Descriptive observational study, with a sample universe of 1387 CBCT examinations obtained from the database of the Oral and Maxillofacial Radiology Service of the School of Dentistry, Universidad Andrés Bello, Viña del Mar, between January 2014 and December 2020. Regarding the inclusion criteria, CBCT images were used where the atlas could be observed. The exclusion criteria were: CBCT exams whose field of vision did not allow the atlanto-occipital joint to be observed, CBCT exams with significant movement artifact that prevented correct observation of the atlanto-occipital area, and exams with metal devices close to the atlanto-occipital joint that prevented its observation. correct observation. Probabilistic convenience sampling was performed, obtaining 722 CBCT examinations.
The CBCT exams were acquired from the GENDEX brand equipment model GXCB500 (Gendex Dental Systems and Imaging Sciences International LLC, United States), at 120 kV, 5 mA, with an exposure time ranging between 12.6 s and 23 s, and a voxel of 0.125 mm or 0.2mm. To acquire the exams, the protocols described by the manufacturer were used.
Reconstructions of the volumetric data set were created using Icat Vision® software, (Imaging Sciences International LLC, 2004-2008, United States).
Variables:
The following variables were evaluated:
- Presence of PP: the presence or absence of PP was determined in each CBCT, when a hyperdense image was observed over the posterior arch of the atlas.
- Laterality: It was determined in each CBCT on which side PP is present, with possible unilateral presence (right or left) and bilateral presence.
- Degree of ossification of PP: The classification proposed by Cederberg and Stubbs was applied. Geist et al. (2014); Ahn et al. (2018); Tripodi et al. (2019); Gutierrez et al. (2022). Classification that categorizes PP according to its degree of ossification into 4 types:
- Grade 1: absence of calcification around the vertebral artery passage.
- Grade 2: presence of calcifications that extend for less than half the distance between the posterior portion of the superior articular process and the posterolateral portion of the superior margin of the posterior arch of the atlas.
- Grade 3: presence of calcifications that extend more than half the distance between the posterior portion of the superior articular process and the posterolateral portion of the superior margin of the posterior arch of the atlas, but that do not form a complete ring.
- Grade 4: calcification that completely surrounds the passage of the vertebral artery forming a complete bony ring.
- Age distribution: The age of the subject to whom the CBCT belongs at the time of acquisition is determined. They were grouped into three age ranges which ranged from: 0 to 20 years (group 1), 21 to 40 years (group 2), and 41 or more years old (group 3).
- Gender: it is determined whether the CBCT belongs to a female or male subject.
Calibration:
Prior to the observation and analysis of the CBCT images, a calibration process was carried out between the examiners, obtaining a Kappa index of 0.9, which is very good agreement.
Each observer reviewed a maximum of 35 CBCTs per day. In the multiplanar reconstruction, the data were configured with slices with an interval and thickness of 0.2 or 0.25 mm and the presence of PP was observed in sagittal, axial and coronal slices. The degree of PP ossification was observed in sagittal sections.
The data collected in the study was recorded in an Excel® 2016 spreadsheet for Microsoft 365 MSO (version 2110 build 16.0.14527.20234) by the same operator without recording the patient's personal identification.
Data Analysis:
Data analysis was performed using the JASP 0.13.1 statistical program (jasp-stats.org Department of Psychological Methods, University of Amsterdam, Nieuwe Achtergracht 129B, Amsterdam, The Netherlands). The Chi-square test was applied to determine the relationship between the presence of PP and the gender and age variables, while descriptive statistical tools were used to evaluate the frequency, development and bilaterality of PP. For all tests, a significance level <0.05 was accepted.
This study has the approval of the scientific and ethics committee of the School of Dentistry, Andrés Bello University, Viña del Mar headquarters.