Original ArticleAnatomic Variations of the Anterior Atlantodental Joint and Relations to the Apical and Alar Ligaments in a Geriatric Population
Introduction
The upper cervical spine has been the subject of numerous studies in relation to congenital malformations, inflammatory processes, and trauma.1, 2, 3 Although the true incidence of malformations of the upper cervical spine is unknown, it is estimated that 5% of people are born with cervical spine anomalies.4 Degenerative changes in the upper cervical spine can result from age-related degeneration or a pathologic process of numerous systemic disorders, such as rheumatoid arthritis; in addition, some anatomic studies have focused on the anomaly of the upper cervical spine, especially the atlantodental joint,5, 6, 7 such as an os odontoideum.5, 6 To our knowledge, the relationship between the normally attached ligaments (apical and alar) at the anterior atlantodental joint and such anomalies has not been well researched. Therefore, the aim of our study is to evaluate for anatomic variations of the anterior atlantodental joint observed in cadaveric dissection of the upper cervical spine in a geriatric population and their association with these regional ligaments. Such information could shed light on stability issues of the craniovertebral junction in patients with bony anomalies.
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Materials and Methods
The upper cervical spine including part of the occiput was dissected in 11 fresh adult human cadavers (8 males and 3 females). The average age of the cadavers at death was 78.9 years (range, 72–90 years). To observe the anterior atlantodental joint from a posterior view, the posterior arch of C1, the spinal cord, and cruciate ligaments were removed in all specimens. Care was taken to preserve the ligamentous attachments between the base of the skull and C1 and C2. The anterior atlantodental
Results
Seven cadavers (64%) were found to have an unusual prominence that was seen arising from the apex of the dens, forming a bony excrescence in the coronal plane, and extending superior beyond the anterior arch of C1 toward the anterior rim of the foramen magnum (Table 1). We have coined the term dens corona for these structures (Figure 1). For these 7 specimens with a dens corona, the alar ligaments were attached to the lateral aspect of the apex of the dens, and they did not attach onto the dens
Discussion
Our study examined malformations of the anterior atlantodental joint in adults and found that the tip of the dens was elongated and extended superiorly above the C1 anterior arch as a dens corona in 7 of 11 (64%) specimens. Although the true incidence of congenital anomalies in the upper cervical spine is not known, it is estimated that 5% of individuals have some form of cervical spine malformation.4 In most specimens in the present study, there was associated arthritic involvement of the
Limitations
The main limitation of this study, as with every cadaver study, is the application to actual patient care. Although we used frozen fresh cadavers, the tissue properties differ from those found in living subjects. The mean age at death in this study was 78.9 years, and this could have an influence on our results.
Conclusion
In our cadaveric dissection of the adult anterior atlantodental joint, we identified the presence of bony prominences arising from the dens (dens corona) and from the atlas (dens aureola). Cadaveric examples of os odontoideum were also identified. The possible etiologies and the clinical applications of these anomalies should be understood by the clinician treating patients with disease in this area or interpreting imaging in the region.
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Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.