Morphological analysis of occipital condyle and superior articular facet of first cervical vertebra and its congruence in a Thai population

The atlantooccipital joint, which involves the articulation between the occipital condyles (OC) at the base of the skull and the superior articular facet of the first cervical vertebra (C1), is considered a moderately reliable joint for congruence analysis. Evaluating the congruence of OC and C1 in terms of shape and measurement is critical for re-associating disarticulated cranial and postcranial elements in cases of commingled human remains. This study examined the morphological characteristics and congruence between OC and C1 in a Thai population. A total of 201 OC and C1 samples, including male and female specimens, were analyzed to classify their shapes and measurements. The most common OC shape was oval, while the C1 superior articular facet was predominantly eight-shaped. Males exhibited significantly larger OC and C1 measurements across all variables compared to females. Discriminant analysis showed an accuracy rate of 58.2%-70.1% for sex classification. Pearson's correlation coefficients for OC and C1 measurements ranged from 0.490 to 0.818, with the highest correlation observed for the maximum breadth of OC and C1. Sex-specific analysis revealed that males had the highest correlation for maximum breadth, while females showed the highest correlation for minimum breadth. The regression equation for predicting the paired size of OC and C1 had an accuracy rate of 39%-54.46%. These findings contribute to understanding craniovertebral morphology and have implications for forensic identification and surgical planning at the craniovertebral junction.