Anomalous Craniovertebral Junction (CVJ) Anomalies in Pediatric Population: Impact of Digital Three-dimensional Animated Models in Enhancing the Surgical Decision-making.

The challenges and complexity in the management of pediatric craniovertebral junction (CVJ) anomalies lie in the difficulty of precisely diagnosed the CVJ instability in this age group, followed by strategizing the fusion method. Three aspects are essential to incorporate in the management algorithm of pediatric CVJ anomalies. The first is developmental, consisting of separation and resegmentation of the spinal column at the CVJ which requires that the age-dependent ossification process of the cartilaginous part of C1 and C2 be understood to enable an accurate diagnosis based on computed tomography (CT) and magnetic resonance imaging (MRI), especially in infants and children less than 6 years old; second, because the CVJ is the most mobile part of the spinal column, assessment of the functional anatomy via CT/MRI-based dynamic motion studies is often critical to revealing the pathogenesis of CVJ lesions. The third aspect is the understanding of the bony anatomy of the CVJ is a crucial prerequisite to optimal planning of surgery. These intricate anatomical understanding may be simplified by using preoperative 3D digital animated models.

The clinical application of visual three-dimensional (3D) software animations is rising in the medical field in the recent era.[123456] Access to cadaveric laboratories is limited nowadays. Therefore, the virtual software offers a cost-effective educational resource. The editorial provides proof of the concept that how the utilization of simple software application for 3D visualization in the preoperative period during surgical management of pediatric CVJ anomalies can turn the highly intricate CVJ pathology to a simpler one by helping to understand the biomechanics and developmental anatomy. It became a trend changer in the surgical filed of CVJ. The unique advantages of reusability, multi-angle specimen observation, and nondestructive virtual anatomy give an edge to digital 3D animated model technology.

DIGITAL 3D ANIMATED MODEL: AN ADVANCE EDUCATION TOOL

It is imperative to master the aberrant anatomy of CVJ in case of developmental or syndromic anomaly.[789] The ability to conceptualize and anticipate the preoperative radiological findings in the 3D hypothetical image, usually comes by experience. This capability or potential is different among the surgeons and necessitate a learning curve. The learning curve of each surgeon is unrelated and depends on several factors. However, with the introduction of 3D simulation models like 3D printing, saw-bone models, and new digital 3D models, one may curtail his learning curve and also offer better and safe surgical outcomes. Among these three, the digital 3D model is cheapest, widely available, reproducible, and most accessible to depict the slightest variation from normal anatomy. These 3D computer-based software models enable the surgeon to rotate virtual vertebral bodies and understand the spatial relationships. The new versions of Macintosh Operating System (IOS) have in-built software in Powerpoint/Office programs compatible with magnetic resonance imaging (MRI) viewer. Using this software, one has to upload the MRI or computed tomography (CT) scan of the patient and generate a virtual image. The software can not only measure the size of pedicles, a distance of vertebral artery from affix, or standard screw entry points, but the visualization tools may also be used for scrolling or zoom-in-out the image.

Therefore, the interpretation of complex CVJ anatomy and safe screw trajectory in the background of the anomalous vertebral artery course converts much easier for surgical planning. The models are also an excellent method for teaching purposes, being easily reproducible and has a wide projection. The standard cadaver system of teaching is expensive and challenging to translate on a pediatric patient of CVJ anomaly. Goel et al. showed that the digital 3D software models stipulate a dynamic display of multiple orientations.[3] Nguyen et al. also showed that learning human anatomy is influenced by the interaction between the learner’s spatial ability and the dynamism and interactivity of the instructional tool.[5] Therefore, a simple 3D software tool delivers a worthy opportunity for young surgeons in their initial learning curve period.

CONCEPTUALIZATION OF 3D C1–C2 DISLOCATIONS BY 3D MODEL

One must conceptualize the dislocation in three dimensions and understand the pathological biomechanics in all the three planes. Our prior publication describes six types of dislocations, most common one is the combined type of C1–C2 dislocation in all three axes; i.e., the amalgamation of translational dislocation [increase in atlanto-dental interval (ADI) >4.5 mm in pediatric age]; presence of basilar invagination; and coronal tilt and rotational dislocation altogether.[10] The digital 3D animated models exactly postulate this information and enlighten the surgeon in the better surgical decision. The capability to rotate the animated model, highlight the anomalous anatomy, and measure the vertebral part’s width assists the neurosurgeon. Some of the case illustrations are described with various types of C1–C2 dislocation, which is planned by the help of a 3D animated model for optimal correction [Figures 1–7].

Figure 1

A 6-year-old male child with reducible AAD (type 1-C1-C2 dislocation): translational dislocation without BI or rotatory dislocation/coronal tilt. As facet joint orientation is flat and symmetrical on both the side, only manual reduction can be enough to require to AAD reduction and followed by fusion by C1–C2 lateral mass screw and rod was planned

Figure 7

Digital animated 3D model of a patient with CVJ anomalies with vertebral artery anomalies. It helps to define the third part of vertebral artery size and course (red in color). Image showing the normal course of vertebral artery; occipitalized Atlas with an anomalous entry of VA in congenital occipitalized foramen and persistent intersegmental artery which cross the C1–C2 facet joint leads to an increase in the risk of injury during instrumentation

A 5-year-old male syndromic AAD (chondrodysplasia punctuate); type 1 C1–C2 dislocation, subaxial cervical kyphosis due to C2/C3 vertebral body hypoplasia with reducible AAD. With the help of an animated model, we can access the CVJ development, particularly the development of lateral mass and lamina. In this child occipito-C4 long segment, fusion was performed for cervical instability

A 16-year-old male with Type II C1–C2 dislocation which is defined as central dislocation or BI (Goel group B type BI) that consisted of pure basilar invagination with a normal atlantodental interval associated with Arnold Chiari malformation. 3D animated clearly showing subtle C1–C2 subtle facet posterior dislocation demands C1–C2 fusion

A 10-year-old male with Type III dislocation. Defined as translational with central dislocation (BI) without rotatory dislocation/coronal tilt. 3D digital model showing symmetrical facet joints on both the side can be planned for reduction of BI by distraction with spacer and C1–C2 fusion

Type IV dislocation, defined as translational and rotational dislocation with coronal tilt but without basilar invagination. Bilateral asymmetrical facet joints (one side vertical and another side oblique) cannot allow the smooth reduction of AAD by C1–C2 distraction with spacer, rather atlantodental interval and rotation may increase during distraction due to spacer application between this asymmetrical joint. The neurological deficit may worsen due to a reduction in critical diameter

A 8-year-old male child with Type VI dislocation, which is a combined type of dislocation, that is, translational, central, and rotational dislocation with coronal tilt

CLINICAL APPLICATION OF NOVEL DIGITAL 3D MODELS IN PEDIATRIC NEUROSURGERY PRACTICE

Precisely pinpointing the developmental stage of CVJ

Developmental anatomy demonstrates age-dependent mechanisms and the pathophysiology of pediatric CVJ anomalies.[11] At a younger age, the atlantoaxial instability is mostly reducible. Menezes describes the sequence of events, in the process of progressive vertical dislocation of facet joints in the posterior fossa, pannus forms around the odontoid process, till this age, C1–C2 instability (the process of odontoid invagination into the foramen magnum) is still reducible but progressive. However, as the child grows, grooving occurs behind the occipital condyles secondary to upward migration of the axis vertebra, which makes it irreducible at 14 to 15 years of age. Moreover, the protective cervical muscle muscles are relaxed or inadequately developed, as, in the case of a young child under general anesthesia, the craniovertebral junction becomes inherently less stable than that in an adult.[12] Thus, before 14 years of age, traction will help to reduce the majority of irreducible AAD and BI due to the laxity of ligaments of CVJ and muscle relaxant effect with general anesthesia. Dynamic 3D reconstruction helps in to recognize the factors responsible for irreducibility like supernumerary facet joints, asymmetrical facet joints, and very high BI with rotational dislocation.

Morphological analysis of C1 lamina suggested that the diameter of C1 lamina reached approximately 4 mm by 4 to 6 years of age.[13] Likewise, the width of the pedicle and lateral mass of C2 becomes more then 5 mm after 2 years of age, in that case, the use of a 3.5-mm lateral mass and pedicle screw in 2- to 6-year-old children was feasible in the majority of cases but with caution to prevent the inadvertent entry into vertebral artery groove in a patient with anomalous C2 lateral mass hypoplasia or narrow isthmus.[14] During the developmental stage in the ossification process, by synchondrosis of C1 and C2 arch, both the side of arches fused in the midline and become 5 mm in width at 6–7 years of age. That is why we prefer to apply a horizontal connector between two side rods to provide maximum stability, especially in the rotational movement of the cervical vertebra. Thus, the 3D model helps into the assessment of the development of lamina, lateral mass as well as pedicle width to preoperatively plan the need for a particular screw size and surgical method of fusion technique.

The Bony fragility and maturity are variable with the ossification stages of CVJ. In developing age, the ossification of the cartilaginous part of CVJ was completed at around 5 to 7 years of age. Before 7 years of age, any CVJ instability, whether it should be considered as occipito-cervical instability or only C1–C2 instability, is quite dubious. We consider it occipito-cervical instability and prefer occipito-cervical fusion rather than only C1–C2 fusion below 5 years of age. Another typical indication of occipito-cervical fusion is AAD, BI, with occipitalization of Atlas where very high BI, anomalous C1 lateral mass anatomy, and anomalous course of VA crossing the C1–C2 joints preclude the C1 lateral mass fixation. In such a case, occipito-C2/C3 fixation after distraction would help to prevent vertebral artery injury; moreover, as C1 is occipitalized, the biomechanics does not affect whether you do C1/2 or occipito-C2 fixation. The 3D model’s assistance meticulously evaluates not only the facet joints’ symmetricity but also the vertebral artery anomalies and course related to C1/C2 joints. Thus, the preoperative selection of the C1/C2 fixation vs occipito-cervical fixation can be determined.

Understanding the vertebral artery anomalies related to C1/C2 joints

The 3D animated model helps define the precise bony and VA variations that may be responsible for heightened intraoperative risk. We have classified the vertebral artery congenital variations in the third part of CVJ and established the scoring system based on various vertebral artery anomalies and its implications to prevent the VA injury during C1/C2 screw fixation.[15] It helps to choose the appropriate surgical technique of posterior stabilization based on the preoperative location of VA relative to the C1–C2 facet joints.[15] The anatomical variations include the presence of a persistent first intersegmental artery, a fenestrated VA, or a low-lying PICA: An anomalous medial deviation of the third segment of VA; a high-riding VA with a narrow C2 isthmus; a rotational deformity or a tilt at the occipital-C1–C2 level that again resulted in a medial deviation of VA; and unilateral dominance of VA. The intracranial course of the VA, especially in the third part, can be precisely defined via the preoperative 3D animated model [Figure 7]. Objective risk stratification of the VA helps in significantly reducing its chances of injury during pediatric CVJ surgery.[15]

CONCLUSION

The advent of highly advanced radiological investigational tools like the 3D animated model embarks the new revolution in pediatric CVJ surgery. Translating a CVJ anomaly in the three-dimensional virtual image is an art, which comes by experience. The understanding of 3D congenital C1/C2 facet joint dislocation, symmetricity of the joints, and precise developmental age helps in the correct diagnosis of CVJ instability in pediatric age. It helps in optimal and safe surgical correction of the instability by accurate planning.

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Conflicts of interest

There are no conflicts of interest.