A morphometric study on enhancing first-pass success in ultrasoundguided caudal epidural access: dorsal sacral foramina as strategic navigational landmarks

Objectives: Anatomical variability often compromises caudal epidural access using traditional landmarks. This study quantifies thespatial relationship between the dorsal sacral foramina (DSF) and the sacral hiatus (SH) to establish a precise navigational frameworkfor ultrasound-guided (USG) access.Materials and Methods: Thirteen formalin-fixed adult cadaveric sacrococcygeal regions were dissected to expose the posterior superioriliac spines (PSIS), DSF, and SH. Horizontal distances from the median sacral crest (midcrest line, MCL) to the PSIS and DSF levelswere measured. The sacral hiatus apex (SHA) position relative to the DSF was analyzed via digital imaging.Results: The mean inter-PSIS distance was 9.1 cm. Lateral distances of DSF3 and DSF4 from the MCL were consistently 0.4 times thePSIS-to-MCL distance. The SHA was localized at or between DSF3 and DSF4 levels in 84.6% of cases. The vertical distance betweenDSF3 and DSF4 was 2.1 cm, matching a standard fingerbreadth. A traditional equilateral PSIS-SHA triangle was observed in only46.1% of cases.Conclusion: The lateral distance of DSF3 and DSF4 from the MCL consistently represents a 0.4 ratio relative to the inter-PSIS distance.Incorporating this ratio and the ‘fingerbreadth’ vertical interval may provide a useful navigational framework for USG caudal access,particularly in anatomically challenging scenarios.