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24 Technical Performance of the Personalized Approach in Combined Guided Orthognathic/Bone…
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331
CT Scan Data
Thresholding and 3D
Modeling
Use Patient’s
Contralateral Side to
Mirror Contours
Is the Correction
Acceptable?
YES
Complete Surgery /
Revision
Patient Follow-up as
Needed
Surgery / Osteotomy
NO
Reposition
Assess Correction of
Volume Deficiency
Design Implant for
Correction
Manufacture Implant
(mill / 3D print)
Compare Plan to
Actual Outcome
Fig. 24.5 Workow of scanned data into the patient-specic model process
The prediction from the autogenous skeletal
reconstruction approach is presented in Fig.24.6
on the top row. Various designs of the osteotomy
and reposition could not achieve the tolerance
limit for asymmetry by the patient and the surgeon. A custom alloplastic implant was designed
that would achieve the desired symmetry and is
presented in Fig.24.6 on the bottom row. For the
alloplastic implant approach, Boolean operation
(on polygons) [40] was used to calculate the differences between the actual skeletal surface and
the reference surface, and then the initial design
of the implant was extracted accordingly. The initial draft following exactly the contralateral (mirrored) side included features that would be
unfavorable to the manufacture process or to the
patient, such as thin edges on the angle or the
nasal area. The implant was thus designed with
smooth surfaces to avoid any sharp edges.
Moreover, based on the surgeon’s feedback and
clinical expertise, the design was improved by
adding extensions to the lateral orbital rim and
zygomatic process to avoid any potential instability in the long term.
An acrylic model (optional) can be delivered
to the surgeon as shown in Fig.24.7. The HTRPMI implant with the nal design was made
using porous PMMA material (Biomet
Microxation, Jacksonville, FL, USA). The
implants were delivered to the operation room
directly.
After the skeletal surface was exposed, the
implant tted well to the surface topography and
was then xed with titanium screws, as shown in
Fig. 24.7, top and bottom rows. Intraoperative
exposure of the osseous defects was facilitated by
on-site inspection of the acrylic skull model. No
unexpected deformities or untoward injuries
were encountered during the operation. The
HTR-PMI implant t extremely well, and conse-
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S.-O. Streubel et al.
Fig. 24.6 (Top) Prediction from the autogenous skeletal
reconstruction approach and with aligned osteotomies.
(Bottom) Custom alloplastic implant that was designed to
fully achieve the facial symmetry and allow for soft tissue
augmentation of the nal correction
24 Technical Performance of the Personalized Approach in Combined Guided Orthognathic/Bone…
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Fig. 24.7 Example of acrylic 3D model that can be made to help explain the surgery to the patient. Preoperative model
(left), planned model (right)
333
Fig. 24.8 Comparison between planned (left) and postoperative outcome (right). Note: The PEEK implants are not
displayed on the postoperative image because they cannot be segmented from CT images
quently, no adjustments were needed. The patient
was followed for several months, and the facial
symmetry was achieved. There were no complications. Figure 24.8 shows the postoperative
outcome.
Future Directions
With the rapid development of biotechnology,
significant transformation and innovation in
craniomaxillofacial surgery can be expected in
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S.-O. Streubel et al.
the next decade. The confluence of image
acquisition technologies into extended reality,
the integration of artificial intelligence, and
the advancement of robotic technology will
likely make the reconstruction of maxillofacial deformities more patient specific, minimally invasive, precise, and safer. Alloplastic
implants will be replaced with biocompatible
osteoconductive resorbable implants with
intrinsic controlled release of bone growth
factors, hormones, antibiotics, and stem cells.
Patient-specific custom implants made with
autogenous, adipose-derived, stem cells
(ASCs) in custom bioreactors have already
proven efficacy and superiority to traditional
implants in large animal studies. Bhumiratana
etal. (2016) [42] demonstrated that anatomically correct bone grafts from ASCs were
grown and implanted in Yucatan mini-pigs to
reconstruct the ramus- condyle unit. In certain
circumstances, fetal surgery will allow for
correction of craniomaxillofacial deformities
in utero during fetal development. The
advancement of remote surgery will support
broader access of reconstructive procedures to
rural communities. Digital health technologies
will have the potential for real-time postoperative monitoring and intervention in the home
setting and integration with the patient’s electronic medical record. Patients should experience less invasive, safer, and accurate surgery
with faster recovery times, fewer outcome
inconsistencies, and more local access.
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Planning Principles inDistraction
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Osteogenesis Including
Simultaneous CAD/CAM-Based
Facial Reconstructions
ValentinKerkfeld andUlrichMeyer
25
Introduction
A myriad of strategies and procedures have been
used in an attempt to generate rst an optimal
result concerning the complex facial functions
(biting, chewing, speaking, mimicking), and second a harmonious and symmetrical appearance
for patients with complex facial malformations.
Both hard and soft tissue reconstruction is
required in the treatment process.
Bone Tissue Reconstruction
ThroughDO
The hard tissue aspect is accomplished by bone
movement surgery, which has been established in
the form of orthognathic surgery for many
decades. Although conventional OGS is based on
a long tradition with many successful cases in
craniofacial reconstruction, modern craniofacial
surgery is in transition. In this context, a deeper
understanding of the biological systems is
improving the therapeutic principles. DO is an
extremely prominent example in this regard.
V. Kerkfeld (*)
Clinic for Maxillofacial and Plastic Facial Surgery,
Westdeutsche Kieferklinik; University of Düsseldorf,
Düsseldorf, Germany
U. Meyer
Center for Jaw-, Face- and Skull Surgery,
Münster, Germany
e-mail: praxis@mkg-muenster.de
© Springer Nature Switzerland AG 2023
U. Meyer (ed.), Fundamentals of Craniofacial Malformations,
https://doi.org/10.1007/978-3-031-28069-6_25
Continuous improvements have been achieved
through advancements in DO techniques and
other modern procedures. DO techniques are
used in craniofacial malformation treatment for
deformity correction through lengthening, widening, and bone transport. Surgical techniques
span the range from alveolar ridge augmentation,
over midface and upper face advancement, to
skull construction procedures.
Distraction osteogenesis is indicated mainly
due to two aspects: (1) when the extent of bone
movement crosses distinct distances and (2)
when soft tissue deciencies or scars impede
bone movements. Both factors are often relevant
in craniofacial malformations.
1. In orthognathic surgery, bone displacements
up to a maximum of 7mm are tolerable, as
displacements greater than 10mm are considered at high risk of relapse [1, 2]. However,
DO offers a popular method for such displacements, which allows displacements of more
than 10 mm to be performed in a relatively
stable manner [3, 4].
2. In patients with craniofacial deformities (e.g.,
syndromal craniosynostosis, branchial arch
diseases, or orofacial clefts), who present with
more extended soft tissue deciencies or scars
(based on prior surgery), DO is excellently
suited because it has high postoperative stability [5–8] and involves displacement in the
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V. Kerkfeld and U. Meyer
biological sense as part of the accompanying
histogenesis [7].
Distraction Biology
First, osteotomy is performed along the planned
line so that at least two bone fragments are created. Then the distractor is mounted. After a short
latency period during which the osteotomy site
matures, the distraction phase begins. In the subsequent distraction phase (1–2weeks), the constant traction provides a modication of the
regeneration process. Tissue develops in parallel
with the distraction vector along with angiogenesis and spindle-shaped broblast-like cells.
Distraction follows a regular pattern, resulting in
the separation of individual bone fragments. This
induces new bone formation at the osteotomy
site. Various distraction protocols are in use.
Ilizarov [9, 10] established the tension-stress law
and dened a distraction rate of 1mm per day as
optimal. Distraction creates parallel bundles of
collagen bers, which also serve nerves’ blood
vessels as an ideal guide structure. Higher distraction rates can quickly lead to hematomas or
even necrosis at the osteotomy site, which delays
healing immensely [11, 12]. Still, further
increases in distraction rates lead to even more
complications such as nonunion, brous union,
or bone weakening. Furthermore, collateral damage to the surrounding soft tissues follows [13].
Decreasing rate may lead to premature consolidation, especially in complex 3D sites, as it is
present in DO through a bisagittal split osteotomy (BSSO).
A multistep, strain-related segment movement
was shown to lead to an optimized callus healing
[14–17]. Once the planned length is achieved,
distraction is stopped and the callus is given the
opportunity to mature. This phase (consolidation
phase) lasts from weeks to months. At this time
point, three surgical strategies can be used: (1)
the timely removal of the distractor and plating of
segments, (2) the timely removal of the distractor
and ne adjustment by elastics (with the possibility of callus shaping), or (3) the removal of the
distractor at the end of the consolidation phase.
Distractor Types
Distractors can be applied both intraorally and
extraorally. Intraoral distractors can be further
divided into tooth-supported, bone-supported,
and hybrid models. Extraoral distractors, however, are always bone-supported. Compared to
intraoral distractors, extraoral distractors have
the advantage that the vectors can be selected
more exibly. This can also be controlled during
distraction and changed if necessary. This reduces
failures and increases predictability [18–20].
CAD/CAM Strategies ofCombined DO
andSoft Tissue Augmentation
Today, CAD/CAM technology offers extensive
support in the planning and treatment of complex
jaw malpositions. With its help, the patient’s initial situation is recorded by means of threedimensional X-ray imaging (CBCT, CT) and
intraoral scanning. The data generated in this
way can be matched and combined to form an
exact three-dimensional image of the patient’s
situation. Virtual surgery is recently performed
on this basis in complicated cases. Subsequently,
patient-specic interocclusal splints (also in use
as gliding splint with nal position stops) as well
as cutting and drilling devices for distractor
placement can be fabricated. Distraction osteogenesis itself does not mandate complex virtual
preoperative planning to simulate threedimensional (3D) movements in all situations,
whereas in case of osteotomies that involve 3D
movements of maxillomandibular complex or if
DO is applicated simultaneously with soft tissue
augmentation, virtual planning is superior to conventional surgery. The planning procedure with
prefabricated cutting and drilling devices ensures
an exact transfer of the planned situation to the
intraoperative situs and enables therefore also the
application of distraction devices, having control
over the distraction vector.
Distraction Vector
The determination of the distraction vector
depends on the denition of the nal treatment
aim. The distraction vector is crucial for planning
25 Planning Principles in Distraction Osteogenesis Including Simultaneous CAD/CAM-Based Facial…
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339
the distraction, since the vector and the position
of the distraction device are decisive for the subsequent displacement of the bone fragments [21]
(Fig.25.1). The extent of bone movements is dictated by the normal anatomy. Figure 25.1 displays a patient with an extreme maxillary
retrognathia, based on a bilateral cleft, lip, and
palate. To restore a class I occlusion and at the
same time improve the oral mouth volume and
gain a harmonious facial appearance, the maxillary advancement must lead to a normal SNA
value. The mandible pushback distance (to reach
a normal SNB value) is much lower. In this way,
the hard tissue conversion even about high distances already achieves the highest degree of
accuracy and plannability. When inserting intraoral distractors, nasal intubation should be performed so that the endotracheal tube does not
present an obstacle during placement. For DO, a
prolonged treatment period (3–6months) should
be planned so that the rigid distractor can provide
stabilization of the bone. The consolidation phase
(8–12weeks) ensures stable bonding of the bone
fragments. An acceleration of the treatment time
can be achieved by removing the distractor earlier and applying osteosynthesis plates, as this
maneuver improves the patient’s quality of life
during this stage of treatment and reduces the
possibility of a bony relapse.
Soft Tissue Augmentation
Despite an almost ideal bone conguration after
the bone movement, even if it is extensive, however, an ideal harmonic symmetry of the face is
not automatically achieved. For this, other components must be considered. First and foremost,
the soft tissue must be considered, consisting of
fatty tissue and muscles, which have an enormous effect on the facial appearance. In addition,
the reconstruction of bones by DO cannot compensate for all bone anatomies, so that, for example, aplastic zygomatic bones must be augmented.
Numerous autologous and allogenic techniques
are used for augmentation. In particular, autogenous bone grafts and free ap plasty are used to
ll large tissue defects. However, these procedures have signicant disadvantages. First, they
are associated with donor-site morbidity because
the healthy donor site is surgically intervened.
Furthermore, implantation of autologous materials often leads to resorption and nonhealing [22].
Thus, allogeneic techniques have been developed
such as silastic porous polyethylene. However,
these materials can lead to immune reactions, so
that the augmentation is rejected as a result of
severe inammation [23]. For this reason, a
robust material was required that, on the one
hand, had the best material properties (strength,
Fig. 25.1 (a)
Preoperative lateral
ceph, (b) during the
distraction phase and (c)
after the removal of the
distractor (plating of the
maxilla) and pushback
surgery of the maxilla.
Note the position of both
distractors leading to a
vector parallel to the
occlusal plane
a
b
c
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V. Kerkfeld and U. Meyer
stiffness, durability) and, on the other hand, was
biocompatible so as not to provoke an immune
reaction. A new advancement in craniofacial surgery came from the technical industry implementing a widely established material,
polyetheretherketone (PEEK), in this eld.
Subsequent studies also proved its biocompatibility [24–26]. PEEK implants have been in use
for several years in the treatment of cervical disk
disease, replacing autogenous bone grafts in
anterocervical fusion [27, 28]. As time went on,
reconstructive practitioners also recognized the
potential of the new material [29, 30]. Scolozzi
and Martinez [31] are considered one of the rst
users of PEEK in craniofacial reconstruction,
who used PEEK augmentation to reconstruct a
complex orbito-fronto-temporal defect situation
in 2007.
Data Generation
For virtual planning and execution of DO and
augmentation surgery, the necessary patient data
must be generated. In principle, a single threedimensional scan of the patient is sufcient to
generate all the necessary data. However, three
different procedures are necessary, as each of
them can depict certain parameters very well, but
others not at all or only poorly. Therefore, a 3D
bone scan, a dental arch scan, and a surface scan
are performed. The data collected in this way are
then matched in a coherent volume.
Dental Arch andOcclusion
Although three-dimensional radiographs using
CBCT or CT also provide an image of the teeth,
this is very inaccurate due to massive artifact formation and therefore unusable. Artifact formation is further exacerbated by the xed orthodontic
appliances often found in patients with craniofacial malformations [34]. For this reason, a threedimensional dental arch scan is performed to
replace the artifact-affected portion of the radiographically determined volume. The dental arch
scan can be performed either directly on the
patient by means of a laser intraoral scan or on a
previously fabricated plaster model of the patient
[35, 36].
Facial Texture
While hard tissue structures can be detected very
well with X-ray imaging, soft tissue structures
and especially the skin surface and color can only
be imaged with difculty and poor contrast. In
addition, this would not produce a photorealistic
image that also depicts the skin texture. For this
reason, modern color scans are used to record the
facial texture in three dimensions in a short time
and with high precision [37]. In a next step, the
data can be transferred to the existing volume
model.
Procedure
Bony Skull
Most of the information for creating the volume
that virtually represents the patient’s baseline
situation is generated by cone beam CT (CBCT)
or conventional CT (CT). Both techniques provide excellent data on high-contrast structures
such as the bony skeleton [32]. Here, CBCT often
gets by with a much lower radiation dose and
provides better quality images than CT [33]. The
dataset is then exported in Digital Imaging and
Communications in Medicine (DICOM) format
and is available for further processing.
Preoperative planning proceeds in a step-bystep procedure. First, the orthognathic procedure or DO procedure is planned. The
augmentation of soft tissue by CAD/CAM fabricated bone onlay implants is then planned on
this basis of the planned nal bone position. The
treatment goal is generally to achieve the jaw
position by superimposing a normal skull mirroring the healthy side. In asymmetric patients,
the two datasets (superimposition of normal
scan or mirroring of a “healthy” side towards
the diseased site) can be averaged. Once planning is complete, the practitioner receives an
25 Planning Principles in Distraction Osteogenesis Including Simultaneous CAD/CAM-Based Facial…
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overview and the appropriate patient-specic
cutting and drilling guides for distractor insertion and the PEEK implants.
Considerations
Distraction osteogenesis planning is based primarily on data from the bony skull (Fig.25.2). In
this context, the therapy of complex craniofacial
malformations is subject to some difculties, so
that some aspects must be considered. Frequently,
a major bone displacement is necessary, so that
DO is the best option. Special anatomical decits
(like aplastic ramus in branchial arch diseases)
must be detected and treated by special osteotomies. Most craniofacially deformed skulls have
a
signicant deviation in all three spatial directions
(sagittal, transverse, and frontal), leading to the
correspondingly frequent presence of facial
asymmetries. Due to this, three-dimensional
planning tools are obligatory. Conventional
methods, such as lateral cephalographies, cannot
be used in these complex conditions.
With the aim of achieving the greatest possible facial harmony and symmetry, the addition of
auxiliary tools is necessary. On the one hand, a
standard skull adapted to the age and size of the
patient is used as a guide. In the case of asymmetrical facial proportions, the healthy side of
the face can also be mirrored. The nal decision
as to which modication is performed and to
what extent is highly complex. The following
questions help to answer it:
b
c
Fig. 25.2 Preoperative situation of a patient with apert syndrome. (a) Facial appearance, (b) occlusal view, (c) lateral
cephalogram
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