• epidural space;
  • sacrum;
  • anesthesia;
  • caudal;
  • anatomy


The knowledge of sacral hiatus anatomy is imperative in clinical situations requiring caudal epidural block for various diagnostic and therapeutic procedures of the lumbosacral spine to avoid failure and dural injury. In this study, a detailed anatomic study of the sacral region was carried out on 49 male adult Indian cadavers. Dorsal surface of sacral region was dissected to study sacral cornua, sacral hiatus, and the dimensions of triangle formed by the right and left posterosuperior iliac spines with apex of the hiatus. Midsagittal sections were subjected for various anatomical measurements. The angle of needle insertion and the depth of caudal space were noted. Cornu was not palpable bilaterally in 7 (14.3%) and palpable unilaterally in 12 (24.5%) specimens. Mean (standard deviation) distance between apex of hiatus and coccyx tip was 57.5 (8.7) mm and length of sacrococcygeal ligament was 34.2 (7.4) mm. The dimensions of the triangle were found to be interchangeable in 25 cadavers. Once the needle is introduced into the canal after penetrating the sacrococcygeal ligament, it should not be advanced >5 mm to prevent dural puncture. The level of maximum curvature of sacrum was S3 in 34 (69.4%) of cases. The dural sac was found to terminate at S2 in 41 (83.6%). The mean (SD) angle of depression of the needle was 65.7 (5.5) (range 58–78). The measurements described for the identification of the sacral hiatus, optimal angle of depression, and depth of the needle may improve the safety and reliability of a caudal epidural block. Clin. Anat. 22:730–737, 2009. © 2009 Wiley-Liss, Inc.