Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P15. Pelvic incidence is associated with sacral curvature, sacroiliac joint angulation and sacral ALA width

Abstract

BACKGROUND CONTEXT Pelvic incidence (PI) is a position independent parameter that quantifies the sagittal balance of the pelvis and spine and is associated with several pathologies. We have noted on gross inspection that there appears to be a strong correlation between sagittal sacral shape and pelvic incidence. Previous literature has not addressed the impact of sacral morphology on PI and it is unclear how anatomical characteristics of the sacrum, such as the curvature and sacroiliac (SI) joint angulation, may be associated with PI. PURPOSE This study evaluates how the SI joint angulation, midsagittal sacral curvature, and sacral ala width, relate to pelvic incidence. STUDY DESIGN/SETTING Anatomical comparative study. METHODS A total of 120 cadaveric sacra were obtained from an osteological collection. Pelvic incidence was measured in a previously validated method. To gauge ala width, calipers were used to measure the distance between the midpoint of the sacral endplate and the anterolateral aspect of the right and left ala. Sacral curvature was evaluated by measuring the difference of the direct distance and the curved bony distance from the sacral promontory to the inferior aspect of the fourth intervertebral foramen. Three separate angle measurements were made to quantify the angulation of the SI joint, which we divided into an upper and lower limb. Angle 1 approximated the relationship between the upper limb and the sacral endplate; angle 2 between the upper and lower limb; angle 3 between the lower limb and a tangential line to the fourth sacral foramen. RESULTS Average age at death for all specimens was 31.9±6.3years with 63% representation of males and an equal distribution of Caucasians and African Americans. The mean PI of our study population was 45.1±12.6°. Results from our regression showed statistically significant associations between our measured angles evaluating SI joint angulation (angles 1, 2, and 3) and PI. Standardized beta for angle 1 was −0.421, angle 2 was 0.419, and angle 3 was −0.439 (all p CONCLUSIONS Our data support the theory that increased PI is associated with a highly angulated and curved sacrum, with corresponding changes in the SI joint, and widened sacral alae. Future research into these relationships may help clarify the origins of abnormal pelvic incidence and assist in addressing its pathophysiology.