Sexual dimorphism of the pelvic girdle from 3D images of a living Spanish sample from Castilla-La Mancha

The aim of our study is to provide data regarding the morphology of the pelvic girdle from a living Spanish sample. The material used comprises radiographic images (CT scans) from 74 adult individuals (39 ♂ and 35 ♀) in DICOM format. The variables recorded were the bi-iliac width and the antero-posterior and transverse diameters of the three anatomical planes of the birth canal, with the exception of the transverse diameter of the outlet. Indices of the inlet and mid-plane were also calculated. Statistical analysis of the data (Student's t-test and principal component analysis) revealed that the variables which display sexual differences are the transverse diameter of the inlet, the antero-posterior and transverse diameters of the mid-plane and the mid-plane index. In particular, Spanish women have significantly higher values in the transverse diameter of the inlet and the antero-posterior and transverse diameter of the mid-plane than men; and Spanish men have significantly higher values in the mid-plane index than women. The results of this study are in accordance with those obtained in previous studies based on dry bone, which suggest considerable populational variability in pelvic and birth canal geometry. This kind of CT-based study of living populations may significantly enhance our understanding of population variation of pelvic morphology. This information can be useful to better understand the birth mechanism in Homo sapiens and the appearance of rotative birth in the Homo lineage through comparison with the other primates, living or fossil.