Analyzing Pelvic Asymmetry by Sex and Ancestry: Insights From an Osteological Collection

Abstract

Introduction: Pelvic asymmetry has been noted in pelvic imaging, and might influence the development of various spinal pathologies, most notably scoliosis. There is a limited understanding of the relationship between pelvic asymmetry and sex and ancestry, and limited use of 3D modeling. The purpose of this study was to identify pelvic asymmetry and morphology differences between sex and ancestry utilizing 3D modeling on young adults in an osteological collection.

Methods: Thirty-three osteological pelvic specimens aged 18-25 years (average age 21.4 ± 2.0 years) were scanned to create virtual 3D models for analysis. Pelvic asymmetry and morphology were measured and compared across sex (male and female) and ancestry (European American and African American). Multivariate regression analysis was performed to examine the relationship between the variables measured.

Results: Multivariate regression analysis demonstrated statistically significant relationships between innominate-pelvic ring ratio and both sex (p < 0.001) and ancestry (p= 0.003) with larger ratios in male and African American specimens respectively. There was also a statistically significant relationship of greater sacral 1 coronal tilt in European American specimens (p= 0.042). There were no statistically significant differences with sex or ancestry in terms of innominate or sacral asymmetry.

Conclusion: Although there are differences in overall pelvic shape between sex and ancestry, there is no relationship between these two variables versus pelvic asymmetry in the axial or sagittal planes in young adult osteological specimens.

Keywords: ethnicity; osteology; pelvic asymmetry; sex; three-dimensional.

Figure 1. Three-dimensional assembly from a European American 18-year-old female of three individual pelvic bone models created with the ROMER scanning arm

(A) Anterior-posterior view of the pelvic ring. (B) Three-dimensional assembly manipulated to show the cranial-caudal view of the pelvic ring.

Figure 2. Midplane of pelvis dividing right and left sides (midway between acetabula and through pubic symphysis)

The plane is used to create a mirror of the left innominate (white) onto the right innominate.

Figure 3. Percent S1 axial translation versus pelvic ring diameter

This was determined by dividing S1 translation distance (mm) by pelvic ring diameter. The dark line represents the edge of the pelvic midplane. The white line is the edge of a parallel plane which goes through the center of S1.

Figure 4. S1 anterior-posterior (sagittal) translation versus pelvic ring diameter

Using the Y coordinates of the centers of the sacrum and the pelvic ring, the distance between the two centers is calculated and compared in a ratio to the pelvic ring diameter.

Figure 5. S1 coronal tilt

Using the S1 fit plane (superior) and sciatic notch plane (inferior), the angle measured between these planes in the coronal plane represents coronal tilt.

Figure 6. S1 sagittal tilt

Using the S1 fit plane (superior) and sciatic notch plane (inferior), the angle measured between these planes in the sagittal plane represents sagittal tilt.

Figure 7. Ratio of innominate height versus pelvic ring diameter and S1 to iliac crest height versus pelvic ring diameter

(A) S1 to iliac crest percent height versus pelvic ring diameter. A plane created by selecting three points on the top of the iliac crests is used to measure the distance to the center of S1 by measuring parallel to the plane. The plane and corresponding measurement were created three times for each pelvis and averaged to minimize the variance in the iliac crest. (B) Sagittal view of measurement.

Figure 8. The plane used for comparing S1 tilt in coronal and sagittal planes

The plane crosses through sciatic notches and pubic crest.

Figure 9. Innominate height

The taller of the two sides was used.