Morphological Asymmetry of the Atlas and Its Clinical Implications

Thickness Asymmetry of the Vertebral Artery Groove: A Dried Vertebrae Study

BACKGROUND

The vertebral artery groove (VAG), located on the posterior arch of the first cervical (atlas) vertebra plays a pivotal role in guiding the vertebral artery's (VA) third part (V3). Deviations in VAG morphology and morphometry (dimensions) can influence vascular dynamics and pose clinical implications.

AIM

The current study delves into the morphometric variants and explores the less-explored morphometric variable of the VAG thickness, highlighting possible laterality (asymmetry).

METHODS

A morphometric investigation was conducted on 141 dried atlas (73 male and 68 female) vertebrae from a Greek adult population. The VAG's minimum thickness was investigated by considering the laterality (sides' differences), gender, and age impact on it. Measurements were performed by two independent researchers, ensuring the data reliability.

RESULTS

A significant asymmetry was identified in the VAG thickness between the left (3.9 ± 0.9 mm) and right (4.1 ± 1.1 mm) (p=0.005) sides, with the left side having the mean minimum thickness. Gender had a significant impact on VAG thickness only on the left side, with females presenting a significantly thinner left-sided VAG (3.6 ± 0.9 mm) than males (4.10 ± 0.7 mm) (p=0.001). Age had no significant impact on the VAG thickness.  Conclusion: The present study underscores the significance of asymmetry in the VAG thickness in craniocervical interventions. This less-explored morphometric variable warrants careful consideration by surgeons during preoperative planning to minimize potential complications. The current findings highlight the importance of understanding the VAG thickness asymmetry and its clinical implications, as this osseous variable may be an index of a different diameter of the VA by side. It is recommended that surgeons incorporate this variable into their preoperative assessments to improve the safety and efficacy of craniocervical interventions.

Morphological Characteristics of the Spinous Process of Axis: Clinical Implications for Cervical Spine Manipulation

OBJECTIVE

The purpose of this study was to evaluate the osseous variation of the axis spinous process as it may relate to palpation by clinicians.

METHODS

Morphologies of the bifid spinous process in the intact dry axis of 121 Chinese adult were investigated and classified. The angular deflection of the spinous processes, the bifid spinous processes (the bifid portions of the spinous processes), and the length of the bifid spinous processes were observed and measured.

RESULTS

The bifid spinous process morphologies were classified into 4 types: inverted-V shape (n = 49), inverted-U shape (n = 50), M shape (n = 18), and nonbifid spinous processes (n = 4). The direction of the spinous processes and bifid spinous processes were consistent because they depended on each other's direction of deviation. When the correlation between angular deflection of spinous processes and bifid spinous processes was analyzed, the right deviations of spinous process specimens (29 cases) showed that angular deflections of spinous processes were equal to bifid spinous processes and there was no statistically significant difference seen between them (t = 0.286, P > .05), whereas in the left deviations of spinous process specimens (49 cases), the angular deflection of spinous processes were not equal in length, but bigger than the bifid spinous processes, which was statistically significant (t = -3.079, P = .003 < .05).

CONCLUSION

The anatomical structure of the spinous processes and the bifid spinous processes vary from one another, but they exhibit some regularity. In clinical spinal manipulation practice, the anatomical characteristic of the axis should be taken into account during cervical static palpation, diagnostic imaging, and treatment.

Radiographic analysis of the anterior to posterior open mouth (APOM) cervical spine view: frequency of atlas transverse process overlap of the inferior tip of the mastoid process

OBJECTIVE

The purpose of this study was to measure the frequency with which the atlas transverse process is overlapped by the inferior tip of the mastoid process based upon radiographic analysis of the anterior to posterior open mouth (APOM) cervical spine view.

METHODS

This is a retrospective study. Anterior to posterior open mouth radiographs (N = 120) were obtained from patient files at a chiropractic clinic. Dimensions were bilaterally measured: the vertical distance from the inferior mastoid to the superior margin of the C1 transverse process (C1TP) and the vertical distance from the inferior mastoid to the inferior margin of the C1TP. The percentage of the C1TP occluded by the mastoid process was calculated by determining the occlusal distance. These percentages were grouped into 4 categories: no occlusion, 1% to 50%, 50% to 99%, and 100%.

RESULTS

The occlusal distance for the left and right ranged from -7.1 to 19.0 mm and -7.5 to 19.5 mm, respectively. The mean occlusal distance was identical on the left and right sides (4.6 [SD, 5.1 mm] and 4.7 mm [SD, 5.0 mm], respectively). The percentage of occlusion for the left and right transverse processes ranged from 0% to 80% and 0% to 100%, respectively. The mean percentage was 6.4% (SD, 16.4) on the left and 6.2% (SD, 16.3) on the right.

CONCLUSION

This study shows that the occlusal distance for the left and right ranged from -7.1 to 19.0 mm and -7.5 to 19.5 mm, respectively. A total occlusion of the C1TP occurred in 1 side of 120 participants in this sample.