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

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Stereolithographic skull models in the surgical planning of frontosupraorbital 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, * a Department of Plastic and Reconstructive Surgery (Head: M. Kon), University of Utrecht Medical Center, Heidelberglaan 100, PO Box 85500, 3508 GA Utrecht, The Netherlands b Department of Neurosurgery (Head: L.P.E. Regli), University of Utrecht Medical Center, Heidelberglaan 100, PO Box 85500, 3508 GA Utrecht, The Netherlands c Department 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

a b s t r a c t

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

Background: Fronto-supraorbital bar advancement in the treatment for trigonocephaly is associated with extensive intraoperative blood loss and compensatory erythrocyte transfusions. Since both are related to the length of surgery, efforts have been focused on optimizing preoperative preparations. The utilization of three-dimensional skull models in surgical planning allows for familiarization with the patient’s anatomy, the optimization of osteotomies, the preparation of bone grafts and the selection of fixation plates. Methods: Stereolithographic skull models were used in the surgical planning for five patients with nonsyndromic trigonocephaly treated in Wilhelmina Children’s Hospital in 2012. A comparison group was composed of six patients with non-syndromic trigonocephaly treated by the same surgical team. Once all patients had received surgery, a retrospective chart review was performed to identify the volumes of perioperative blood loss and erythrocyte transfusions and the length of the procedure. Furthermore, the educational value of the models was assessed in a round table discussion with the surgical team and residents. 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 perioperative blood loss of 53 ml/kg (60% of EBV) in the model group against 40 ml/kg (41% of EBV) in the comparison group (P ¼ 0.792). The mean length of surgery in the model groups was 256 min versus 252 min in the comparison group (P ¼ 0.995). Evaluation of educational purposes demonstrated that the models had a role in the instruction of residents and communication to parents, but did not improve the insight of experienced surgeons. Conclusion: The usage of stereolithographic skull models in the treatment of non-syndromic trigonocephaly does not reduce the mean volume of perioperative erythrocyte transfusions, the mean volume of perioperative blood loss nor the mean length of the surgical procedure. Nonetheless, the models do facilitate the education of the patient’s parents as well as support the training of residents. Ó 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.

Keywords: [MeSH] Craniosynostoses Trigonocephaly Metopic synostosis Imaging Three-dimensional

1. Introduction Trigonocephaly is a craniosynostosis characterized by a wedgeshaped forehead with a midline ridge due to restricted transverse

* Corresponding authors. Department of Oral-Maxillofacial Surgery, University of Utrecht Medical Center, Heidelberglaan 100, PO Box 85500, 3508 GA Utrecht, The Netherlands. Tel.: þ31 88 77 57751; fax: þ31 88 75 55504. E-mail addresses: [email protected] (D.P.F. van Nunen), marvickmuradin@ gmail.com (M.S.M. Muradin).

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

1010-5182/$ e see front matter Ó 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jcms.2014.01.017

Please cite this article in press as: van Nunen DPF, et al., Stereolithographic skull models in the surgical planning of fronto-supraorbital bar advancement for non-syndromic trigonocephaly, Journal of Cranio-Maxillo-Facial Surgery (2014), http://dx.doi.org/10.1016/j.jcms.2014.01.017

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

a syndrome in 35% of patients (Lajeunie et al., 1998). Delays in neuropsychological development have been reported for 15e62% of patients (Oi and Matsumoto, 1987; Sidoti et al., 1996; Aryan et al., 2005; Engel et al., 2012). The aetiology of metopic synostosis remains unknown (Engel et al., 2012; van der Meulen, 2012), but it is often ascribed to either an intrinsic malformation of the frontal bones (Lajeunie et al., 1998; Rasmussen et al., 2007; Wilkie et al. 2007; Senarath-Yapa et al. 2012) fetal head constraints in the pelvic area during pregnancy (Graham and Smith, 1980; Smartt et al., 2005) or to a malformation of the frontal lobes leading to a reduction of stimuli for cranial growth (Moss, 1959; Senarath-Yapa et al. 2012). Surgical intervention is warranted in order to increase the volume of the underdeveloped anterior cranial fossa as well as to improve aesthetics (Panchal and Uttchin, 2003; Forrest and Hopper, 2013). Since the publication of the classic papers by Hoffman and Mohr (1976) and Marchac (1978) surgical techniques involving advancement of the fronto-supraorbital bar with remodelling of the frontal bone have become the standard in the treatment of trigonocephaly. Disadvantages of these procedures are the extensive amount of intraoperative blood loss and associated transfusion rates (Stricker et al., 2010), both of which are correlated to the duration of surgery (White et al., 2009; van Uitert et al., 2011). Efforts to reduce the length of corrective surgery have been partially focused on enhancing preoperative preparations. One approach has been the use of three-dimensional physical models in surgical planning, which allows for familiarization with the patient’s anatomy, the optimization of osteotomies, the preparation of bone grafts and the selection of fixation plates (D’Urso et al., 1998; Sailer et al., 1998; Sannomiya et al., 2006; Sinn et al., 2006). The objective of the present study is to evaluate the use of threedimensional stereolithographic models in the surgical treatment for trigonocephaly with regards to its effect on the volumes of blood loss, transfusion requirements and length of the surgical procedure. 2. Material and methods In order to evaluate the added value of three-dimensional solid models in the treatment protocol for non-syndromic trigonocephaly, stereolithographic models were ordered for a series of five consecutive patients referred to the Craniofacial Centre of the Wilhelmina Children’s Hospital in 2012. The comparison group consisted of all prior patients with non-syndromic trigonocephaly treated by the same surgical team, which took its current form in mid-2009. Once all patients in the model group had received corrective surgery, a retrospective chart review was conducted for both groups in which the following characteristics were recorded for each patient: demographics, past medical history, prescription drugs, duration of the surgical procedure, reported blood loss during surgery and the volumes of packed erythrocytes transfused in the peri- and postoperative periods. The retrospective chart review was approved beforehand by the local Medical Ethics Committee. Given the inherent difficulty of accurately measuring perioperative blood loss in craniosynostosis surgery (Stricker et al., 2010; Goobie et al. 2011), a second estimate of the perioperative blood loss was calculated following the methodology of Kearney et al. (1989) (Table 1). The duration of the surgical procedure was defined as the timespan between the start of surgical preparations after induction of general anaesthesia and the end of surgical wound closure. The primary endpoint of this study was the volume of allogeneic erythrocyte transfusion in the peri- and postoperative periods. Secondary endpoints were the estimated volume of blood loss and the duration of the surgical procedure. Statistical analysis was

Table 1 Estimated 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) Estimated Red Cell Mass (ERCM, ml) ¼ EBV  Haematocrit (l/l) Haematocrit of packed erythrocytes at WCH ¼ 0.60 l/l ERCMlost ¼ ERCMpreoperative þ ERCMtransfused  ERCMpostoperative Estimated Blood Loss (EBL, ml) ¼ ERCMlost/Haematocritpreoperative

2 3 4

performed with IBM SPSS Statistics 20.0 (IBM Inc, New York, NY, USA) using the ManneWhitney U-test. A P-value of less than 0.05 was considered statistically significant. 2.1. Stereolithographic models e Production and employment After their first visit to the outpatient clinic of the Craniofacial Centre of WCH all patients in this study underwent a helical volume CT-scan of the cranium following the standard diagnostic protocol. The CT-scans were performed at a gantry tilt of 0 , a tube current of 100 mA at 90 kV and with a slice thickness of 1 mm. The scan data of the model group were transferred to Materialise N.V. (Leuven, Belgium) and uploaded into the proprietary surgical planning software package Synthes ProPlan CMF (Synthes Holding AG, Solothurn, Switzerland). During an interactive online planning session the operation was simulated on a virtual three-dimensional reconstruction of the skull following the directions of the surgical team (Fig. 1). The desired postoperative result was converted to the STL-file format accepted by the stereolithography threedimensional printers. The production of the models started with a bath filled with a liquid UV-sensitive resin in which an immersed platform was raised to a level just below the surface. Subsequently, the stereolithography printer guided a heliumecadmium laser beam over the surface polymerizing the resin and constructing the initial layer of the model. The platform with the initial layer was then slightly lowered allowing the laser beam to create the second layer. This process was then repeated until all layers of the model were formed. Next, the model was removed from the bath and excess resin and support struts were cleared by hand. In the final step the model was placed in a UV-oven which increased the strength of the model by completing the process of photopolymerization and cross-linking of the resin. For each patient in the model group two distinct skull models were ordered: one of the preoperative situation (Fig. 2) and one of the desired postoperative situation (Fig. 3). Delivery of the models to the WCH required five work days after the order was placed with Materialize N.V. The costs per individual skull model amounted to V 900 e and were covered by the patients’ health insurance plans. During the preoperative period the three-dimensional models were used 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 sterilization the models were brought into theatre on the day of surgery to allow for quick intraoperative evaluation of the patients’ cranial anatomy and surgical plan. 3. Results The five patients in the model group were all males, on average ten months of age at the date of surgery with a body weight of 9.2 kg (Table 2). The comparison group consisted of six patients, of which three were females, who received surgery at a mean age of 12.3 months weighing a mean 10.2 kg. No patient in either group

Please cite this article in press as: van Nunen DPF, et al., Stereolithographic skull models in the surgical planning of fronto-supraorbital bar advancement for non-syndromic trigonocephaly, Journal of Cranio-Maxillo-Facial Surgery (2014), http://dx.doi.org/10.1016/j.jcms.2014.01.017

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

3

Fig. 1. Surgical planning.

had a history of cardiopulmonary or haematologic disease. Prescription drugs influencing the coagulation process were not taken by any patient in the preoperative period. All trigonocephaly patients were treated by fronto-supraorbital advancement and remodelling in an open procedure. Haemostasis was performed

using bipolar electrocoagulation, bone wax and, in all patients, by the administration of tranexamic acid during surgery. The mean reported perioperative blood loss in the model group was 29 ml/kg (or 33% of Estimated Blood Volume [EBV]) with a range of 23e42 ml/kg (28e43% of EBV), see Table 2. Patients in the

Please cite this article in press as: van Nunen DPF, et al., Stereolithographic skull models in the surgical planning of fronto-supraorbital bar advancement for non-syndromic trigonocephaly, Journal of Cranio-Maxillo-Facial Surgery (2014), http://dx.doi.org/10.1016/j.jcms.2014.01.017

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Fig. 2. Stereolithographic skull model e preoperative situation.

comparison group reportedly lost a mean 22 ml/kg of blood (25% of EBV) varying between 8 and 41 ml/kg (7e46% of EBV). Following the method by Kearney et al. the perioperative blood loss amounted to a mean 53 ml/kg (60% of EBV) with a range of 33e100 ml/kg (33e 111% of EBV) in the model group and up to a mean of 40 ml/kg (or 41% 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 administered between 14 and 54 ml/kg of allogeneic erythrocyte

transfusions (17e55% of EBV) with a mean of 24 ml/kg (or 27% of EBV). In the comparison group patients received a mean 16 ml/kg (or 18% of EBV) of allogeneic erythrocytes with a range of 10e30 ml/ kg (9e34% of EBV). In the postoperative period no additional erythrocyte transfusions were given to any patient. Autologous erythrocyte transfusions were not used. No transfusion reactions were observed. In the model group the surgical procedure required a mean time of 256 min (range: 228e290 min), compared to a mean 252 min in

Fig. 3. Stereolithographic skull model e desired preoperative situation.

Please cite this article in press as: van Nunen DPF, et al., Stereolithographic skull models in the surgical planning of fronto-supraorbital bar advancement for non-syndromic trigonocephaly, Journal of Cranio-Maxillo-Facial Surgery (2014), http://dx.doi.org/10.1016/j.jcms.2014.01.017

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Table 2 Results. Subject

Gender (M/F)

Age (months)

Weight (kg)

Non-model group 1 M 14 10.9 2 M 12 10.6 3 F 11 9.9 4 M 11 9.8 5 F 15 9.7 6 F 11 10.4 Mean 12.3 10.2 Model group 7 M 8 6.5 8 M 9 8.7 9 M 14 10.6 10 M 10 10.8 11 M 9 9.5 Mean 10.0 9.2 Model v.s. non-model group (ManneWhitney U-test, 2-tailed exact significance)

Estimated blood loss

Erythrocyte transfusion

Reported

Kearney-method

To tal (ml)

ml/kg

% EBV

Total (ml)

200 300 404 225 75 150 226

18 28 41 23 8 15 22

19% 33% 46% 26% 7% 17% 25%

609 405 480 160 332 333 386

275 200 300 250 250 255 0.52

42 23 28 23 26 29 0.25

43% 28% 29% 31% 35% 33% 0.25

712 380 343 316 466 443 0.79

the comparison group (range: 181e310 min). Formal testing with the ManneWhitney U-test revealed no statistically significant differences between the model and comparison groups in perioperative blood loss, volume of erythrocyte transfusion and length of the surgical procedure (Table 2). 4. Discussion Given the complex nature of craniofacial anatomy threedimensional representations of the skull have since long been used by reconstructive surgeons for patient education, preoperative planning, intraoperative reference as well as for instruction to residents and colleagues (D’Urso et al., 1998; Sailer et al., 1998). With the introduction of virtual three-dimensional reconstructions of CT-imagery in the 1980s physical models were soon manufactured using Computer Numerical Control (CNC) milling techniques (Brix et al., 1985). The resulting models had certain limitations, as thin bony structures and internal cavities were difficult to recreate with milling machines (Kragskov et al., 1996). Moreover, the foam material was brittle and soft and could not be sterilized (Klein et al., 1992). Brix and Lambrecht (1987) pioneered the use of stereolithography in the surgical planning for craniofacial surgery, while in Mankovich et al. (1990) were the first to apply the technology to the treatment plan for a craniofacial deformity. Although the earliest models suffered from artificial contours and inaccuracies (Sinn et al., 2006), ongoing technological development has diminished the cephalometric deviations of stereolithographic skull models to fractions of millimetres (Schicho et al., 2006; Silva et al., 2008; Taft et al., 2011). The objective of the present study was to assess the use of threedimensional stereolithographic skull models in the surgical treatment of trigonocephaly with respect to the effects on the volumes of intraoperative blood loss, transfusion requirements and length of the surgical procedure. The analysis showed that the use of stereolithographic models did not lead to a significant reduction in the mean volume of allogeneic erythrocyte transfusions in the perioperative period. Neither did the use of stereolithographic models result in significant declines in the mean volume of perioperative blood loss and mean length of the surgical procedure. In the literature two studies conducted an analysis analogous to our own. Imai et al. (1999) examined whether simulated surgery on three-dimensional milled models of the skull would lead to a reduction in the volume of intraoperative erythrocyte transfusion

ml/kg

% EBV

58 41 51 17 34 42 40

58% 45% 55% 18% 30% 38% 41%

110 42 33 33 49 53 0.93

111% 53% 33% 40% 65% 60% 0.33

Duration of surgery (min)

Total (ml)

ml/kg

% EBV

250 100 300 100 100 150 167

23 10 30 10 10 15 16

24% 11% 34% 11% 9% 17% 18%

258 310 181 239 282 239 252

350 120 200 150 200 204 0.36

54 14 19 14 21 24 0.43

55% 17% 19% 19% 28% 27% 0.25

228 274 259 228 290 256 0.99

and procedural length in the surgery for craniosynostosis as compared to preoperative planning with virtual three-dimensional skull reconstructions. During surgical planning milled models were ordered for nine patients undergoing fronto-orbital advancement while virtual reconstructions were made for six similar patients. After simulation of the surgical procedure on the milled and virtual reconstructions Imai et al. observed a significant reduction (P ¼ 0.039) in the mean volume of intraoperative erythrocyte transfusion from 65.8 ml/kg to 26.3 ml/kg for the subgroup of eight patients that received fronto-orbital advancement without remodelling. However, in the subgroup of seven patients treated by fronto-orbital advancement with remodelling no significant reduction (P ¼ 0.213) was found. In addition, their results showed that the use of milled models had no impact on the mean length of surgery. Unfortunately, no information was provided on the indications for the surgical procedures performed. In a second Japanese study, Uemura et al. (2001) described their experiences with the employment of solid skull models in craniosynostosis surgery. In the preoperative phase the intended surgical techniques were simulated on three-dimensional stereolithographic skull models of four patients awaiting fronto-orbital advancement with remodelling for Crouzon syndrome, oxycephaly, plagiocephaly or Apert syndrome. The resulting volumes of blood loss, erythrocyte transfusions and length of the subsequent surgical procedure were compared to those of four historical patients that were treated by fronto-orbital advancement with remodelling because of Crouzon syndrome, plagiocephaly or brachycephaly. Uemura et al. did not find a significant difference between the two groups of patients in terms of mean intraoperative blood loss, volume of erythrocyte transfusion and length of surgery. Based on the results of the three studies discussed, there is little evidence that the usage of three-dimensional solid models in the surgical planning for fronto-orbital advancement (with remodelling) leads to a notable decrease in the volumes of erythrocyte transfusion and blood loss or to a reduction in procedural length. Nonetheless, our experience is that stereolithographic skull models do indeed possess beneficial qualities in the clinical pathway for trigonocephaly. First, the models greatly facilitated the education of patients’ parents about both the condition and the planned corrective surgical procedure when compared with virtual reconstructions alone. Parents appreciated the ability to take the models in their hands and to examine these from all angles. Second, after sterilization the models were used as intraoperative reference

Please cite this article in press as: van Nunen DPF, et al., Stereolithographic skull models in the surgical planning of fronto-supraorbital bar advancement for non-syndromic trigonocephaly, Journal of Cranio-Maxillo-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 models failed to affect the duration of the procedures, members of the surgical team commented positively on their immediate availability and tactile properties. Outside of the clinic, the models were employed in the teaching and training of surgical residents and students of the university medical school. The models enhanced the understanding of the relevant anatomy and the side-by-side comparison of the pre- and postoperative situations readily conveyed the rationale of fronto-supraorbital advancement and remodelling in the treatment of trigonocephaly. Moreover, the teachers unanimously felt that the introduction of the models enlivened the classes. The disadvantages of procuring the stereolithographic models in the preoperative period were predominantly the cost of each model and, to a lesser degree, the delivery time of around five work days. Since two skull models were ordered for each patient in the model group, the mean cost of treatment increased by an amount of V 1.800,. At a time when efforts are made nation-wide to reduce the rise of healthcare expenditure this extra cost for no apparent clinical gain is difficult to justify from a cost-benefit perspective. For future patients the existing stock of skull models could satisfy the requirements for parent education and informed consent. Likewise, the instruction of residents and students has no need for additional models of the same clinical entity. Contrary to Imai et al. and Uemura et al. the surgical simulation in our study was done on a virtual reconstruction of the skull and the planned postoperative result was then manufactured by stereolithography. Accordingly, the simulation could just as well be performed entirely on a software package for Computer-Aided Surgical Simulation (CASS) without need of a physical model. The experience with CASS in the field of craniofacial surgery has been thus far been supportive (Girod et al., 2001; Gateno et al., 2007; Rodt et al., 2007; Herlin et al., 2013). Moreover, the intraoperative anatomical reference provided by the stereolithographic models could be replaced by more accurate systems of surgical navigation (Metzger et al., 2007; Collyer, 2010; Yu et al., 2013), an example of which is already in use by the department of oral and maxillofacial surgery within our institution. Consequently, following this argument the Craniofacial Center of WCH decided against standard acquisition of stereolithographic models in the treatment protocol of trigonocephaly. However, we feel that physical three-dimensional models remain essential in the surgical planning for more complex forms of craniosynostosis, such as those found in Apert or Crouzon syndromes. The main strength of this study is the first systematic evaluation of stereolithographic skull models in the surgical treatment for trigonocephaly with regards to its effect on the volumes of blood loss, transfusion requirements and length of the surgical procedure. In addition, given the unreliability of the reported volumes of blood loss, the study employs a more realistic estimate of intraoperative blood loss based on pre- and postoperative haemoglobin levels and the volume of erythrocyte transfusions received. Despite these strengths, the study is subject to several limitations. First, the subjects were not randomized between the model and non-model groups and a caseecontrol design was used instead. Second, the number of patients in both the model group and non-model group was limited preventing a more thorough statistical analysis. 5. Conclusion The usage of stereolithographic skull models in the surgical planning for the treatment of trigonocephaly does not reduce the mean volume of perioperative erythrocyte transfusions, the mean volume of perioperative blood loss or the mean length of the surgical procedure. Physical skull models do nevertheless remain essential in the treatment protocol for more complex types of

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Please cite this article in press as: van Nunen DPF, et al., Stereolithographic skull models in the surgical planning of fronto-supraorbital bar advancement for non-syndromic trigonocephaly, Journal of Cranio-Maxillo-Facial Surgery (2014), http://dx.doi.org/10.1016/j.jcms.2014.01.017

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Please cite this article in press as: van Nunen DPF, et al., Stereolithographic skull models in the surgical planning of fronto-supraorbital bar advancement for non-syndromic trigonocephaly, Journal of Cranio-Maxillo-Facial Surgery (2014), http://dx.doi.org/10.1016/j.jcms.2014.01.017

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

Fronto-supraorbital bar advancement in the treatment for trigonocephaly is associated with extensive intraoperative blood loss and compensatory erythr...
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