158 - Sacral Asymmetry: Relationships Between Morphological and Metric Analyses

Poster Board Number: 158
There are separate poster presentation times for odd and even posters.
Odd poster #s – first hour
Even poster #s – second hour

Abstract Body : Variability in the gross morphology of the sacrum can be attributed to directional asymmetries associated with unbalanced mechanical loading forces. These unbalanced mechanical forces produce unequal bone hypertrophy, promoting the formation of observable directional asymmetries of the sacral alae and promontory. Asymmetry of the sacrum may produce abnormal somatic function of the surrounding structures such as the pelvis and lower limbs. Previous studies have used osteological landmarks on the superior aspect of the sacrum to attempt to quantify sacral asymmetry. However, asymmetry between sacral promontory height and bilateral alar height has not previously been defined or correlated with linear sacral measurements, leaving a gap between the current knowledge of sacral asymmetry and potential clinical implications for somatic dysfunction. The objectives of this project were to (1) develop an ordinal scoring system for bilateral sacral alar height asymmetry and (2) investigate potential correlations between 3D morphological asymmetry and 2D linear measurements using a modern, documented skeletal collection. The Southeast Texas Applied Forensic Science (STAFS) Facility is housed at the Sam Houston State University and maintains a willed body donation program that has resulted in a collection of over 400 skeletons. Data were collected on 92 non-pathological sacra (n = 45 males and 47 females; age range 18-87 years) with five fused segments from the STAFS Skeletal Collection. Linear sacral asymmetry was recorded through nine 2D measurements using standard osteological landmarks. A novel scoring method was developed to grade bilateral alar height asymmetry on an ordinal scale of 1-3, with a score of 1 indicating no asymmetry, a score of 2 indicating mild-to-moderate asymmetry, and a score of 3 indicating extreme asymmetry. Reliability of the linear measurements was assessed using technical error of measurement (TEM) and relative technical error of measurement (rTEM). Additionally, reliability for morphological scoring was assessed using percent agreement, comparing data from two trials on a subsample of the sacra selected randomly for this study. Non-parametric Spearman’s rank correlation tests were used to evaluate the potential relationship between linear measurements of the sacrum and morphological scoring for bilateral alar height asymmetry. Analyses proved that 2D measurements and the novel 3D morphological scoring method were reliable, with all rTEM less than 2% for linear measurements and 94% perfect agreement for morphological scoring. However, non-parametric testing revealed no significant correlations between ordinal scoring of bilateral alar height asymmetry and any linear measurement (all p > 0.05). These results demonstrate that commonly used osteological linear measurements fail to fully capture the range of sacral asymmetry, indicating a need for additional development of current scoring methods. Further study of the ordinal asymmetry scoring method developed through this research will help provide a foundational frame of reference for sacral asymmetry, pathologies, musculoskeletal biomechanics, and somatic dysfunction.