Sacral hiatus (arrow) with the sacral cornu (∗). (Reproduced with permission from Dr. Danilo Jankovic)
Chronic low back pain with radicular pain secondary to disc herniation or radiculitis not responding to conservative treatment can be considered for caudal canal injection. It is especially useful when there is difficult anatomy in the lumbar spine, such as previous lumbar surgery or degenerative changes, limiting transforaminal or interlaminar access to the epidural space.
Position: Prone or Kraske position with the buttocks separated.
Probe: Linear probe is generally used. A convex probe rarely is needed, except in some cases of obese patients.
Figure 17.4 Upper panel. A transverse scan is performed first and the structures need to be identified are the sacral cornua (SC), the apex of the sacral hiatus (indicated with bold arrows), and the sacrococcygeal ligament (line arrows). The caudal epidural space (∗∗∗) is the hypoechoic area in between the surface of the sacrum and the sacrococcygeal ligament.
Figure 17.4 Lower panel. The transducer is turned 90 degrees to have long-axis view of the sacral canal. The sacral canal (∗∗∗) and the entrance (bold arrows) covered by the thick sacrococcygeal ligament (line arrows) are well appreciated.
Needles: 17G Tuohy epidural needle (when catheter insertion is planned); or a 3.5-inch 22G spinal needle
Drugs: Volume 10–20 mL with diluted local anesthetic and 40 mg Depo-Medrol (volume depending on using catheter or not)