Nakahashi M, et al. - In view of the often failure of caudal epidural blocks due to the difficulty of appropriate needle insertion, researchers sought to appraise the anatomy of the sacral hiatus using ultrasound imaging. In this retrospective study, 76 patients with spinal disorders were examined for the palpability of the sacral hiatus in correlation to gender, BMI, and the morphology of the sacral hiatus on ultrasound imaging. Observations revealed that the palpability of the sacral hiatus is correlated with the mean distance from the skin to the sacral cornua and BMI, and there is a correlation of sacral base protrusion with the difficulty of needle insertion into the sacral hiatus.