Cortical Bone Thickness and Morphological Variation in the Greater Sciatic Notch of the Human Pelvis

Abstract

This study analyzes the relationship between cortical bone thickness and shape in the greater sciatic notch (GSN). This bony feature is sexually dimorphic in humans, with males typically exhibiting narrow GSNs and shorter posterior aspects, or cords. In contrast, females typically exhibit wide notches with expanded posterior aspects and more even anterior and posterior cords. The expanded posterior aspect in females appears to contribute to spacious birth canals and is often attributed to obstetric selection. Nevertheless, the proximate mechanisms that produce pelvic sexual dimorphism are unclear.Here I assess GSN variation in 48 females and 50 males aged 0–20 years using decedent computed tomography (CT) data from the Center for Forensic Imaging at the University of New Mexico. I measured cortical bone thickness at the GSN edge and at the pelvic and gluteal aspects adjacent to the notch in Amira software on CT slice planes axial to the posterior and anterior cords. Paired t‐tests assessed cortical thickness differences between the anterior and posterior cords in the three regions. Relative cortical thicknesses were calculated in each of the three regions as the ratio of cortical thickness of the posterior GSN cord to that of the anterior cord. Two‐block partial least‐squares (2B‐PLS) analysis assessed the relationship between relative cortical thicknesses and GSN shape as measured by Procrustes‐aligned 3D landmark coordinates.I also tested for the effects of age on GSN shape and relative cortical bone thickness. For example, results from the 12–14 year and 15–20 year age cohorts indicate that the difference in cortical bone thickness between the posterior and anterior GSN cords at the gluteal aspect is significant (p<0.01), with the posterior cord typically showing greater cortical thickness in this region. Results from the 2B‐PLS analyses suggest moderate but not significant covariation between GSN shape and relative cortical thickness. Among 12–14 year‐olds, deeper GSNs trend with a greater amount of cortical bone in the posterior cord relative to the anterior cord. Among 15–20 year‐olds, greater relative cortical bone in the posterior cord at the GSN edge and gluteal aspect tends to be associated with a lack of a piriform tubercle and a posteriorly displaced notch apex, such that the posterior GSN cord appears shorter. Less relative cortical thickness in the posterior cord tends to be associated with a prominent piriform tubercle and anterior expansion of the superior portion of the anterior cord, such that the notch appears relatively wider. Variables do not clearly associate by sex.Greater cortical thickness in the posterior GSN cord's gluteal aspect relative to that in the anterior cord suggests that the former can better withstand compressive strains related to bipedal posture. Despite insignificant covariation, moderate relationships between relative cortical bone thickness and GSN shape, particularly in terms of notch expansion patterns, suggests that biomechanical mechanisms contribute to GSN morphological variation.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.