Gender-Associated Differences in Sacral Morphology Do Not Affect Feasibility Rates of Transsacral Screw Insertion. Radioanatomic Investigation Based on Pelvic Cross-sectional Imaging of 200 Individuals.

Abstract

Retrospective radioanatomic single-center cohort study. To investigate sex-specific differences in transsacral corridor dimensions, determine feasibility rates of transsacral screw placement without extended safety zones around planned screw positions, and develop an index defining sacral dysmorphism (SD) irrespective of transsacral corridor diameters. Previously reported SD definitions used radiologically identifiable pelvic characteristics or predefined minimum diameter thresholds of transsacral corridors in the upper sacral segment including safety zones for screw placement. Technical progress of surgical 3D image guidance improved sacral screw insertion accuracy questioning established minimum diameter threshold-based SD definitions. Datasets from cross-sectional pelvic imaging of 100 women and 100 men presenting to a general hospital from July 2018 through August 2018 were included in a database to evaluate transsacral trajectory rates, and dimensions of transsacral corridor lengths, widths (TSCWs), and heights (TSCHs) in sacral segments I to III (S1-3). SD was assumed, if no transsacral trajectory was found in S1 with a corridor diameter of at least 7.5 mm. Women presented significantly higher rates of transsacral trajectories in the inferior sector of S1 (P = 0.03), and larger transsacral corridor lengths in S2 (superior sector, P = 0.045), and S3 (central position, P = 0.02). In men, significantly higher feasibility rates were found for the placement of two transsacral screws in S2 (P = 0.0002), and singular screws in S3 (P = 0.006), with larger S1- (P = 0.0002), and central S2-TSCWs (P = 0.006). SD was prevalent in 17% of women, and 16% of men (P = 0.85). Calculating TSCW ratios of S1 and S2 was significantly indicative for SD at values below a threshold of 0.8 in women (P < 0.00001), and men (P = 0.0004). SD is independent of sex despite significant differences in sacral morphology. An index defining SD irrespective of absolute transsacral corridor dimensions is presented to reliably differentiate dysmorphic from nondysmorphic sacra in women and men. 2.