case report, Dr. Alireza Ghassemi

1. Computer-assisted zygoma reconstruction with
vascularized iliac crest bone graft
Ali Modabber1
*
Marcus Gerressen1
Nassim Ayoub1
Dirk Elvers1
Jan-Philipp Stromps2
Dieter Riediger1
Frank Hölzle1
Alireza Ghassemi1
1
Department of Oral, Maxillofacial
and Plastic Facial Surgery, RWTH
Aachen University Hospital, Germany
2
Department of Plastic, Hand and
Burn Surgery, RWTH Aachen
University Hospital, Germany
*Correspondence to: A. Modabber,
Department of Oral, Maxillofacial and
Plastic Facial Surgery, RWTH Aachen
University Hospital, Pauwelsstrasse
30, 52074 Aachen, Germany. E-mail:
amodabber@ukaachen.de
Abstract
Background The reconstruction of zygoma is a challenge with regard to aes-
thetic and reconstructive demands.
Methods Pre-operative CT data were imported into specific surgical planning
software. The mirror-imaging technique was used. A surgical guide transferred
the virtual surgery plan to the operation site, whereby it fitted uniquely to the
iliac donor site. A postoperative CT scan was obtained for comparing the actual
postoperative graft position and shape with the pre-operative virtual simulation.
Results A mean difference of 0.71 mm (SD ± 1.42) for the shape analysis and
3.53 mm (SD ± 3.14) for the graft position was determined. The calculation of
the closest point distance showed a surface deviation of < 2 mm for the shape
analysis with 83.6% of values and for the graft position with 35.7% of values.
Conclusion Virtual surgical planning is a suitable method for zygoma recon-
struction with vascularized iliac crest bone graft, with good accuracy for restoring
the three-dimensional anatomy. Copyright © 2013 John Wiley & Sons, Ltd.
Keywords computer-assisted surgery; virtual planning; vascularized iliac crest
bone graft; surgical guide; zygomatic reconstruction
Introduction
Malar and zygomatic arch defects often occur after cancer surgery, resection of
benign maxillary tumours and trauma. The localization, extension and dimen-
sions of the defect provide important information for the surgical treatment.
Brown and Shaw (1) described a new classification for maxilla and mid-face
defects. However, this classification does not include the zygomatic arch, and
this region represents a complex anatomical structure. There are many
therapeutic options to restore complex craniofacial defects. Microvascularized
bone flaps present an excellent therapeutic alternative for zygoma reconstruc-
tion with autologous transplants. Microsurgically revascularized iliac crest
bone grafts have the benefit of a rich cancellous blood supply, a large amount
of bone and a compact cortex (2), providing an ideal site for the reconstruction
of malar and zygomatic arch defects. The aesthetic outcome and satisfying
facial appearance of the reconstruction depends on the position and shape of
the graft.
Three-dimensional (3D) modelling, assisted by computed tomography (CT),
can be an ideal method for obtaining precise information for reconstructive
surgery. The transformation of digital CT data to 3D software for the simula-
tion of the operative field and the donor region provides a detailed and precise
analysis. It serves as a diagnostic tool to plan the size, shape and exact
ORIGINAL ARTICLE
Accepted: 10 October 2013
Copyright © 2013 John Wiley & Sons, Ltd.
THE INTERNATIONAL JOURNAL OF MEDICAL ROBOTICS AND COMPUTER ASSISTED SURGERY
Int J Med Robotics Comput Assist Surg 2013; 9: 497–502.
Published online 6 November 2013 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/rcs.1557

2. placement of the bone graft (3), which may be of impor-
tant clinical benefit. Virtual pre-operative planning
provides accuracy in detail without loss of information,
and a number of alternative surgical approaches can be
visualized (4). Using surgical planning software to simu-
late various surgical scenarios can be convenient and
cost-effective (5).
For an accurate translation of the virtual pre-operative
planning to real-time surgery, operation templates
fabricated by a selective laser-sintering technique provide
a precise modelling of the detailed anatomical structures
of the defect. Various approaches demonstrate the benefit
of prefabricated 3D image templates, linking the virtual
operation plan to the actual surgical procedure (6–9).
Computer-assisted surgery can help facilitate the shap-
ing procedure of the bone graft and to increase precision
in order to achieve an optimal aesthetic outcome (10),
as well as a shortening of transplant ischaemia time (11).
The aim of this study was to determine the accuracy of
computer-assisted zygoma reconstruction with vascularized
iliac crest bone graft and, consequently, whether it should
be routinely used for all patients undergoing bony recon-
struction of malar and zygomatic arch defects.
Materials and methods
After institutional approval and written, informed consent,
the translation from a virtual plan to the operating site with
a surgical guide was performed in a patient with a gunshot
defect of the left malar and zygomatic arch.
Pre-operative CT scans of the facial skeleton and iliac
crest were performed with a 128 row multislice CT scan-
ner (Somatom Definition Flash, Siemens, Erlangen, Ger-
many). Reconstructions were carried out in a bone and
soft tissue window, kernel 30/60 for head and neck and
70 for the pelvis. Acquisition of scans for head and neck
is done in 0.5 mm slice thickness, for the pelvis in 1 mm
slice thickness.
The CT data of the facial skeleton in digital imaging and
communications in medicine (DICOM) file format were
imported into ProPlan CMF Planning Software (Materialise
N.V., Leuven, Belgium). The process of segmentation
followed, in which artifacts were removed and all bony
structures of interest were isolated. A high-quality 3D visu-
alization of the mid-face was calculated. The mirror image
of the healthy side served as reference for the virtual recon-
struction of the affected malar and zygomatic arch.
Figure 1. Comparison of the actual postoperative graft position (violet) with the virtually planned situation (green): (A) bottom
view; (B) frontal view
498 A. Modabber et al.
Copyright © 2013 John Wiley & Sons, Ltd. Int J Med Robotics Comput Assist Surg 2013; 9: 497–502.
DOI: 10.1002/rcs

3. Additionally, angiographic CT scans of the iliac donor site,
which also allowed investigation of the arteries, were read
in with the software. Depending on the vascularization,
the position of the graft selected afterwards was
determined at the right iliac crest. After virtual reconstruc-
tion of the defect area, as mentioned above, the best-fitting
part of the iliac crest was selected. The positions of the
vessels nourishing the iliac graft were also taken into
account. The donor site was virtually osteotomized and
replaced into the zygoma defect. After fine adjustment,
the data were imported into 3-matic software (Materialise
N.V.) as an STL file. Thus, based on the final plan, a surgical
guide fitting uniquely to the iliac crest, and indicating the
desired osteotomy lines, graft size and angulation, was
designed. With the aid of the rapid prototyping selective
laser-sintering method, the guide was produced out of
polyamide powder and solidified using a carboxide laser.
The surgical guide linked the computer-assisted surgical
plan to real-time surgery.
A postoperative CT scan was obtained after 6 months to
compare 3D computer models of the final reconstruction
with the pre-operative virtual plan. Using 3-matic software,
the pre- and postoperative objects were first aligned using
point registration. Thereafter, automatic global surface reg-
istration was performed; this registration is based on an
iterative closest point (ICP) algorithm. The remaining skull,
after resection, was used to register the postoperative to the
pre-operative situation, as it is important to use those ob-
jects that remain unchanged through the surgery.
The actual postoperative graft position was compared
with the virtual simulation (Figure 1). This was done
based on a part comparison algorithm that measures the
distance of every triangle corner of the postoperative sur-
face against the planned surface. This resulted in a set of
measurements that were analysed in a histogram. The
colour map overlay histograms represented a close prox-
imity of objects coloured green and red to show the in-
crease of distance differences from the pre-operative plan.
To compare the actual postoperative graft shape with
the virtual simulation, again the global surface registra-
tion was performed, using only the actual postoperative
and simulated graft (Figure 2A, B). The same process
was used in 3-matic as for the graft position comparison.
Results
The presented surgical method of zygoma reconstruction
allowed the implementation of predetermination of the iliac
Figure 2. Comparison of the actual postoperative graft shape (violet) with the pre-operative planned shape of the graft (green): (A)
lateral view; (B) medial view
Computer-assisted zygoma reconstruction 499
Copyright © 2013 John Wiley & Sons, Ltd. Int J Med Robotics Comput Assist Surg 2013; 9: 497–502.
DOI: 10.1002/rcs

4. graft with regard to its shape, size and the site of osteotomy
during surgery. Its temporary fixation on the donor site sim-
plified the surgical procedure (Figure 3). Guided surgical
sawing of the iliac crest reduced the amount of removed
bone to the determined level (Figure 4) and it fitted into
the zygoma defect without major adjustments (Figure 5).
No complications were encountered during the surgery or
healing phase. The microsurgically revascularized iliac crest
bone graft showed excellent perfusion. Comparison of
the pre- and postoperative 3D computer models using a part
comparison algorithm showed a mean difference of 0.71 mm
(SD± 1.42) for the shape analysis and 3.53 mm (SD± 3.14)
for the graft position. The part comparison-based closest
point distance of the absolute values indicated that 83.6%
of surface deviation was< 2 mm for the shape analysis.
The surface deviation showed a 35.7% smaller difference
than 2 mm for the position analysis. The absolute count of
measured points in each calculation using the part compari-
son algorithm was 7113 points (ED, element distribution).
The colour map overlay histograms (Figure 6A, B) showed
the results of the surface deviation analysis for shape and
position of the iliac crest bone graft.
Discussion
There are many therapeutic options for restoring the facial
skeleton. The most commonly used alloplastic implants for
zygomatic reconstruction can cause postoperative compli-
cations, such as foreign body reaction, swelling, infection
and replacement (12). Using autologous bone flaps such
Figure 3. The surgical guide is temporarily fixed on the exter-
nal side of the right iliac, using osteosynthesis screws. Arrow
points to the deep circumflex iliac artery at the medial side of
the iliac crest
Figure 4. The iliac crest bone graft, exactly sawed and osteotomized
with the help of the surgical guide
Figure 5. Positioning and fixation of the iliac crest bone graft for
reconstruction of the left malar and zygomatic arch. Arrow
points to the anastomosis of the deep circumflex iliac vessel to
the left temporal vessels
Figure 6. The surface deviation analysis for shape (A) and posi-
tion (B) of the iliac crest bone graft. The calculation showed a
surface deviation of < 2 mm (red line) for the shape analysis with
83.6% of values and for the graft position with 35.7% of values.
ED, element distribution
500 A. Modabber et al.
Copyright © 2013 John Wiley & Sons, Ltd. Int J Med Robotics Comput Assist Surg 2013; 9: 497–502.
DOI: 10.1002/rcs

5. as fibula, iliac crest or scapula is an excellent way of
reconstructing complex craniofacial defects.
Brown and Shaw (1) described the use of microvascu-
lar iliac crest bone grafts for the reconstruction of defects
after maxillectomy, with and without involving the orbit
(class I–IV). However, this classification has a weakness
with respect to zygomatic defects which involve the
zygomatic arch. Microvascular iliac crest bone graft also
provides a perfect anatomy and bony structure to restore
the curvature of the zygomatic arch (Figure 7A, B). The
vascularized iliac crest graft has a short pedicle, which
means that careful planning is required (13).
The goal of zygoma reconstruction is to achieve the
maximum aesthetic outcome. Therefore, pre-operative
virtual planning can help to evaluate the defect size and
the relation to neighbouring structures in order to choose
the best possible reconstruction plan. The analysis of the
entire facial skeleton in 3D provides more accuracy, makes
an overall evaluation possible and supplies valuable
information which greatly facilitates further treatment.
The virtual surgery plan requires a precise 3D model,
conforming to the standards of the defect, as the basis for
the design of the transplant in shape, position and angula-
tion. Different surgical tools are required from the software
to perfect the virtual plan. The mirroring tool allows the use
of the healthy side as a template for computational super-
imposition on the affected side, for the restoration of facial
symmetry (14). However, the use of the mirroring tool can
influence the accuracy of the pre-operative virtual plan
because of the natural asymmetry of humans skulls (15).
The present study, which uses the computer-assisted
method ProPlan CMF (Materialise N.V.), previously
described for mandibular and maxillary reconstruction
with microvascular bone flaps (10,11,16), is the first for ma-
lar and zygomatic arch reconstruction. It delivers a surgical
guide for intra-operative use, based on an accurate virtual
operation plan, which is made with the aid of simulation
before surgery. The goal was to evaluate the accuracy of this
method for malar and zygomatic arch reconstruction with a
microvascular iliac crest bone graft.
The registration of the pre- and postoperative data for a
comparison of the virtual and actual postoperative situations
can give an idea of whether the surgery has been performed
in accordance with the pre-operative virtual plan. In order to
compare the 3D computer models from the final reconstruc-
tion with the pre-operative virtual plan, a postoperative CT
scan was obtained after 6 months. The remodelling and
resorption of the graft take place mainly in the first 6 months
after transplantation (17) However, the measurements rep-
resent the result after the remodelling phase has been com-
pleted, which is very important for the long-term aesthetic
outcome. A mean difference of 0.71 mm (SD ± 1.42) with
83.6% surface deviation < 2 mm for the shape analysis
was calculated. It seems that the actual shape comes very
close to the virtual plan. The surgical guide ensures accurate
sawing of the iliac graft during the surgical procedure, with
a determined transplant shape, size and number and site of
osteotomies. The immediate insertion of the graft into the
zygoma defect followed the explantation, as no time for
shaping was necessary.
The measurements for the graft position showed a mean
difference of 3.53 mm (SD ± 3.14) with a 35.7% smaller
difference than 2 mm in the surface deviation calculation.
It appears that the exact placement of the bone graft into
the zygoma defect is very difficult without predefined bony
margins. Roser et al. showed a mean maximum distance of
2.00 mm (SD ± 1.12) of postoperative mandibular resection
margins to that of the virtual plan (18). This reflects the fact
that the anatomy and 3D structure of the zygoma seems to
be more complex. However, the achieved aesthetic outcome
was very satisfactory (Figure 8A, B). It appears that the
natural asymmetry of faces in humans obscures some inac-
curacy in surgical reconstructions to a certain degree (15).
The use of computer-assisted techniques in combination
with free flaps provides good functional and aesthetic results
with predictable outcome (19). A surgical guide transfers
the computer-based surgical plan to real-time surgery, which
is the required procedure to achieve the best possible result.
The clinical benefits of computer-assisted surgery are likely
to outweigh the expenditure for technology (20). Surgical
guides shorten transplantation time, increase precision and
control and minimize the shaping process of the transplant
(11). The increased accuracy ensures outcomes of constant
high quality as regards both shape and aesthetics. Growing
Figure 7. Cone beam computed tomography (CBCT) of the pre-operative zygomatic bone defect (A) and postoperative result (B) of
the anatomical reconstruction, with contouring accuracy of the zygomatic arch
Computer-assisted zygoma reconstruction 501
Copyright © 2013 John Wiley & Sons, Ltd. Int J Med Robotics Comput Assist Surg 2013; 9: 497–502.
DOI: 10.1002/rcs

6. complexity in extensive bony defects may raise this method’s
indication, as the surgery might be well simplified for such
defect location, which is difficult to achieve through manual
placement of the graft, even for experienced surgeons (18).
The presented method shows that using custom-made sur-
gery guides using vascularized iliac crest bone graft can help
to restore complex areas, such as the malar and zygomatic
arch, with good accuracy. We are aware that a randomized
prospective trial with larger sample sizes will be required to
evaluate further benefits of computer-assisted zygoma recon-
structions with vascularized iliac crest bone grafts.
Acknowledgements
The authors thank Annelies Genbrugge and Joris Bellinckx
(Materialise N.V., Leuven, Belgium) for their valuable support.
Conflict of Interest
The authors have stated explicitly that there are no conflicts
of interest in connection with this article.
References
1. Brown JS, Shaw RJ. Reconstruction of the maxilla and midface: in-
troducing a new classification. Lancet Oncol 2010; 11: 1001–1008.
2. Riediger D. Restoration of masticatory function by microsurgically
revascularized iliac crest bone grafts using enosseous implants.
Plast Reconstr Surg 1988; 81: 861–876.
3. Marentette LJ, Maisel RH. Three-dimensional CT reconstruction in
midfacial surgery. Otolaryngol Head Neck Surg 1988; 98: 48–52.
4. Schramm A, Gellrich NC, Schmelzeisen R. Navigational Surgery
of the Facial Skeleton. Springer-Verlag: Berlin, Heidelberg, New
York, 1997; 1–51.
5. Hallermann W, Olsen S, Bardyn T, et al. A new method for
computer-aided planning for extensive mandibular reconstruc-
tion. Plast Reconstr Surg 2006; 117(7): 2431–2437.
6. Yang X, Hu J, Zhu S, et al. Computer-assisted surgical planning
and simulation for condylar reconstruction in patients with
osteochondroma. Br J Oral Maxillifac Surg 2011; 49: 203–208.
7. Rose EH, Norris MS, Rosen JM. Application of high-tech three-
dimensional imaging and computer-generated models in complex
facial reconstructions with vascularized bone grafts. Plast Reconstr
Surg 1993; 91: 252–264.
8. Liu XJ, Gui L, Mao C, et al. Applying computer techniques in
maxillofacial reconstruction using a fibula flap: a messenger
and an evaluation method. J Craniofac Surg 2009; 20: 372–377.
9. Feng F, Wang H, Guan X, et al. Mirror imaging and preshaped ti-
tanium plates in the treatment of unilateral malar and zygomatic
arch fractures. Oral Surg Oral Med Oral Pathol Oral Radiol Endod
2011; 112: 188–194.
10. Modabber A, Gerressen M, Stiller MB, et al. Computer-assisted
mandibular reconstruction with vascularised iliac crest bone
graft. Aesthet Plast Surg 2012; 36: 653–659.
11. Modabber A, Legros C, Rana M, et al. Evaluation of computer-
assisted jaw reconstruction with free vascularized fibular flap
compared to conventional surgery: a clinical pilot study. Int J
Med Robot 2012; 8: 215–220.
12. Binder WJ, Azizzadeh B. Malar and submalar augmentation.
Facial Plast Surg Clin North Am 2008; 16: 11–32.
13. Brown JS, Jones DC, Summerwill A, et al. Vascularized iliac crest
with internal oblique muscle for immediate reconstruction after
maxillectomy. Br J Oral Maxillofac Surg 2002; 40: 183–190.
14. Scolozzi P. Maxillofacial reconstruction using polyetheretherketone
patient-specific implants by ’mirroring’ computational planning.
Aesthet Plast Surg 2012; 36: 660–665.
15. Metzger MC, Hohlweg-Majert B, Schön R, et al. Verification of
clinical precision after computer-aided reconstruction in
craniomaxillofacial surgery. Oral Surg Oral Med Oral Pathol Oral
Radiol Endod 2007; 104: e1–e10.
16. Leiggener C, Messo E, Thor A, et al. A selective laser sintering
guide for transferring a virtual plan to real time surgery in com-
posite mandibular reconstruction with free fibula osseous flaps.
Int J Oral Maxillofac Surg 2009; 38: 187–192.
17. Verhoeven JW, Ruijter J, Cune MS, et al. Onlay grafts in combina-
tion with endosseous implants in severe mandibular atrophy:
one year results of a prospective, quantitative radiological study.
Clin Oral Implants Res 2000; 11: 583–594.
18. Roser SM, Ramachandra S, Blair H, et al. Accuracy of virtual
surgical planning in free fibula mandibular reconstruction: com-
parison of planned and final results. J Oral Maxillofac Surg 2010;
68: 2824–2832.
19. Kokemueller H, Tavassol F, Ruecker M, et al. Complex midfacial
reconstruction: a combined technique of computer-assisted
surgery and microvascular tissue transfer. J Oral Maxillofac Surg
2008; 66: 2398–2406.
20. Ewers R, Schicho K, Undt G, et al. Basic research and 12 years of
clinical experience in computer-assisted navigation technology:
a review. Int J Oral Maxillofac Surg 2005; 34: 1–8.
Figure 8. (A) Pre-operative left facial gunshot defect with affected malar and zygoma arch. (B) Postoperative facial symmetry after
computer-assisted zygoma reconstruction with vascularized iliac crest bone graft
502 A. Modabber et al.
Copyright © 2013 John Wiley & Sons, Ltd. Int J Med Robotics Comput Assist Surg 2013; 9: 497–502.
DOI: 10.1002/rcs