmodels of the same clinical entity. Contrary to Imai et al. andUemura et al. the surgical simulation in our study was done on avirtual reconstruction of the skull and the planned postoperativeresult was then manufactured by stereolithography. Accordingly,the simulation could just as well be performed entirely on a soft-ware package for Computer-Aided Surgical Simulation (CASS)without need of a physical model. The experience with CASS in thefield of craniofacial surgery has been thus far been supportive(Girod et al., 2001; Gateno et al., 2007; Rodt et al., 2007; Herlinet al., 2013). Moreover, the intraoperative anatomical referenceprovided by the stereolithographic models could be replaced bymore accurate systems of surgical navigation (Metzger et al., 2007;Collyer, 2010; Yu et al., 2013), an example of which is already in useby the department of oral and maxillofacial surgery within ourinstitution. Consequently, following this argument the CraniofacialCenter of WCH decided against standard acquisition of stereo-lithographic models in the treatment protocol of trigonocephaly.However, we feel that physical three-dimensional models remainessential in the surgical planning for more complex forms of cra-niosynostosis, such as those found in Apert or Crouzon syndromes.

The main strength of this study is the first systematic evaluationof stereolithographic skull models in the surgical treatment fortrigonocephaly with regards to its effect on the volumes of bloodloss, transfusion requirements and length of the surgical procedure.In addition, given the unreliability of the reported volumes of bloodloss, the study employs a more realistic estimate of intraoperativeblood loss based on pre- and postoperative haemoglobin levels andthe volume of erythrocyte transfusions received. Despite thesestrengths, the study is subject to several limitations. First, thesubjects were not randomized between the model and non-modelgroups and a caseecontrol design was used instead. Second, thenumber of patients in both the model group and non-model groupwas limited preventing a more thorough statistical analysis.

5. Conclusion

The usage of stereolithographic skull models in the surgicalplanning for the treatment of trigonocephaly does not reduce themean volume of perioperative erythrocyte transfusions, the meanvolume of perioperative blood loss or the mean length of the sur-gical procedure. Physical skull models do nevertheless remainessential in the treatment protocol for more complex types of

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craniosynostoses. Moreover, they have an important secondary rolein facilitating the education of a patient’s parents and in elucidatingthe relevant anatomy and the mode of treatment to surgical resi-dents and medical students.

Conflict of interest statementNone.

FundingNone acquired.

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