Accepted Manuscript

Comparing Two Fronto-orbital Advancement Strategies to Treat Trigonocephaly inMetopic Synostosis

Philipp Metzler, MD,DMD Harib H. Ezaldein, BS John A. Persing, MD Derek M.Steinbacher, MD, DMD

PII: S1010-5182(14)00129-2

DOI: 10.1016/j.jcms.2014.04.006

Reference: YJCMS 1782

To appear in: Journal of Cranio-Maxillo-Facial Surgery

Received Date: 2 March 2014

Revised Date: 11 April 2014

Accepted Date: 15 April 2014

Please cite this article as: Metzler P, Ezaldein HH, Persing JA, Steinbacher DM, Comparing Two Fronto-orbital Advancement Strategies to Treat Trigonocephaly in Metopic Synostosis, Journal of Cranio-Maxillofacial Surgery (2014), doi: 10.1016/j.jcms.2014.04.006.

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Comparing Two Fronto-orbital Advancement Strategies to Treat Trigonocephaly in

Metopic Synostosis

Philipp Metzler (MD,DMD), Harib H Ezaldein (BS); John A Persing (MD).; Derek M

Steinbacher (MD, DMD)

Plastic and Reconstructive Surgery

Yale University School of Medicine

330 Cedar St, BB 3rd Floor

New Haven, CT 06520

Corresponding author:

Derek M. Steinbacher MD, DMD

Plastic and Craniomaxillofacial Surgery, Yale University School of Medicine

330 Cedar St, BB 3rd Floor

New Haven, CT 06520

Tel.: +1 (203) 785 4559

Fax: +1 (203) 785 7514

E-mail address: derek.steinbacher@yale.edu

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Summary

Background: Trigonocephalic treatment entails frontoorbital reshaping of the forehead,

increasing bitemporal dimensions, and advancing lateral orbits. Various techniques can achieve

this, but no consensus exists regarding effects on long-term skull growth. Overcorrecting

forehead dimensions is one strategy though preserving a vascularized fronto-orbital bar can

influence future growth. We therefore seek to craniomorphologically compare fronto-orbital

advancement (FOA), using bandeau widening and advancement, to a pedicled “tilt” procedure to

assess whether adequate 3D remodeling is achieved.

Methods: Demographic and computed tomographic data was recorded. Pre-and post-

craniometric measurements were performed for the endocranial bifrontal angle, orbital plane

angle, anterior advancement and the interzygomaticofrontal suture distance.

Results: 40 CT scans were analyzed, with similar demographics. No perioperative complications

were encountered. The endocranial bifrontal angle increased in the FOA (p=0.00026) and tilt

groups (p=0.00297), along with the orbital plane angles (FOA, p=0.020498; tilt, p=0.07371), the

anterior advancement (FOA, p=0.00932; tilt, p=0.05823), and the interzygomaticofrontal suture

distance(FOA, p=0.001241; tilt, p=0.07811).

Conclusions: Both techniques improve frontoorbital dimensions for correction of metopic

synostosis. In severe trigonocephaly phenotypes, the FOA allows a greater magnitude of

expansion and overcorrection, but compromises preservation of a vascularized leash. The “tilt”

procedure possesses the benefit of near-anatomic bandeau remodeling, while potentially

improving long-term growth.

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Keywords

Tilt procedure, fronto-orbital advancement, trigonocephaly, metopic, suture, metopic synostosis,

cranial vault remodeling.

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Level of Evidence: LEVEL II (PRS, Comparison with gold-standard

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Introduction

Treatment goals for metopic synostosis include expansion and advancement of the supralateral

bandeau, widening of the temporal dimensions, and rounding the forehead. Several techniques

have been espoused to achieve these objectives, and have evolved over time (Tessier, 1967;

Tessier, 1971; Hoffman and Mohr, 1976; Marchac, 1978; Marchac and Renier, 1979;

Obwegeser, 2009). In addition to aesthetic correction, a marked increase of the endocranial

volume within the anterior cranial fossa occurs (Renier et al., 1982; van der Meulen, 2012). This

allows expansion of the brain into the area, with an increased blood supply and mitigation of

intracranial hypertension providing a corollary benefit to brain development and psychomotor

abilities (Renier et al., 1982; Sidoti et al., 1996; Schaller et al., 2012). However, traditional

expansion techniques have shown a tendency toward the original deformity with long-term

surveillance (Cohen et al., 1991; Fearon et al., 2009). This subsequent supralateral orbital rim

restriction is thought secondary to diminished intrinsic growth, inadequate surgical expansion,

and devascularization of segments at the time of advancement or some combination (McCarthy

et al., 1990; Cohen, 1996; Losken et al., 1996). Overcorrection has been advocated to account for

the anticipated relapse or growth restriction (Fearon, 2008; Fearon et al., 2009). Another

strategy suggested is to maintain a vascularized pedicle to the advanced bandeau while “tilting”

the segment forward (Hoffman and Mohr, 1976; Patel et al., 2012).

In our unit, both surgical techniques, the modified “fronto-orbital advancement” and the “tilt-

procedure” are routinely used for metopic synostosis correction (Selber et al., 2007; Patel et al.,

2012). The purpose of this study is to objectively analyze the frontoorbital morphology achieved

comparing these two distinct techniques.

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Materials and Methods

This is a retrospective analysis performed in concordance with the Yale University Institutional

Review Board (protocol: HIC# 1101007932). Consecutive infants with metopic synostosis who

underwent treatment by the senior authors (J.A.P. or D.M.S.) at Yale were included.

Demographic and surgical data were tabulated, computed tomographic scan information were

obtained for both patients groups (fronto-orbital advancement (FOA, figure 1) and tilt procedure

(TP, figure 2). Technical details of each procedure is described in Figures 1 and 2, based on

previous descriptions (Tessier, 1967; Hoffman and Mohr, 1976; Marchac, 1978; Patel et al.,

2012). CT scan images were digitized from pre- and postoperative timepoints for each group and

analyzed using a surgical planning program (SurgiCase; Materialise, Leuven, Belgium).

Anatomic landmarks, measurements, and angles are shown in Table 1 and Figure 3. Percentages

of intra- and intergroup analysis were calculated (Tessier, 1967; Hoffman and Mohr, 1976;

Marchac, 1978; Patel et al., 2012). Statistical analysis involved the paired two-sample t-test. A

significant difference was noted with p-values <0.05.

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Results

Demographic data

Exactly 40 CT scans were included for analysis, 10 pre- and postoperative scans for the fronto-

orbital advancement and 10 pre- and postoperative scans for the tilt procedure. The FOA group

had 8 males and 2 females, with mean pre-op and post-op ages of 8 and 9.6months respectively.

The tilt group had 7 males and 3 females, with mean pre-op and post-op ages of 5 and 7.9

months. The average follow up time for the FOA and tilt groups is 1.5 months and 2.85 months

correspondingly. Post-operatively, all patients showed uneventful healing.

Endocranial bifrontal angle (ECA)

The endocranial bifrontal angle averaged 127.0° pre-op and 151.2° post-op, with a mean percent

change of 19.0% for the FOA group (p=0.00026). It averaged 129.3° preoperatively and 143.9°

post-operatively with a mean percent change of 11.3% for the tilt group (p=0.00297)(see Table

2).

Orbital plane angle (OPA)

The orbital plane angle in the FOA group measured on average 121.7° preoperatively and 132.0°

postoperatively, with an average 19 % change (p=0.020498). For the tilt procedure group, the

preoperative angle averaged at 119.8° and 129.9° postoperatively with an average correction of

11.3% (p=0.07371)(see Table 3).

Anterior advancement (AA)

The anterior advancement distance for the FOA group averaged at 43.8 mm preoperatively and

53.4 mm postoperatively, with an average percent change of 18.5 % (p=0.00932). The mean

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preoperative AA in the tilt group is 39.1 mm and 41.4 mm, postoperatively, with an average

percent change of 7.4 % (p=0.05823) (see Table 4).

Interzygomaticofrontal suture distance (ZFD)

The interzygomaticofrontal suture distance (ZF-ZF) distance for the FOA group averaged at

69.55 mm preoperatively and 76.38 mm postoperatively, with an average percent change of

9.81% (p=0.001241). The mean preoperative inter-ZF distance in the tilt group is 70.78 mm and

75.14 mm, postoperatively, with an average percent change of 6.16% (p=0.07811). These values

are listed in Table 5

Statistical evaluation showed in all measurements (ECA, OPA, AA, ZFD) significant higher (p ≤

0.05) postoperative changes in the FOA than in the Tilt group.

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Discussion

A variety of surgical strategies have been proposed to correct the characteristic trigonocephalic

stigmata seen in metopic synostosis. Advancing the supralateral orbit, expanding the temporal

dimensions, and rounding the forehead are the critical features of most techniques. In 1967,

Tessier et al. introduced the fronto-orbital advancement as the key procedure to correct forehead

dysplasia (Tessier, 1967; Tessier, 1971). Evolution and modification of this original technique

has been reported with excellent results (Hoffman and Mohr, 1976; Persing et al., 1990; Jimenez

et al., 2002; Knoll et al., 2005; Fearon, 2008; Shah et al., 2012). Nevertheless, hollowing, and

contour irregularities, as a function of return to original deformity, occur requiring revisions

(Cohen et al., 1991; Fearon et al., 2009; Steinbacher et al., 2011). The principle strategy to

minimize secondary procedures is to overexpand and overcorrect the supralateral dimensions

(Fearon, 2008; Fearon et al., 2009). The concept of maximizing perfusion of osseous segments

while limiting soft tissue forces and tension is also important (McCarthy et al., 1990; Cohen,

1996; Losken et al., 1996).

An ideal technique achieves both near anatomical correction and overcorrected dimensions to

account for future growth impairment (Fearon, 2008; Metzler et al., 2013). Further, the

technique should encourage brain-expansion and - growth. Beyond creating an excess of space

for the brain to expand, vascular preservation of the fronto-orbital bar may exhibit a major

influence on promotion e.g. growth and development and the brain-endocranial interface (Cohen,

1996; Losken et al., 1996; Francis et al., 2011).

The classic one-piece fronto-orbital advancement has long been the most common technique

used to correct metopic craniosynostosis and is still considered the gold standard. Evolution of

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this technique has involved a two-piece split, with intervening midline bone graft, and bone

shims placed from the orbital roof to the anterior cranial fossa (Selber et al., 2007; Francis et al.,

2011).

A number of craniometric analyses have been performed to shed insight on both the abnormal

findings characterizing metopic synostosis and the surgical morphological goals that should be

achieved with correction (Posnick et al., 1994; Havlik et al., 1999; Pearson et al., 2008; Beckett

et al., 2012; Kellogg et al., 2012). Three-dimensional planning and analysis has been proposed as

an effective means to achieve an ideal result, based on objective angles and parameters (Diluna

and Steinbacher, 2012; Shah et al., 2012). Similarly, an “average” frontoorbital bandeau guide

has been developed, based on a series on unaffected infants, and may be used to gauge treatment

(Burge et al., 2011). There is no consensus as to the ideal parameters of expansion and

positioning of the frontoorbital bandeau. Certainly with the advent of limited suturectomy

techniques and springs, there is no emphasis on temporal expansion and advancement, relying

solely on future brain growth. Most would agree that severe trigonocephaly, as classified by

Beckett et al., require a more complete, 3-dimentional remodeling technique involving fronto-

orbital bandeau repositioning (Francis et al., 2011; Beckett et al., 2012).

Accepting the tenet that in moderate-severe trigonocephaly, the angle of the frontoorbital bar

needs to be opened and the temporal aspects widened, we sought to investigate morphologic

differences between two techniques developed conserving these goals. To the authors’

knowledge, no study exists comparing various surgical techniques for trigonocephaly correction

in current literature. Therefore, the aim of this study was to compare the data of metopic

synostotic patients following the modified “fronto-orbital advancement” and the” tilt procedure”.

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Statistical analysis of both techniques showed significant differences between the pre- and

postoperative measurements focusing the fronto-orbital rim correction. Both techniques enable

the surgeon to positively influence the characteristic trigonocephalic stigma in all patients.

Within the FOA group, a large magnitude of correction is possible, consistent with the strategy

of overcorrection to account for future diminished growth. However, this is at the expense of

stripping all vascularized attachments to the bone. Inherently, because the tilt procedure

preserves the integrity of the fronto-nasal suture, the amount of sagittal correction is limited.

However, the amount of advancement required at the nasofrontal region is typically minimal.

Additionally, the tilt maneuver obviates an osseous step off above the nose, which may limit the

need for postoperative esthetic correction in this area. Another advantage of the ‘tilt procedure’

is the possibility for synchronous correction of zygomatic hypoplasia (Persing et al., 1990).

Technically, the tilt procedure, maintains the medial and lateral attachments of the frontonasal

and zygomaticofrontal sutures, and blood supply from the supraorbital and supratrochlear

arteries, and anterior branch of the superficial temporal artery. The superior and inferior latero-

orbital blood supply is maintained with periosteal preservation and connections of the deep

supraorbital and temporal with the zygomaticofacial and temporal arteries (Rene, 2006). The

preserved vascularization of this fronto-orbital segment may play a pivotal role in frontal sinus

development and function. McCarthy and colleagues noted a significant failure of the frontal

sinus development after FOA and complete periosteal stripping (McCarthy et al., 1990).

Importantly, the “pedicled” fronto-orbital segment may have a beneficial impact on long-term

growth results (Cohen, 1996; Losken et al., 1996; Patel et al., 2012).

The tilt procedure carries benefit when applied to younger infant, as this group has malleable

osseous segments, allowing greenstick. However, earlier surgical intervention is typically

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associated with a worsened degree of growth restriction. The preserved vascular supply in this

technique may offset this concern, not to mention the likely benefit of earlier surgery on

neuropsychiatric outcomes (Kapp-Simon, 1994). The degree of surgical correction achievable

using the tilt would certainly be well applied to the mild and moderate metopic synostosis. In

severe trigonocephalic phenotypes, the larger magnitude of movement possible with the FOA,

may allow for distinct 3D correction and overcorrection. Long-term analysis is necessary to fully

vet the concepts of over-expansion, growth promotion, and secondary deformities comparing the

two techniques.

Future work will focus on meticulous documentation of surgical age, phenotypic classification,

technique and magnitidue of correction, followed by close, long-term anthropometric analysis

shed further insight into the disease process and treatment strategies in metopic synostosis

(Metzler et al., 2013).

Conclusions

Two techniques for correction of trigonocephaly are compared. Both the tilt and FOA effectively

achieve surgical goals of frontoorbital expansion and advancement. The FOA allows for

overcorrection, with larger magnitude of advancement and expansion. Conversely the tilt

preserves osseous blood supply, which may portend improved growth outcomes. Future work is

geared toward longitudinal follow-up of these patients in relation to morphology and growth

outcomes

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Conflict of Interest Statement:

None of the authors has any financial or commercial interest in any aspect of this article.

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Tables

Table 1. Craniometric Parameters

Abbreviation Parameter Description

ECA Endocranial bifronal angle Angle of the frontal bone in a single axial plane at the level of the

superior-most aspect of the crista galli with the vertex (CG)

located on the endocranial side of the frontal bone at the metopic

suture and terminal points at the lateral borders of the respective

orbital apertures (OA right, OA left)

OPA Orbital plane angle Angle of both planes of the orbital aperture (supraorbital notch

(SON), zygomaticofrontal suture (ZF), zygomaticomaxillary

suture (ZM)

AA Anterior advancement Distance between the Clinoid (C) and the Glabella (G)

ZFD Interzygomaticofrontal suture

distance

Distance between zygomaticofrontal sutures (ZF)

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Table 2. Endocranial Bifrontal Angle (ECA) Before and After Surgical Correction of Metopic

Synostosis

FOA TP

Mean value (pre-op) 127.0° 129.3°

Mean value (post-op) 151.2° 143.9°

Mean change (pre/post-op) 24.18° 14.6°

Percentage 19.0% (max. 48.3 %) 11.3% (max. 18.2 %)

p-value 0.00026 0.00297

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Table 3. Orbital Plane Angle (OPA) Before and After Surgical Correction of Metopic Synostosis

FOA TP

Mean value (pre-op) 121.7° 119.8°

Mean value (post-op) 132.1° 129.9°

Mean change (pre/post-op) 10.4° 10.1°

Percentage 19.0 % (max. 26.5%) 11.3 % (max. 23.5%)

p-value 0.00026 0.00297

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Table 4. Anterior Advancement (AA) After Surgical Correction of Metopic Synostosis

FOA TP

Mean value (pre-op) 43.8 mm 39.1 mm

Mean value (post-op) 53.4 mm 41.4 mm

Mean change (pre/post-op) 8.3 mm 2.3 mm

Percentage 18.5 % (max 25%) 7.4 % (max 12.3%)

p-value 0.00932 0.05823

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Table 5. Interzygomaticofrontal Distance (ZFD) Before and After Surgical Correction of

Metopic Synostosis

FOA TP

Mean value (pre-op) 69.6° 70.8°

Mean value (post-op) 76.4° 75.1°

Mean change (pre/post-op) 6.8° 4.3°

Percentage 9.8 % (max. 20.5%) 6.2 % (max. 12.0 %)

p-value 0.001241 0.07811

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Captions to Illustrations

Figure 1

Pre-operative 3-D computed tomography scan of an eight months old patient with metopic

synostosis.

a) Coronal view, showing the craniocephalic landmarks used for antropometric

measurements

b) Axial view, showing the pre-operative measurements (endocranial bifrontal angle (ECA);

orbital planes angle (OPA))

Figure 2

Fronto-orbital Advancement (FOA)

A classical osteotomy was performed for fronto-orbital bar mobilization. For hypotelorism

correction, a two- piece opening and expansion of the supraorbital bar using an interpositional

bone graft was done.

a) Coronal view, showing the osteotomy lines and anterior advancement (medial and lateral

of the fronto-orbital segment) after remodeling.

b) Axial view, showing the complete mobilization (osteotomy line and advancement within

the frontal skull base) of the fronto-orbital segment.

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Figure 3

Tilt-Procedure (TP)

The osteotomy line is similar to that of the lateral canthal advancement, starting lateral of the

cribriform plate and runs along the orbital roof laterally including the greater wing of the

sphenoid and the lateral orbital wall, but excludes the fronto-zygomatic process. Furthermore, as

a key maneuver, the superolateral aspect of the supraorbital rim is greensticked anteriorly

maintaining the attachments within the frontonasal and frontozygomatic suture, allowing this

segment to pivot without compromising medial and lateral attachments. The fronto-orbital rim is

pivoted forward at the superior border without detaching the zygoma and skull base.

a) Coronal view, showing the osteotomy lines and lateral advancement of the orbital rim

after the tilt procedure. The naso-frontal segment is not been osteotomized and remains in

its continuity.

b) Axial view, showing the osteotomy line and lateral mobilization of the orbital rim. The

fronto-orbital segment remains pedicled within the frontal skull base, as shown. Mild

hypotelorism correction can be performed by a vertical osteotomy within the midsagittal

plane of the segment.

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Figures

Figure 1

Figure 2

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Figure 3