Four modalities in the evaluation of the pelvic canal in South Africans

Abstract

Variations in the size and shape of the pelvic canal need to be taken into consideration when planning childbirth, as well as for procedures involving the pelvic canal, pelvic floor and perineum. Although variations between sex and ancestral groups, as well as correlations with stature and aging have been described, studies considering the extent of these differences when childbirth or surgical procedures are planned are limited. The aim of this study was to document the shape and size of pivotal dimensions by means of four modalities of the pelvic canal in South African individuals of African (SAA) and European (SAE) ancestry. A total of 121 intact cadaver pelves, distributed between the sexes and ancestral groups, were sampled from both the University of Pretoria and Sefako Makgatho Health Sciences University. Twenty-eight pelvic landmarks were marked, digitised and direct measurements were measured including the subpubic angle. Shape analyses were performed on the digitised points. Pivotal measurements were repeated on 77 magnetic resonance images (MRI) and 92 computed tomography (CT) scans. Basic descriptive statistics, tests for statistical significance and correlations with age and stature were made. All horizontal measurements of the pelvic canal and the subpubic angles were significantly greater in SAE females than in the other groups and correlated with the greatest dimensions found in the literature. Measurements of SAA females corresponded with other African groups and were larger than in SAA males. Females of both ancestral groups presented, as expected, with a significantly more spacious pelvic canal shape. Longitudinal dimensions were the greatest in SAE males, apart from the true height of the pelvis which was greater in SAA males. Females and SAE presented with statistically wider pelvic canal shapes anteriorly, creating greater anterior pelvic spaces and subpubic regions. The shorter pubic symphysis in SAA females encroached on this space longitudinally. Pelvic outlet shape variations were not statistically significant. Pelvic dimensions (more evident in SAE and females) had a stronger positive correlation with stature than with aging. When comparing modalities, especially when considering MRI, measurements crossing the midline were less repeatable. Taller SAE women may present with larger dimensions, facilitating childbirth. Stature should, therefore, be considered when selecting childbirth options. The smaller inlet and anterior pelvic space in SAA women might cause obstructed labour, however the foetal size should be considered. A narrower pelvis was found in SAA and in males, which may impede vision, access and space for surgical excisions and lead to technical difficulties. The perineal space was also smaller as a result of smaller subpubic angles and intertuberous diameters in males and more specifically, SAA males, which might influence the ease of performing of procedures. Antenatal or pre-operative pelvimetry on MRI or CT scans for comparison with population specific reference values could be useful when considering childbirth options or pelvic and perineal procedures. Care should be taken when interpreting the diameters crossing the midline on MRI scans. Future studies involving more individuals and verified in the clinical setting could be useful for improving the relevance of this study.