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Back to Journal »International Journal of General Medicine» Volume 14

The feasibility of anterior occipital condyle screw reconstruction of the cranial vertebral junction: a new technique of digital anatomy and cadaveric study

Authors: Xu De, Peng Yan, Li Hua, Wang Yan, Ma Wei

Published on September 8, 2021, the 2021 volume: 14 pages 5405-5413

DOI https://doi.org/10.2147/IJGM.S332071

Single anonymous peer review

Editor approved for publication: Dr. Scott Fraser

Dingli Xu, 1 Yujie Peng, 2 Haojie Li, 2 Yang Wang, 2 Weihu Ma 2 1 Department of Orthopedics, Affiliated Hospital of Ningbo University School of Medicine, Ningbo, Zhejiang; 2 Department of Spine, Ningbo Sixth Hospital, Ningbo City, Zhejiang Province, People's Republic of China Corresponding author: Zhonghua Ma Weihu Spine Department, Ningbo Sixth Hospital, Ningbo City, Zhejiang Province, People’s Republic of China Email [Email protection] Background: Anterior occipital condyle screw (AOCS) may be a viable alternative technique for reconstruction of occipital-cervical fusion at the cranial junction Surgery. This study aims to analyze the feasibility of AOCS. Methods: The computed tomography (CT) scan results of 40 adults at the cranial vertebral junction were included and imported into Mimics software. Then, a three-dimensional reconstruction digital model of the cranial-vertebral junction was established, and the entry point, insertion angle and screw trajectory were determined. After the AOCS inserted ten human cadaver spinal specimens, a CT scan was performed to verify the position between the screws and important structures. Results: The best entry point is located at the caudal and medial ventral side of the occipital condyle. The best trajectory is the inclination angle of the sagittal plane (5.9°±3.4°) and the divergence angle of the axial plane (26.7°±6.0°), and the screw length is about 21.6±1.2mm. In any specimen, no screws invaded the sublingual canal and vertebral artery. Conclusion: AOCS fixation is a feasible and novel anterior cranial vertebrae junction reconstruction technique, which can be used as an effective alternative to the anterior reconstruction of the titanium mesh cage. Keywords: anterior occipital condyle screw, cranial reconstruction, optimal approach, cadaveric study

The cranial vertebral junction (CVJ) that connects the spine and the skull base is a key structure because it is a complex combination-bony and ligaments, which have two functions, supporting a greater degree of movement and allowing biomechanical stability sex. 1 However, there are some diseases that cause CVJ death and disability, such as rheumatoid arthritis, tuberculosis, malformations, trauma, infections, congenital malformations and tumors. These diseases can cause cranial nerve dysfunction, limb paralysis, spinal cord disease and even death. 2

When CVJ is unstable or spinal cord compression is caused by these dangerous diseases, occipitocervical fixation and reconstruction should be performed. 3 Generally, rod/wire, rod/screw and plate/screw fixation are widely used for posterior occipital-cervical fusion, such as Luque rod-wire fixation, 4 occipital plate fixation. 5 Visocchi et al. reported that of 9 adult patients with unstable craniovertebral junctions who underwent posterior occipitocervical fusion, 8 patients had improved neurological function without complications. 6 and similar articles reported posterior occipital fusion. Neck fusion can achieve satisfactory and high bone fusion rate. 7,8 Adverse events of posterior occipital-cervical fusion have also been reported, including vascular injury, cerebrospinal fluid leakage, tectorial injury and even failure of fixation. 9,10

For the anterior treatment of occipital-cervical fusion, there have been reports of total spondylectomy using a combined approach 11 and reconstruction using a ramp plate and a titanium mesh cage. 12 Although these two methods can ensure immediate fixation and satisfactory bone fusion, many reported complications include new neurological deficits, implantation failure, cerebrospinal fluid leakage, and cervical nerve root injury. 13,14 The ramp steel plate with the titanium mesh cage invades the skull, so there is no need to study for a long time and practice a lot. 15 Therefore, optimal internal fixation allows for stronger support and safe insertion.

Therefore, the occipital condyle is a hot spot and is considered a feasible anchor point in the reconstruction of the cranial junction. Zhou et al. reported a CT-based method for morphometric analysis of 27 fresh frozen human cadavers. They concluded that the occipital condyle can safely fix a screw with a diameter of 3.5 mm. 16 Tong et al. reported that they used the occipital condyle-C1 compound screw in 8 patients with basal ganglia depression. The screw was not misaligned or positioned incorrectly on the CT scan, and no neurovascular complications were detected during follow-up. 17 These studies indicate that the occipital condyle may be a viable anatomical structure for occipitocervical fusion. Although posterior occipital condyle screw fixation is considered a feasible occipital-cervical fusion technique, it is not suitable for high vertebral arteries, stenosis pedicles, and previous cervical fusions. 18 Oral anterior occipital condyle screw fixation (AOCS) can be used safely in these situations. In addition, AOCS can be combined with posterior occipital-neck fusion to provide strong support and maintain alignment.

In this study, we aim to use commercial 3D reconstruction software packages to analyze anatomical parameters and evaluate the optimal screw trajectory of AOCS, and design a board based on these parameters. Then, by using human cadaver specimens, we tested the feasibility and accuracy of AOCS.

Forty healthy adults underwent CT scans of the cranial vertebral junction from July 2017 to November 2018 (Philips Medical Systems, Eindhoven, The Netherlands), and they were included in this study. The exclusion criteria are as follows: 1) patients younger than 25 years old or older than 65 years old, 2) history of surgery at the cranial vertebral junction, 3) abnormalities including Klippel-Feil syndrome, atlas assimilation and basal invagination, 4) trauma, tumor , Rheumatoid arthritis. Then, they generated a 3D model of their cranial-vertebral junction based on the CT data, and measured the parameters of the virtue screw inserted into the model.

Then the anterior occipital condyle screw fixation plate was designed to verify the feasibility and accuracy of specimen simulation. The flowchart of this research is shown in Figure 1. All patients provided written informed consent to participate in our study. This study was approved by the Ethics Committee of the Affiliated Hospital of Ningbo University School of Medicine. All patients gave informed consent, and this study was carried out in accordance with the Declaration of Helsinki. Figure 1 This picture shows the flow of this research.

Figure 1 This picture shows the flow of this research.

According to our analysis, there were 40 eligible patients with an average age of 35.4±7.6 years (22 males and 18 females). Then the CT scan results of all patients were converted into DICOM 3.0 format and imported into the commercial 3D reconstruction software Mimics 19.0 (Materialise, Leuven, Belgium). Generate a 3D reconstruction model of the skull base, occipital bone and atlas (Figure 2). Figure 2 (A) Sagittal plane and (B) the front view of the 3D reconstruction model of the skull base, atlas and vertebral artery.

Figure 2 (A) Sagittal plane and (B) the front view of the 3D reconstruction model of the skull base, atlas and vertebral artery.

After generating the 3D models, we inserted the anterior occipital condyle screws in these models. The best approach should have the longest bicortical screw length and not invade the sublingual canal or vertebral artery. The needle insertion point is located at the medial caudal end of the anterior occipital condyle, and a screw is inserted at the needle insertion point with the direction of the screw pointing to the deformed part of the occipital condyle and skull base (Figure 3). Then we import the 3D model and screws into 3-matic (Materialise, Leuven, Belgium), and use the Analyze Tool to construct the horizontal plane (P1) and vertical plane (P2) of the foramen magnum and the long axis of the screw. The angles between the screw and P1 and P2 are the inclination angle and the divergence angle (Figure 4). Figure 3 The sagittal (A) and axial (B) views of the anterior occipital condyle screw fixation, and the sublingual canal undamaged by the screw. Figure 4 (A) 3-matic 19.0 skull base, occipital condyle, AOCS, vertebral artery and atlas 3D model, (B) the divergence angle measurement of AOCS and the vertical plane of the foramen magnum (P2), (C) AOCS and occipital major The inclination of the hole level (P1) was measured without damage to the sublingual canal or vertebral artery.

Figure 3 The sagittal (A) and axial (B) views of the anterior occipital condyle screw fixation, and the sublingual canal undamaged by the screw.

Figure 4 (A) 3-matic 19.0 skull base, occipital condyle, AOCS, vertebral artery and atlas 3D model, (B) the divergence angle measurement of AOCS and the vertical plane of the foramen magnum (P2), (C) AOCS and occipital major The inclination of the hole level (P1) was measured without damage to the sublingual canal or vertebral artery.

The plate is designed according to the parameters of the junction between the anterior occipital condyle screw and the cranial vertebrae (Figure 5). Ten human body specimens were collected from our hospital. Age and cause of death are unknown. The specimen was confirmed as normal cranial vertebral junction by CT scan, and any deformity, trauma, tuberculosis, tumor and rheumatoid arthritis were excluded. Figure 5 Front view (A), top view (B) and side view (C) of the 3D reconstruction model of the board.

Figure 5 Front view (A), top view (B) and side view (C) of the 3D reconstruction model of the board.

First, we generated 3D models of 10 specimens in Mimics 19.0 based on CT scans, and placed the plate models on the anterior part of the occiput and atlas. Secondly, insert the screws according to the steel plate model. Finally, we imported the 3D model into 3-matic 19.0 and measured the AOCS parameters.

After exposing the anterior occipital condyle and atlas, first place the plate at the junction of the cranial vertebrae, and the plate assists in the placement of screws. Second, we performed CT scans of these specimens to determine if there was any injury to the sublingual canal or vertebral artery. Finally, the parameters of the AOCS in the sample and the 3D model were measured and compared (Figure 6). Figure 6 (A) This image shows the anterior occipital condyle screw and plate fixation in a cadaver specimen. Axial (B) and sagittal (C) views of the CT scan of the anterior occipital condyle screw fixation in the cadaver specimen, and the sublingual canal is not damaged by the screw.

Figure 6 (A) This image shows the anterior occipital condyle screw and plate fixation in a cadaver specimen. Axial (B) and sagittal (C) views of the CT scan of the anterior occipital condyle screw fixation in the cadaver specimen, and the sublingual canal is not damaged by the screw.

All results are expressed as mean ± standard deviation. In SPSS version 21.0 (Chicago, IL), the inclination angle, divergence angle and screw length of the left and right occipital condyles of the volunteer 3D model were analyzed by comparative t-test. The occipital condyle inclination angle, divergence angle and screw length were compared between the specimen model and the specimen by t test. P<0.05 was set as statistically significant in this study.

All 3D models were successfully inserted with screws, and there was no injury to the sublingual canal or vertebral artery. The screw parameters of the anterior occipital condyle are shown in Table 1. There was no significant difference in the left and right parts of the parameters of the anterior occipital condyle screw (P>0.05). The total inclination angle is 5.9°±3.4° (0.6°~11.9°), the divergence angle is 26.7°±6.0° (17.1°~37.7°), and the screw length of all models is 21.6±1.2mm (19.1~25.0mm). Table 1 Parameters of the anterior occipital condyle screw on the volunteer 3D model

Table 1 Parameters of the anterior occipital condyle screw on the volunteer 3D model

Before inserting the anterior occipital condyle screws in these ten cadaver specimens, we performed a CT scan and imported the data into Mimics 19.0 to generate a 3D model. Then we inserted the anterior occipital condyle screw into the 3D model of the specimen and measured the parameters, including the inclination angle, the divergence angle and the screw length. Next, insert the anterior occipital condyle screw with the aid of the steel plate. The model and test piece parameters are shown in Table 2. There is no significant difference in the inclination angle between the specimen model (5.8°±0.5°) and the specimen (5.7°±0.5°) (P=0.42). Similarly, the divergence angle and screw length between the sample model and the sample were not statistically different (26.7°±5.4°, 21.6mm±0.7mm VS 21.7°±1.0°, 20.3mm±6.0mm, P>0.05). Table 2 Comparison of test piece model and test piece screw parameters

Table 2 Comparison of test piece model and test piece screw parameters

In recent years, the incidence of tumors, tuberculosis, and trauma at the cranial vertebral junction has been on the rise. Many scholars have reported the dangers and challenges of these diseases. 19,20 Posterior occipital fusion has been widely used in the reconstruction of the cranial vertebral junction, because of the satisfactory clinical results. The posterior occipital-neck fusion may have some complications, including nonunion and screw loosening, dura mater tear, infection, and inability to relieve nerve pain. 21 In addition, when the inner occipital crest is under the occiput, the posterior occipital squamous screw and plate fixation cannot be performed 22 Although the posterior occipital condyle screw is an alternative technique for skull base abnormalities or previous skull base surgery 23, many important anatomical structures such as vertebrae Arteries, C2 nerve roots and posterior cervical muscles will be damaged during the operation. The posterior approach is exposed, which may cause neck pain. 24,25 For patients with some anatomical variations, such as C2 isthmus stenosis and missing bone structure, posterior pedicle screws may not be feasible. 26,27 As for anterior occipital-neck fusion, total resection is a method of reconstruction of the upper cervical spine, which has reportedly achieved satisfactory results. 14, 28, 29 Similarly, it has also been reported that ramp screw and plate fixation are a feasible technique for anatomical cranial spine reconstruction. 30 However, both surgical methods have some disadvantages. The above method has some complications and risks, including 1) The internal structure of the slope is the midbrain and foramen magnum containing the medulla oblongata, which may be injured when the slope screw is inserted. Invasion of the cranial cavity is a fatal risk. 2) Exposure of the vertebral venous sinus and nerve plexus around the upper cervical spine in the posterior approach may cause bleeding if injured. 31

Therefore, our group intends to design an alternative surgical method to prevent the aforementioned difficulties and complications. Bosco et al. reported the morphometric evaluation and anatomical parameters of the occipital condyle. The results showed that the average length, width, anterior height and posterior height of the occipital condyle were 18.8±2.3 mm, 10.3±1.5 mm, 13.2±2.2 mm and 8.5±1.6 mm, respectively. ,respectively. In addition, the occipital condyle can securely fix the screw without invading the sublingual canal. 32 Similarly, our group reported the same results in a CTA-based study. 33 As for the evaluation of cadaver specimens, Yu et al. reported that a total of 404 mm posterior occipital condyle screws were successfully inserted into twenty (40 occipital condyle) cadaver specimens. Postoperative CT scans confirmed that no screws had invaded the sublingual canal. 34 According to these studies, the occipital condyle may be a viable anterior bone structure reconstruction at the cranial vertebral junction. AOCS has proven to be a feasible and safe technique for stenosis of the C2 isthmus and high vertebral artery. However, important surrounding structures need to be considered. The inner side of the head of the occipital condyle is the sublingual canal, which contains the hypoglossal nerve and the foramen magnum 35. Therefore, in the sagittal plane, if the anterior occipital condyle screw is placed at a large angle, it may invade the hypoglossal canal and damage the hypoglossal nerve. On the contrary, if the screw is inserted too much to the tail or inside, it may invade the vertebral artery or foramen magnum, which may cause damage to the spinal cord and medulla oblongata. 36,37

In this study, we recruited 40 healthy adults with CT data of the cranial vertebral junction and generated a 3D model using Mimics 19.0 software. The digital anatomy and cadaver study at the cranial vertebral junction confirmed the anatomical feasibility of the anterior occipital condyle screw and plate fixation, and initially verified the entry point and optimal trajectory of the AOCS. According to our results, the best trajectory for AOCS insertion is that the sagittal plane tilt angle is 5.9°±3.4°, the axial divergence angle is 26.7°±6.0°, and the average screw length is 21.6±1.2 mm. Researchers report that screws longer than 18 mm can have sufficient pull-out strength. 38 As for the simulation of cadaver specimens, all AOCS were successfully inserted with the aid of steel plates, and there was no hypolingual canal injury or cortical rupture. Then perform a CT scan and use Mimics 19.0 software to generate a 3D model. After that, the parameters of the anterior occipital condyle screw were measured and compared between the specimen model and the specimen. There was no statistically significant difference in the inclination angle, divergence angle, and screw length between the two groups (P>0.05). This shows that the anterior occipital condyle screws can be safely placed with the aid of steel plates. The use of steel plates can improve accuracy and reduce the risk of damage to important surrounding anatomical structures.

Pay attention to the sublingual canal when screwing the anterior occipital condyle, because the hypoglossal canal containing the hypoglossal nerve and venous plexus leads from the skull to the upper anteromedial occipital condyle, and its position determines the safe area for screw placement. Usually, the sublingual tube is located on the anterior medial side of the occiput, but in some patients, the sublingual tube is located on the posterior medial side of the occipital condyle. Therefore, when the sublingual tube is located on the posterior medial side of the occipital condyle, we should analyze the CT scan of each patient and determine the inclination angle. 39 In addition, monitoring the function of the hypoglossal nerve during the operation is helpful for the anatomical positioning of the sublingual triangle and reflects whether hypoglossal nerve damage has occurred during the operation. 40,41 Therefore, correct preoperative diagnosis and imaging results analysis should be performed before anterior occipital condyle screw fixation.

The main indications for AOCS fixation are as follows: 1) anterior cranial junction reconstruction combined with posterior occipital-cervical fusion; 2) upper cervical spine abnormalities, such as C2 isthmus stenosis; 3) occipital condyle fracture; 4) upper cervical spine posterior fixation failure Patients who cannot undergo a second operation. However, patients with occipital condyle or vertebral artery malformations should be considered contraindications. The significance of AOCS fixation is as follows: 1) a new insertion point at the base of the skull; 2) rescue techniques when other occipitocervical fusions fail or are unavailable.

This study has some limitations. First, the simple scale of volunteers is not ideal, but this is a study aimed at proposing new technologies and testing their feasibility. Secondly, due to the limited source of specimens, only ten cadaver specimens were simulated for anterior occipital screw fixation. Although all specimens are safely inserted into the anterior occipital condyle screw, this technique still needs a lot of research to further confirm. Finally, anterior occipital condyle screw plate fixation is feasible, but whether it can achieve immediate stability and sufficient support strength requires biomechanical research and further clinical research.

In summary, AOCS fixation for the reconstruction of the cranial vertebral junction is a feasible and safe surgical technique, and it can be regarded as a rescue technique in the end. More importantly, the placement of anterior occipital condyle screws with the aid of steel plates can improve accuracy and avoid risks.

AOCS, anterior occipital condyle screw; CVJ, cranial junction; 3D, three-dimensional.

All data can be obtained from the corresponding author upon reasonable request.

All patients signed a written informed consent form to participate in our research. This study was approved by the Ethics Committee of the Affiliated Hospital of Ningbo University School of Medicine. All patients gave informed consent, and this study was carried out in accordance with the Declaration of Helsinki. In this study, there are no identifiable individuals or clinical details and any identifying images that have been published.

Informed consent was obtained from all individual participants included in the study.

The contributions of each author to this article are as follows: Dingli Xu (data collection, manuscript writing); Peng Yujie (methodology); Yang Wang and Haojie Li (software measurement, statistical analysis); and Ma Weihu (preparing diagrams and revising manuscripts). All authors have made significant contributions to the work of the report, whether in terms of concept, research design, execution, data acquisition, analysis, and interpretation, or in all these areas; participating in drafting, revising, or critically reviewing articles; final approval requirements Published version; agreed on the journal to which the article was submitted; and agreed to be responsible for all aspects of the work.

The role of the National Natural Science Foundation (81572217) is to design data interpretation and write manuscripts. The Natural Science Foundation of Zhejiang Province (LY18H060002) participated in the design of this research.

The author declares that there is no conflict of interest related to this research.

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