The Sexual Dimorphism and Age-Related Changes of the Lesser Pelvis in Human. Summary of the Doctoral Thesis

Abstract

The doctoral thesis “The sexual dimorphism and age-related changes of the lesser pelvis in human” is devoted to three main issues: sexual dimorphism concerning pelvic parameters’ averages, their variances, and correlations among the parameters; prediction of the narrowest pelvic diameters; and aging tendencies in the pelvic architecture. Lesser pelvis parameters were detected for a sample of live human participants that constitute an essential difference from previous studies, which detected pelvic parameters on skeletal collections. As a modern method, the three-dimensional computed tomography (CT) provided a possibility for reconstructing of bony pelvis with individual width of pelvic joints and measuring lesser pelvic parameters in human. In order to assess sexual dimorphism of the lesser pelvis, pelvic diameters were detected in four slope axial planes at levels of the inlet, the acetabulum centers, the ischial spines, and the outlet. In addition, four pelvic angles were detected: pelvic inclination, sacral slope, subpubic angle, and sacral anatomical orientation angle. Taking into account that general anthropometric parameters were not detected, an index of proportion was calculated for each of the four planes in order to evaluate pelvic shape as independent of height. Three transverse diameters of the greater pelvis and a transverse diameter of the thorax (between 10th ribs) were analyzed in order to evaluate differences in correlations among diameters of the lesser and the greater pelvis and specific aspects of body sexual dimorphism. Sexual dimorphism was investigated as differences between means and differences in variance of parameters. It was hypothesized that the parameter with lower variance in females than in males is placed in the pelvic cavity at the level of ischial spines. Interrelations of pelvic parameters was analyzed within a regression model evaluating dependence of the narrowest lesser pelvis diameters on other lesser and greater pelvic diameters. These relations were previously studied only as a correlative relationship. Scientific papers represent a limited overview of age-related changes in bony pelvis. Previous studies demonstrated aging tendencies in the position of the sacrum, but do not describe changes of pelvic cavity parameters at different levels in the sagittal and coronal planes. Taking into account sexual dimorphism of the lesser pelvis, it was hypothesized that patterns of age-related changes of pelvic parameters differ in females and males. The research sample included 392 participants (181 males and 211 females) aged from 18 to 84, who were undergoing abdominal or pelvic organs’ CT examination from the October of 2009 to the November of 2010 at the Department of Radiology, Hospital “Gaiļezers” (Riga Eastern Clinical University Hospital). The pelvimetry was performed retrospectively on three-dimensional pelvic CT images. The main results of the thesis show different intensity of the sexual dimorphism at different levels of the lesser pelvis. The highest level of sexual dimorphism and lower variance in index of proportions in females than in males were detected at the level of ischial spines that confirms the hypothesis. Lower variance at the level of ischial spines was not previously described. This new finding confirms higher intensity of adaptation to evolutionary changes concerning this cavity level. The results also demonstrate sexual dimorphism in pelvic architecture. Parameters of the lesser pelvis are closer interrelated in females than in males. For both sexes, clinically significant pelvic dimensions (the sagittal diameter and the transverse diameter at the level of ischial spines) are more closely related to other parameters of the lesser pelvis, but are not sufficiently closely related to parameters of the greater pelvis and to the diagonal conjugate. This means that these dimensions are poor predictors for the narrowest pelvic diameters. Contrary to the hypothesis concerning sexual dimorphism in aging tendencies, the results indicate similar age-related changes in both sexes. The only exception is an index of proportions at the level of ischial spines. This parameter decreases with age in males, but does not change in females. This finding adds to understanding of pelvic sexual dimorphism. The overall changes impact sagittal and frontal dimensions of the bony pelvis. For both sexes, the distance between acetabulum centers remains constant. Unchangeable position of the pelvic rotation center in the frontal plane can provide efficient locomotion throughout human lifespan.