Anatomical Study and Clinical Significance of Atlanto-occipital and Atlantoaxial Assimilation Anomaly in Asian Population.

Background: Atlanto-occipital and atlantoaxial assimilation are rare congenital abnormalities characterized by abnormal fusion of the atlas vertebra with the occipital bone or the axis vertebra, respectively, within the craniovertebral junction. These anomalies can significantly alter the biomechanics and structural integrity of the cervical spine, leading to diverse clinical presentations ranging from restricted neck mobility to neurological deficits. Accordingly, this study aims to investigate the prevalence, anatomical abnormalities, and clinical significance of atlanto-occipital and atlantoaxial assimilation in the Asian population.

Materials and methods: A total of 82 human dry skulls and 82 sets of dry cervical vertebrae were examined for the presence of atlanto-occipital and atlantoaxial assimilation. Detailed morphometric analysis was performed to document the fusion patterns and variations in anatomical structures. The data were analyzed to determine the prevalence of these congenital anomalies and their implications for craniovertebral stability and neurological function.

Results: Among the 82 skulls and 82 cervical vertebrae examined, atlanto-occipital assimilation was identified in 3 skulls (3.65%), whereas atlantoaxial assimilation was observed in 2 cases (2.43%). Combined occurrences of both anomalies were found in 2 skulls (2.43%) of the sample.

Conclusion: A thorough understanding of atlanto-occipital and atlantoaxial assimilation is clinically crucial due to its potential impact on the structural and functional dynamics of the craniovertebral junction. These congenital anomalies, though infrequent, can pose considerable clinical challenges, including compromised craniovertebral stability and an increased risk of neurological symptoms. Early diagnosis and careful clinical evaluation are crucial for managing potential complications associated with these conditions.