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C. Runte et al.

Fig. 19.3 Equipment for stereoscopic presentation. (a) Anaglyph glasses red/cyan, (b) circular polarizer glasses, (c) Lorgnette prism glasses, (d) over/under-prismatic viewer KMQ, (e) 3D World slide viewer and RBT frame,

viewing aids are shown in Fig.19.3. Anaglyph red/cyan glasses are cheap and effective. Conventional white screens and color monitors can be used with anaglyph glasses. However, this technique will interfere with color perception and has drawbacks in images with dominating red color, e.g., images showing surgical interventions.

(f) VR glasses for smartphones (a–e: Perspektrum 3D-shop, Nürnberg, Germany; e (frame): RBT Raumbildtechnik, Aichwald, Germany; f: Tepoinn, Shenzhen Jiateng Electronics, Shenzhen, China)

Images on cards, transparent lm, or displays can be viewed by special devices. Probably, the most popular slide viewer was the View-Master (Sawyer’s, Portland, USA). Today, smartphones can be used in viewers for stereoscopic virtual reality presentation.

The dominating technology used in cinemas is linear or circular polarization.

19 Stereoscopic Imaging ofCraniofacial Malformations

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255

Fig. 19.4 Stereo projection unit for a small auditorium. Left: Silver screen (Monika Awater 3D, Berlin, Germany), self- built rack with two superimposed NEC NP41 DLP

Polarizers do not interfere with color perception, but two projectors or a special projector with changing polarization and a silver screen are necessary and glasses are more expensive (Fig.19.4).

Publication of stereoscopic images in conven-

tional print media is possible by anaglyph tech-

beamers (NEC corp., Minato, Japan), and circular polarization lters; the computer with two graphics cards is located below

nique. Traditionally, in order to prevent color perception disturbances, prism glasses and viewers have been widely used. The images can be presented on top of each other (Fig.19.5) or side by side (Fig. 19.6). If no equipment is used, cross-eyed viewing is a simple but uncomfortable possibility (Fig.19.7).

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Fig. 19.5 3D tomography images of an oculo-auriculo-vertebral dysplasia patient (see above), mounted for over/under KMQ prism glasses

19 Stereoscopic Imaging ofCraniofacial Malformations

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Fig. 19.6 Close-up of the right condylar region of the same patient, mounted for Lorgnette prism glasses

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Fig. 19.7 Same image pair as in Fig.19.6 mounted for cross-eyed viewing. For spatial perception, the right eye has to look at the left image and vice versa. As an aid, a nger can be placed on the image and then slowly moved

toward the observer, who focuses on the ngertip. When the images in the eld of view of the corresponding eye are congruent in the “perceptual background,” the nger can be removed from the eld of view

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Conclusions

Stereoscopic imaging can be benecial in teaching craniofacial malformations especially if used in an interactive environment. Examination of 3D radiographs and MRI data might also be easier if presented stereoscopically.

References

1. Biddle M, Hamid S, Ali N.An evaluation of stereoacuity (3D vision) in practising surgeons across a range of surgical specialities. Surgeon. 2014;12(1):7–10.

2. Bogomolova K, Hierck BP, Looijen AEM, Pilon JNM, Putter H, Wainman B, etal. Stereoscopic three-

dimensional visualisation technology in anatomy learning: a meta-analysis. Med Educ. 2021;55(3):317–27.

3. Campagnoli C, Croom S, Domini F.Stereovision for action reects our perceptual experience of distance and depth. J Vis. 2017;17(9):21.

4. Julesz B.Binocular depth perception without familiarity cues. Science. 1964;145(3630):356–62.

5. Tauer H. Stereo 3D: Grundlagen, Technik und Bildgestaltung [Stereo 3D: Basics, technology and image design]. 1st ed. Berlin: Schiele & Schön; 2010.

6. Herbig GP. 3 golden rules of stereo photography; 2021 [cited 2021 Dec 20]. https://www.stereoskopie.org/en/

stereoskopie- 2/golden- rules.html.

7. Lipton. Foundations of the stereoscopic cinema. A study in depth; 1982.

8. Wegener C, Jockenhövel J, Gibbon M. 3D-Kino [3D-cinema]: Studien zur Rezeption und Akzeptanz [Studies on reception and acceptance]. Wiesbaden: Springer VS; 2012.

Part IX

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Biological Procedures in Craniofacial

Reconstruction: Distraction Osteogenesis

Craniofacial Tissue Regeneration

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Through Distraction Osteogenesis

ValentinKerkfeld andUlrichMeyer

Introduction

Distraction osteogenesis is a widely used and well-established procedure in maxillofacial surgery to correct bony deformities in a sufcient manner [1]. With the help of distraction osteogenesis, it is possible to replace autologous tissue directly at the site of the defect. Bone can thus be newly formed after completion of growth. The treatment principle can be traced back to the Russian surgeon G.A. Ilizarov, who came across this surgical procedure rather by chance [2]. The procedure was further developed by Snyder and Levine [3] and adapted to the needs of maxillofacial surgery in the 1990s by McCarthy and Schreiber [4]. Today, distraction osteogenesis is indispensable in the correction of craniofacial malformations.

However, the advantage of this procedure lies not only in the formation of new bone tissue, but also in the gradual co-development of the surrounding tissue. In particular, the soft tissue can thus adapt to the new extension in the long term and thus signicantly reduces the potential tendency to recurrence.

Surgical Approach

Distraction osteogenesis can be divided into three different stages based on its timing. First, the bone in question is osteotomized so that an articial fracture gap is created. An anchor is placed at each end of the fragment and connected with a distractor. After osteotomy, the fracture gap should be allowed to rest so that a distractable blastema can develop in it from the hematoma. This blastema is highly vascularized and characterized by a large neoangiogenesis [5]. Now the phase of active distraction follows. In the process, a regeneration tissue (callus) continuously develops at the fracture gap and grows along with it. The length of this phase varies from patient to patient and is determined preoperatively. Finally, the bone and the fracture gap are stabilized and immobilized by the inactive distractor. This consolidation phase is dependent on different factors: distraction length, type of bone, age of patient, and others. Once distraction healing is complete, the distractor can be removed [6, 7].

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

https://doi.org/10.1007/978-3-031-28069-6_20

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V. Kerkfeld and U. Meyer

Physiology ofDistraction Osteogenesis

Physiology ofBone Formation andBone Healing

In principle, the embryonic development of human bone can be divided into three different forms of ossication, which are characterized according to their preformation and force application (Fig. 20.1). These forms of ossication can also be found in adult humans during reparative processes [8–11]:

• The desmal form of ossication is also called

direct ossication, because the bone is formed

directly from the embryonic connective tissue.

This form of ossication is formed when a

tensile load is applied. It occurs in the forma-

tion of the neurocranium, viscerocranium, and

clavicle.

• In chondral ossication, also known as indi-

rect ossication, a cartilaginous skeletal ele-

ment is initially formed (hyaline primordial

skeleton), which gradually remodels into

bone. It is formed by compressive loading. It

can be further divided into enchondral and

perichondral ossication.

– Enchondral ossication is found in the

region of the epiphyseal joints, where interstitial growth causes long bones to increase in length.

– Perichondral ossication is found in the

area of the diaphysis, where annular accumulation of osteoblasts leads to the formation of a bone cuff and nally to the growth in thickness of the long bones.

Bone healing is based on the mechanisms of bone formation considering the mechanical load. The process corresponds to a cascading tissue differentiation. The blood seeping into the defect develops into a hematoma, which coagulates and subsequently forms a brin network. It is then transformed into granulation tissue. For the formation of this granulation tissue, a good blood supply is mandatory. The pluripotent mesenchymal stem cells that accumulate as a result subsequently differentiate either connective tissue under tensile load or cartilaginous under compressive load.

Physiology ofDistraction Osteogenesis

The physiology of distraction osteogenesis is similar to desmal ossication. Due to tensile loading, a steady stimulus occurs that creates cytokine-mediated growth conditions at a cellular and subcellular level. The basic features of distraction osteogenesis are illustrated in Fig.20.2. However, adequate formation of a blastema (soft tissue callus) is important initially.

Fig. 20.1 Different forms of ossication based on their mechanical load

Osteotomy

•Mesenchymal stem cells

Fig. 20.2 Phases of distraction osteogenesis

Resng

•Hematoma

• Angiogenesis

Tensile

load

Compressive

load

Distracon

•Collagen

•Bone columns

Connecve

ssue

Carlaginous

ssue

Consolidaon

•Woven bone

Desmal

ossiﬁcaon

Chondral

ossiﬁcaon

Remodelling

•Lamellarbone

20 Craniofacial Tissue Regeneration Through Distraction Osteogenesis

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263

Since the granulation tissue has only fully developed after about 4days, this phase represents a very vulnerable stage in which a too early or too strong load will lead to failure of fracture healing [5]. In the course of callus distraction, a blastema with many mesenchymal stem cells develops in the fracture gap after osteotomy. These can subsequently be classied into various cells (osteoblasts, chondroblasts, broblasts, angiocytes, etc.) as required [12]. Due to the constant tensile load on the fracture gap, there is a constant stimulus to form new bone. In addition to growth promotion, cytokine-mediated neoangiogenesis is also promoted at the cellular level. Along the distraction vector, increased collagen is produced by the so-called distraction broblasts. By 1 week after osteotomy, vascularization increases markedly, with newly formed small blood vessels also arranged in the vector direction. Histological comparison between a fracture gap without mechanical loading and a distraction gap shows an approximately tenfold increase in vascular supply. Osteons then form on the osteotomized bone fragments, which grow toward each other as they progress. The collagenous bers formed between the bone fragments secrete osteoblasts osteoid and thus give rise to bone columns that grow toward each other in the vector direction. The woven bone formed in the fracture gap remodels into lamellar bone under functional loading [13].

Biomechanical Considerations

The treatment success of distraction procedures is inuenced by various factors. The bone anatomy and biomechanics as well as the distraction forces are decisive for healing. Mechanical loads on the osteotomized bone fragments trigger certain biological reactions that are decisive for the success of the treatment [14–16].

Bone Mechanics

Distraction osteogenesis has a manifold biomechanical effect on regenerating bone tissue, creating a process that is still not fully understood because of its complexity and dynamics [17]. Bone deformation is signicantly inuenced by

two factors: anatomy (micro- and macroscopic) and mechanics (elasticity and compression). Furthermore, external conditions, such as force transmission through surrounding tissues (joints, ligaments, muscles, and soft tissues), have an inuence on bone deformation. These inuences result in the tissue microenvironment in intact bone or callus (Fig.20.3).

Principles ofLoad-Related Bone Regeneration

In principle, the function of a bone is to provide structural strength oriented to mechanical loading. Accordingly, the bone should have such mechanical strength that no bone injuries (fractures) are caused by usual loads. Studies also show that bone tissue can adapt to different mechanical conditions [18, 19]. In this context, load-dependent signals regulate the modeling [20]. So-called basic multicellular units (BMUs) play a decisive role in this process. Accordingly, hormones bring about only a 10% change in bone strength in the postnatal phase, while 40% of the effects are due to mechanical inuences.

Bone remodeling occurs physiologically through simultaneous bone resorption and bone formation. BMUs remodel bone into small packages. If an activating event now follows, some bone resorption occurs, which is followed by new bone formation [21, 22]. The BMU-based model recognizes two states: “conservation mode” and “disuse mode” [23]. Depending on the load, one of these states is activated [22].

Mechanotransduction ofOsteoblasts

Tensile stresses represent the major stimuli in distraction osteogenesis [24]. It is generally assumed that cellular deformations induced by distractions reach the cellular genome via the mechanotransduction pathway. Mechanotransduction means the conversion of a physical force to a cellular response. This represents an important mechanism in bone regeneration [20]. This allows bone tissue to adapt to different environmental conditions and respond to mechanical stimuli. Mechanotransduction can be divided into four different mechanisms:

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Fig. 20.3 Different biomechanical inuences of distraction osteogenesis. (Adapted from Meyer, Kleinheinz [1])

V. Kerkfeld and U. Meyer

Tissue environment

Force

Tissue

envelope

Joints

Ligaments

Muscles

So ssue

Bone deformaon

Anatomy

Macroscopy

Microscopy

Mechanics

Elascity

Compression

1. Mechanocoupling (the force acting on a tissue is translated into a local mechanical signal that acts on the bone tissue)

2. Biochemical coupling (a local mechanical signal triggers gene expression or protein activation)

3. Transmission of signals (the produced signal is transmitted to the effector cell)

4. Effector cell response (which leads to bone formation or degradation)

When tissue is mechanically stressed, the tis-

sue deforms and causes strains (10,000 strains ≙ 1% change in length). Sensors for these length changes are osteoblasts and osteocytes, which are distributed in the bone structures to monitor and detect these mechanical changes.

Distraction Histiogenesis

One advantage of distraction osteogenesis is the simultaneous expansion of the surrounding soft tissue (distraction histioneogenesis) in the direction of distraction. In contrast to the bony processes, no tissue is severed here, but merely gradually stretched. In principle, two different reactions to the stretching stimulus can be distinguished:

• Reparation in the case of tissue rupture

• Histioneogenesis due to growth (hypertrophy and hyperplasia)

Different tissues respond differently to the

same stretch stimulus. For example, connective tissue exhibits good resilience to stretch and responds with growth. This contrasts with nerve

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