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 Table of Contents  
Year : 2021  |  Volume : 38  |  Issue : 3  |  Page : 187-193

Application of the life-size patient-specific three-dimensional cervical spine anatomical model for odontoid fracture fixation

1 Department of Neurosurgery, Faculty of Medicine, Ege University, İzmir, Turkey
2 Department of Anatomy, Digital Imaging and 3D Modelling Laboratory, Faculty of Medicine, Ege University, İzmir, Turkey
3 Department of Radiology, Faculty of Medicine, Ege University, İzmir, Turkey
4 Department of Physical Therapy, Faculty of Medicine, Ege University, İzmir, Turkey

Date of Submission05-Sep-2020
Date of Decision15-Dec-2020
Date of Acceptance18-Dec-2020
Date of Web Publication20-Sep-2021

Correspondence Address:
Erkin Ozgiray
Department of Neurosurgery, Faculty of Medicine, Ege University, TR-35100, Izmir
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/nsn.nsn_160_20

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Objective: Cervical fixation is the most common treatment of vertebral fractures, osteosarcoma, osteomyelitis, arthritis, and congenital disorders. Mortal complications, such as internal carotid artery, vertebral artery (VA), and spinal cord damages, may occur during the application. The aim of this study was to create the application of the actual three-dimensional (3D) personalized model which was exercised for screwing insertion in C2 damage patients. Methods: Two patients with Type II of C2 fractures were treated with personalized spine models. These models were investigated to achieve particular information of non- and bony elements such as the highness, thickness, and the field of pedicles and vascular diameters for an intraoperative reference. The model was to determine the probable variations and to observe the success of screw rate in the treatment of C2 fractures. The operation duration, instrumentation time, blood loss volume, and clinical and radiological assessment were done. The 3D model's perception was evaluated. Results: Cervical models were defined to secure intervention areas of the VA pedicles and screws. Neither vascular nor neurologic damages were happened in all cases. Besides, the cases did not include broken nails, screw pullout, fracture of bone structure, or infection. Cervical models demonstrated (1) examination of the VA pattern, (2) valuation of virtual screw trajectory line before screw fixation, (3) the application of prebent rods during procedure to contribute to the safety of the posterior instrumentation, (4) postsurgical confirmation, and (5) examined movements of the neck postoperatively. The perception of 3D model for treating C2 fracture was thereby diminishing surgical time, bleeding amount and operative complications. Survey perception of model was calculated in statistical significance (P < 0.05). Conclusion: Personalized model is active and confident in achieving an accurate and safe screw fixation during surgery, especially in anatomically abnormal cases. Cervical model provides an accurate representation of the fracture location, pedicle size, and VA shapes. It is therefore useful in surgical planning as it maximizes the possibility of ideal screw position, as well as providing individualized information concerning cervical spinal anatomy.

Keywords: Individualized screw insertion, odontoid fracture, patient-specific model, preoperative planning, vertebral artery

How to cite this article:
Ozgiray E, Özer MA, Şirintürk S, Gùvsa F, Dursun E, Eraslan C, Hepgüler S. Application of the life-size patient-specific three-dimensional cervical spine anatomical model for odontoid fracture fixation. Neurol Sci Neurophysiol 2021;38:187-93

How to cite this URL:
Ozgiray E, Özer MA, Şirintürk S, Gùvsa F, Dursun E, Eraslan C, Hepgüler S. Application of the life-size patient-specific three-dimensional cervical spine anatomical model for odontoid fracture fixation. Neurol Sci Neurophysiol [serial online] 2021 [cited 2022 Jun 28];38:187-93. Available from: http://www.nsnjournal.org/text.asp?2021/38/3/187/326287

  Introduction Top

Posterior instrumentation is needed for the treatment of cervical instability which usually leads to odontoid fractures, cervical subluxation, trauma, tumor, infection, rheumatoid arthritis, and congenital malformations.[1],[2],[3],[4],[5] Many studies on the anatomy of C2-C6 area have described several techniques for inserting screws into the cervical spine.[2],[6],[7],[8],[9] The application of this procedure is affected by various factors such as complex anatomical detail including the internal carotid artery, vertebral artery (VA), nerve roots, cervical curvature, and articular surfaces.[5],[9],[10],[11],[12] On the other hand, upper cervical spine posterior instrumentation is still challenging owing to the surgical difficulty of the cervical area, hemorrhage from the venous networks, and damage to the hypoglossus nerves, VA, and C2 and C3 nerves. Especially, VA damage could be critical as it has the potential to lead to severe complications during posterior instrumentation because of its adjacent relation with the entrance point and path of the screws (0%–16.7%).[9],[13],[14],[15],[16]

Given the unique structural details of the craniovertebral junction and cervical curvature, proper pedicle screw placing can be challenging with increased surgery time and potentially increased damage rate. This could lead to a poor outcome, especially in aberrant VA course, pedicle hypoplasia cervical kyphosis, and old patients with cervical vertebral fractures.[4],[5],[9],[10],[12] Complex odontoid fractures represent traumatic injuries to the upper cervical spine for which the best method of treatment is unknown. The importance of this variability in fixation in a clinical case is unknown, especially for C2 fracture [Figure 1], ][Figure 2], [Figure 3], [Figure 4]. In such cases, data for patient-specific fixation are required. It is crucial to evaluate to what extent the patient can manipulate the neck after screwing.
Figure 1: Preoperative computed tomography examination scans at sagittal (a), frontal (b) view, case with fracture (arrow) at C2

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Figure 2: Visualization of the stereolithographic files craniovertebral junction with odontoid fracture (thick arrow) and cervical misalignment (red angle) (a), and to remove superimposition of the C1 allowing inspection from odontoid process (b), ponticulus posticulus (thin arrow) (c)

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Figure 3: Dimensions of X, Y, Z for three-dimensional patient spesific life-size cervical column stereolithographic file

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Figure 4: Visualization of the relationship between vascular and bony structures of the cervical column in made of polylactic acid printed model

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Three-dimensional (3D) models have been reportedly applied in many surgical areas such as orthopedic, facial and vascular procedures.[8],[17],[18],[19] New advanced technology creates a life-size 3D cervical spinal model based on CT digital imaging.[20] Using 3D models assists in the planning of complex surgical interventions such as screw fixation of posterior instruments and make their insertion easier.

Personalized modeling is essential as each patient has a special anatomical build. To keep away serious complications such as spinal cord and VA injuries during posterior instrumentation, correct operative planning and attentive intraoperative procedures are essential, including the use of a navigation system and/or a full-scale 3D model. In this study, we report a master plan that maximizes the usefulness of the personalized model by recognizing visualization of the VA relation to the cervical spine and presurgical screw insertion into the model, observed by radiographical analysis of images of the model. Here, we aimed to create the application of patient-specific actual models prior to the operation of the patients with upper cervical fixation. In the current study, it was aimed to create a 3D life-size model of patients by considering the presence of a solid fracture model in the hands of the surgeon, examining the fracture lines from every angle and being more effective in preoperative planning. In the current study, we investigated the surgical outcome of the exercise of digitally designed C2 fractures for assisting pattern to put plates and screws for the intervention of cervical breaks.

  Methods Top


C2 fractures were determined in two cases who pealed to the hospital with condition of severe neck pain and apathy due to car accidents [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]. The study was approved by the suitably constituted Ethical Committee at Research Department of Ege University (17-6/19), within which the work was undertaken, and the study conforms to the Declaration of Helsinki.
Figure 5: Allowing inspection from backside C1, C2 in polylactic acid printed model

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Figure 6: (a and b) Cases that have undergone posterior occipitocervical fixation, postoperative computed tomography scan images

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Figure 7: Preoperative model (a) to remove superimposition of the C1 allowing inspection from odontoid process (arrow), and cervical misalignment (red angle) (b), postoperative model with screw positions of posterior screwing (red curve) (c) and osseous graft (black star) (d)

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Imaging studies

The cases underwent plain X-ray, computed tomography (CT) angiograms, and dual magnetic resonance imaging to detect location and the type of odontoid fracture. All cases had in the base of odontoid as Type II for Anderson-D'Alonzo classification [Figure 1]a, [Figure 1]b, 2a, [Figure 2]b and [Figure 7]a. Pre / post operative scans including vessels and patency of VA [Figure 2]c; in post-operative examinations, the localization of the screws was examined [Figure 6]a and [Figure 6]b.

Three-dimensional printing model

Patient-specific actual models were created for presurgical planning of the screw operations to safe and perfect upper cervical fixation. CT scans were converted into DICOM format [Figure 2]a, [Figure 2]b and [Figure 3]. The 3D models of cervical column were designed in each case through the integration of their dual resolution CT with a rendered model (3D Slicer version 4.5.0-1 r24735). After a 3D model had been generated, the model was printed using a Mass Portal [Figure 3], [Figure 4], [Figure 5] and [Figure 7]. Bony elements such as the spinal canal, transverse foramen and the distance from the midline to the transverse foramen, and the height and the area of pedicles were studied in the 3D cervical spine models [Figure 4] and [Figure 5]. Distance from midline to transverse foramen and height and area of pedicles were appeared in the models. Nonbony elements such as the variations of the course of the VA and the relationship between the bones were defined [Figure 4] and [Figure 5].

3D models of the cervical spines were created preoperatively with the odontoid transverse fracture and postoperatively with the screwed vertebras (1:1 model) [Figure 7]a, [Figure 7]b, [Figure 7]c, [Figure 7]d. Hence, these models were created basing on the data of 1:1 cases, the presence of the osseous bridge of the C1 (ponticulus posticus) and VA, enabling operators to understand better the measurements and place of the screw in relative to adjoining tissues [Figure 2]c and [Table 1]. Screw fixations were planned and made based on the real-life models. Reference landmarks had been targeted for presurgical planning of the instrumentations to maximize sure and apply cervical fixation of the fractures [Figure 7]a and [Figure 7]b. The post-operative scanning facilitated the evaluation of the created models of vessels involved, the pattern of VA, and the position and the condition of the screwing [Figure 6]a and [Figure 6]b. The preoperative planning and postoperative controlling of screw postures, adaptation, plate location, and size of screws and distances of screws were studied to determine in 3D life-size models.

Screwing surgery

Patients were intubated and put in prone position. A midline suboccipito-cervical skin incision was performed following a routine preoperative preparation. Suboccipital and cervical muscles were retracted bilaterally exposing the occiput and posterior elements of the C1–7. C2 transpedicular and C3–6 lateral mass screws were placed under C arm visualization. Occipitocervical plate was fixed following the screw placement. Appropriate decompression was performed via C2–3 laminectomy. Following the final control under C-arm, the layers were closed. The operation duration, instrumentation time, blood loss volume, and clinical and radiological assessment were done.

Evaluation the three-dimensional model's perception

Resident doctors were asked to answer the questionnaire by examining the radiograph, the CT image, and the 3D model of the C2 fracture cases [Figure 8] and [Figure 9].
Figure 8: Perception working mechanism with the radiograph, the computed tomography image and the three-dimensional model

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Figure 9: Resident doctors have more positive perceptions about three-dimensional model

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Statistical analysis

The data were analyzed using Student's t-unpaired, Chi-squared test, and Friedman test. Statistical analyses were performed using SPSS version 25.0 software (IBM Corp., Armonk, NY, USA). P < 0.05 was considered statistically significant.

  Results Top

Preoperative planning

The 3D printing technique helped create actual models that assist the surgeon to observe the anatomy from any direction [Figure 4], [Figure 5] and [Figure 7]a and [Figure 7]b. The models can be perceived and measured in detail [Table 1]. Bony factors of spinal canal, transvers opening, and area of pedicles were demonstrated. The axes of C1 and C2 were not in the same plane [Figure 7]a and [Figure 7]b. Anatomic variations of C1 and C2 such as ponticulus posticus were demonstrated [Figure 4], [Figure 7]a and [Figure 7]b.

Intraoperative findings

Total surgery time for the case one was 250 min as was 340 min for the case two. Time consumption for each screwing was calculated as 62 min and 42 min, respectively. Total blood loss was recorded as 280 and 550 ml for cases one and two. However, to have the opportunity to experience in situ screwing prior to the operation enabled a complication free, safe, and fluent surgery.

Postoperative findings

Postoperative radiograms depict the proper screw alignment in each trajectory. With postoperative verification, the damage resulting from biomechanical screw malpositioning and rigidity of the screwing in the cervical region on anatomical structures was evaluated [Figure 7]c and [Figure 7]d. The [Figure 7]d shows the bone graft. Modeling has also aimed at evaluating the postoperative life quality of the patients' neck movements and their neck angles [Figure 7]c. Postoperative CT scan showed that the operation yielded satisfactory results [Figure 6]a and [Figure 6]b.

Rehabilitation was initiated 1 week postoperatively. The patients' pain decreased from 9 to 6 according to the visual analog scale (VAS) (0–10). It was tried to reduce too much spasm in neck muscles of patients. Muscle strength of shoulder muscles was 3, and elbow muscle strength was scored as 4. The patient was started on analgesic, myorelaxant, and antidepressants. As a result of the rehabilitation, the patient had a flexion of 30°, extension of 0°, lateral flexion of right and left 5°, a right rotation of 7°, and a left rotation of 5°. The pain was two times higher than the VAS. Muscle spasm decreased. Neck flexion muscle strength was evaluated as 4. Shoulder muscle strength was 4 and elbow muscle strength was 5.

The three-dimensional Model's perception

In the study, the Cronbach alpha coefficient calculated for reliability was found to be 0.86. Based on this result, it can be said that the survey is reliable. Friedman test was applied to compare the perceptions of the residents on the radiograph, CT, and 3D patient-specific models [Figure 8]. A statistically significant difference was found between the perceptions of resident doctors (P < 0.05). Resident doctors have more positive perceptions about 3D model [Figure 9]. Resident doctors stated that they found a 1:1 solid model useful. These benefits include; making the preoperative planning easier, preparing the intervention needed, shortening the operation time, reduction of bleeding amount, deciding the plate size and screws more definitely.

  Discussion Top

Screw insertion in occiput-C6 poses a tremendous defiance to the surgeon due to the course of VA variability, the curve of the vertebras, osseous variations, and the variable size of the small pedicles.[3],[10],[21] The most common complications reported include misplaced screws, VA insufficiency, neurologic complications, cerebrospinal fluid leakage and infections. Inexperienced surgeons have been tried to have a higher hazard of leading VA failure, screw misplayed positions (5.7%–8.8%), neurologic deficit (2.3%–4.3%), or required another operative revision or extractions of screws.[12],[19],[21],[22],[23]

The odontoid fixation is a challenging procedure, particularly in variable structures with patients affected by bone shapes [Figure 7]a, [Figure 7]b, [Figure 7]c, [Figure 7]d and includes screw positioning close to the vital structures.Risk agents for iatrogenic arterial hazard following posterior instrumentation include injured or deficient pedicles from a rheumatoid arthritis, incomplete reduction of screw placement, failure to recognize a variable VA course.[8],[12],[13],[24] The relationship of the internal carotid artery and the hypoglossal nerve, which are anatomically just a few millimeters over the anterior aspect of the lateral mass of the C1, must be acknowledged. Intrasurgically, the internal carotid artery can be evaded with an inferiomedial way of the axis screw.[11],[25]

In doubt, a unicortical obtain might be adequate to install stability.[6],[16],[23],[26] If the heads of the screws stay after the hypothetic red dotted line, which is behind the posterior rim of the C2 vertebral body, a VA damage is unlikely to occur [Figure 4] and [Figure 5].

Prior to the operation, in order to minimize possible complications, the ideal procedure should be the utilization of individualized measurements and screw with proper equipment.[8],[22],[27] The surgery team prepares and plans the surgery in advance with personalized modeling. The measurements of angle should be calculated correctly [Figure 7]b and [Table 1]. Bony and nonbony elements should be evaluated properly. Previous researches have defined adaptation points and targetional intervention angles for cervical screwing. In these researches, pictures of cervical region were used mainly. Limited pictures of carotid and vertebral arteries had incorrect measurements. This study provided all details related with the case with an actual modeling. Probable risks of instrumentation and right measurements were stated with anatomical 3D model.

The use of preoperative models serves better understanding of the lesion and can lend to the preplanning of the surgery.[9],[11],[24],[27],[28] Handling the model exposes the cervical region to the surgeon in every aspect. The surgeon and the team will be more familiar with the unique anatomy and the pathology prior to the surgery. The relation of the vertebral canal, transvers openings and the guidance of pedicles may be simulated in the surgeons' mind with more precision [Figure 2]a, [Figure 2]c, [Figure 4], [Figure 5] and [Figure 7]b. Furthermore, variations of the VA, detected up to 20% of the cases, requires a thorough presurgical view by CT angiogram and also an attentive preplanning of the screw line in order to reduce the hazard.[2],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23],[24],[25],[26],[27],[28] This technique provides a reliable reference for surgical preplanning.

In this study, we positioned the screws in a real size patient model with control of an anatomical specimen. Nevertheless, we trust that our findings may be transferred to our neurosurgical routine because the evaluation of the screw plotting is an outcome of the personalized anatomy of the cervical vertebral column which should be indicated by CT data. Dual energy is used in cases where modeling will be applied for the imaging as the images do not have a beaming like a flash. However, they can service as an important component tool to achieve a better sensibility the structure in a life-like model, especially in complicated and stringent cases.

In our study, the personalized modeling of the standard path in two patients with no aberrant VA run permitted a safe screw placement, which protected the VA canal. The input spot for the C2 screw was the cranial and medial quadrant of the C2 in line with the path of the pedicle. The screw path was sited approximately 20° to 30° medially and in the cephalad direction along the C2 pedicle. The model with C2 fracture very well shows the specific place and violence of the fracture and the facet of dislocation. In one patient, unilateral ponticulus posticus was detected. We believe that it is almost unfeasible to change the way completely by individual needs during the procedure. All of 10 screws of each person were shown to be standed correctly as they were designed. The study is not designed as a correlative one and it does not include data from any other case performed without guidance of a 3D modeling. However, comparing to extensive volume of previous cases which are not included in this study, both time consumption and blood loss are not above average.

Patient-specific model survey's benefits include; making the preoperative planning easier, preparing the intervention needed, shortening the operation time, reduction of bleeding amount, deciding the plate size and screws [Figure 9]. The models were sterilized and used during the procedures to support surgeons, which were supplied more natural information. The models assisted the residents pick the screw entrance point, way of the screw, length of the screw, and secure the correctness of screws.

The deficit of 3D technology was almost 4–10 h must be taking on producing the actual model. So that, this surgery cannot be used for cases who must to require an operation.

Some limitations could be noted in this study. It was a randomized noncontrolled blinded study and concentrated on the intraoperative outcomes rather than long-term clinical benefits. Currently, the use of 1:1 patient models supports not only preoperative planning but also practicing and education. Besides, these models can be implemented for cases with odontoid fractures and helps to explain their families the condition of the patient, surgical procedures and possible risks.

  Conclusion Top

The 3D model is helpful in the preplanning and intraoperative accuracy of screwing procedure, and post-operative verification, especially in C2 fracture patients with anatomical variations. A 3D patient specific model can aid the surgeon to see the fracture patterns better than two dimensional CT slices, to anticipate the operative complexity, and choose the safest surgical approach and specific instruments required for the operation.

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Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]

  [Table 1]


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