The prevalence of concomitant anatomical variations of atlas vertebrae in a south african skeletal collection

Anatomical variations of atlas vertebrae (C1) are common, yet the prevalence of coexistence of multiple variants remains underreported. This study investigated the prevalence, patterns, and demographic associations of atlas variations in a South African skeletal repository. A quantitative osteological analysis was conducted on 706 atlas vertebrae from the Pretoria Bone Collection. Atlases were macroscopically assessed for eleven predefined variations, including anterior and posterior arch defects, arcuate foramen, lateral ponticle, posterolateral foramen, retrotransverse foramen, unclosed and accessory transverse foramina, and bipartite superior articular facets. Demographic data comprised age at death, sex, and subgroup-affinity. Associations were analysed using chi-square tests and Cramer’s V, with reliability assessed using Cohen’s Kappa coefficient. Overall, 52.1% of vertebrae exhibited at least one variation, yielding 505 variants. The most frequent were arcuate foramen (14.3%) and retrotransverse foramen (11.5%). Concomitant variations occurred in 12.6% of atlases, most commonly the arcuate foramen–retrotransverse foramen combination (2.8%). Significant demographic associations included arcuate foramen in males ( p = 0.035), unclosed transverse foramen in individuals of South African Black subgroup affinity ( p = 0.022), and bipartite superior articular facet in the South African White subgroup ( p = 0.002). These findings demonstrate considerable atlas morphological diversity and highlight the clinical relevance of recognising both isolated and coexisting variations at the craniovertebral junction.