55 - Greater Sciatic Notch Width Variation in Humans

Poster Board Number: 55
There are separate poster presentation times for odd and even posters.
Odd poster #s – first hour
Even poster #s – second hour

Abstract Body : The greater sciatic notch (GSN), a curved feature in the posterior pelvis, is commonly used for sex estimation. Narrow, J-shaped notches are associated with individuals assigned male at birth; whereas wide, U-shaped notches are attributed to obstetric requirements and associated with individuals assigned female at birth. The processes contributing to GSN variation are not well understood, however. Considering that the GSN spans the sacroiliac and hip joints, a positive relationship between GSN width and sacro-acetabular distance is probable. Sacro-acetabular distance is the distance between the center of the first sacral cranial endplate and the bi-acetabular midpoint. The sacro-acetabular distance represents the anterior ray of the pelvic incidence angle. The posterior ray is perpendicular to the center of the first sacral cranial endplate. Pelvic incidence is important for sagittal balance of the upper body over the hip joints. Short sacro-acetabular distances are found in pelves with high degrees of pelvic incidence. These pelves exhibit sacra located more posteriorly displaced form the hip joints. Long sacro-acetabular distances are found in pelves with low degrees of pelvic incidence. These latter pelves exhibit sacra located more directly superior to the hip joints. The current study aims to clarify processes related to sagittal balance that may contribute to GSN width variation by testing for positive relationships between GSN width and sacro-acetabular distance and between sacro-acetabular distance and thoracic height and for negative relationships between sacro-acetabular distance and pelvic incidence and between pelvic incidence and thoracic height.
This study sample consists of re-articulated pelves from the Bass, Terry, and Hamann-Todd collections as well as a sample from medieval Kulubnarti in Nubia representing 76 assigned females and 81 assigned males, aged 19-100 years. I performed ordinary least squares regressions to test the impact of sacro-acetabular distance on GSN width as well as to separately regress sacro-acetabular distance and pelvic incidence on thoracic height. I used major axis regressions to test the correlation between sacro-acetabular distance and pelvic incidence.
Greater sacro-acetabular distance is weakly associated with greater GSN width (R-squared: 0.20699, p= 0.0001), but for a given sacro-acetabular distance, assigned females exhibit greater GSN width. Greater thoracic height is associated with lower pelvic incidence (R-squared: 0.03732, p=0.0151) and greater sacro-acetabular distance (R-squared: 0.26993, p=0.0001) in both sexes. For a given thoracic height, assigned females show greater sacro-acetabular distance. Sacro-acetabular distance and pelvic incidence are negatively correlated (Fr: -0.4901151, p< 0.001; Mr: -0.3910989, p< 0.001). For a given pelvic incidence, assigned females show greater sacro-acetabular distances.
Results support a connection between GSN width and factors relating to sagittal balance. This study highlights the importance of considering proximal processes that contribute to variation rather than simply ultimate causes, such as obstetric selection.